DEPARTMENT O F ENERGY

WAVE ENERGY S T E E R I N G COMMITTEE

U N I T E D KINGDOM WAVE ENERGY PROGRAMME

CONSULTANTS' 1981 A S S E S S M E N T

P R E L I M I N A R Y I N F O R M A T I O N

MARCH 1982

RENDEL PALMER & T R I T T O N C o n s u l t i n g E n g i n e e r s , 61 S o u t h w a r k S t r e e t , L o n d o n S E 1 1 S A

I n A s s o c i a t i o n w i t h : KENNEDY & DONKIN C o n s u l t i n g E n g i n e e r s , P r e m i e r H o u s e , W o k i n g , S u r r e y G U 2 1 1 S G

INDEX

1. Status of the Document

2. Some Preliminary Conclusions

3. Comparative charts and tables

Key Summary (Fig 1)

Energy Cost Make-Up Sheet (Fig 2)

Undiscounted Capital Cost 2GW Scheme (Fig 3)

Discounted Total Cost of Scheme per Metre of Structure (Fig 4)

Discounted Cost of Energy (p/kWh)(Fig 5)

Discounted Cost of Air Devices by Function per Metre Length (Fig 6)

Discounted Cost of Air Devices by Function for the 2GW Scheme (Fig 7)

Energy Costs of Air Devices by Function (Fig 8)

Device Capture Efficiencies in the 46 S.Uist Spectra (Fig 9)

Comparison of Device Capture Efficiency (Fig 10)

Comparison of Mean Annual Power Captured per Unit Length of Structure (Fig 11)

Comparison of Overall Station Efficiency (Fig 12)

Comparison of Mean Annual Power Landed per Unit Length of 2GW Station (Fig 13)

Relationship between Captured Power and Swept Volume (Fig 14)

Comparison of (Swept Volume) (Structural Volume) by Device (Fig 15)

comparison of (Mean Annual Power) (Cost of Anchoring the Device) (Fig It

Comparison of (Mean Annual Power) (Total Anchor Force Provided) (Fig 17)

Civil Construction Requirements for 2GW Installation (Fig 18)

4. Notes on Specific Topics

(i) Basis of Costing Civil Construction

(ii) Costing of Device Installation

(iii) Costing of M and E Plant and Transmission

(iv) The Framework of Cost Appraisal

(V) Assessment of Availability

(vi) Data Used in Productivity Assessment

(vii) Assessment of Productivity

5. Device Data Sheets & Notes

(i 1 Bristol Cylinder

(ii) Lancaster Flexible Bag

(iii) Oscillating Water Coluinns

a. NEL Bottom Standing Terminator

b. Vickers Terminator

c. Vickers Attenuator

d. Belfast

e. NEL Floating Terminator

f. NEL Floating Attenuator

(iv) Edinburgh Duck

(V 1 Lanches ter Clam

6. Where the Money has Gone

(A pull out illustration giving allocation of costs)

7. What is the Available Resource at South Uist?

1. S T A T U S O F DOCUMENT

AND

2 . SOME P R E L I M I N A R Y C O N C L U S I O N S

Data Base

STATUS OF THE DOCUMENT

At 30th November the information from Device Teams was

incomplete in many areas, and changing almost from

day to day. This was in part because lessons learned

from tank testing, or costing of designs were being

applied to produce revised designs very late in the

programme. In other cases late or incomplete testing

and designing simply had not produced the data needed.

Numbers produced for E.T.S.U. at that date were totally

unreliable and declared to be so by R.P.T.

In the case of some Teams, interaction with R.P.T. early

in December and the results of the first costing exercise

stimulated significant and urgent redesign to improve cost

effectiveness, so that up to the present date 3.2.82,

new data is still being presented to the Consultants,

and in the absence of calculations, this has had to be

validated by experience and extrapolation.

However, advantage has been taken by R.P.T. of the areas

of similarity between devices to fill in missing numbers,

and to correct obvious anomolies, so that the overall

picture is more reliable than would otherwise be the case.

During the period since November 1981 the opportunity has

also been taken to cross fertilise between devices and

to credit all devices of a type with any particularly

cost effective solution that can be of general benefit.

An important result of late design development has been that

for some devices (NEL, Bristol) the design offered for

assessment is different in some measure from the design

tested in the tank. Alternatively, for other devices,

time and resources have not allowed adequate testing.

In these instances the production of reliable productivity

data has been impossible, and important questions remain

to be answered in further testing.

Productivity is crucially dependent on the power flux in

the sea, and this is perhaps equally uncertain in deep

and shallow water. The main problem is the uncertainty

surrounding the directionality of the energy in the sea.

A short paper is included on this topic.(See Section 7).

There has not yet been enough data, or enough time for

analysis to produce the cost distributions which are the

ultimate requirement from the assessment. Fig. 3 uses

a star rating to identify broadly the security of data.

Compared to previous assessments, there is greater

certainty concerning the predicted costs of the civil

structure. Other very important areas, such as

availability were dealt with globally in previous years and

are now the subject of proper analysis, albeit from a weak

data base.

In summary, across all devices, the following broadly

applies. In rough order of certainty we would list

Civil Engineering Structure (well defined)

Transmission Costs (based on recent tenders)

*~oorings and gravity Anchors (unit pricing well defined)

M&E plant (incompletely specified undesigned, novel)

Installation of Bottom Mounted Devices (many uncertainties)

Productivity (many assumptions)

Availability

Maintenance

(no very helpful (experience for data (base

Interpretation from the data base

Overall the Consultants have the sense that they are

seeking to place firm numbers on to devices which are

in some cases still evolving by step changes. Combined

with the weakness of the data base itself, the result can

not be other than unsatisfactory, and there is the

strongest feeling that more time is needed to study and

analyse the data so recently presented.

This said, a number of trends can be discerned, and some

conclusions can be drawn which are unlikely to be

overturned by the six month's work which most teams still

have ahead of them.

2. SOME PRELIMINARY CONCLUSIONS

1. TWO devices are clearly internally uneconomic, or less

good than other similar devices and can be dismissed from

further consideration. These are :-

Belfast

N.E.L. floating attenuator

2. The Lanchester Clam has a combination of identifiable

good features which satisfactorily explain its present

position as the most economic air device, but closer

examination is needed to determine just how good it is - and if it could be made even better.

3. The relatively close grouping of the air devices in overall

economic terms conceals a key difference between them.

See Fig. 6 and Fig. 10. The fixed NEL Terminator

combines high cost of structure and installation with

high efficiency because of its fixed reference frame.

Conversely the compliant spine of the Clam confers low

structure cost and lower efficiency. The submerged

Vickers devices see less power and have to survive lower

forces.

A very careful comparative study and analysis of these

designs is required to determine where,in the spectrum of

compliance and productivity,lies the optimum pneumatic

device. This must precede any decisions to go forward

with or to reject specific pneumatic devices.

4. The very high forces attracted by fixed devices, and

the potential cost of locating them on a rocky bottom in

shallow water is a key factor in pushing up their cost.

Typically a breakwater is resisting 1 0 0 to 300 times the

force resisted by the compliant mooring of a floating

device of the same length.

5 . Pneumatic devices are predicted to have high availability

on the basis of current technology, (in contrast to

hydraulic power take offs).

6. Consideration of Fig. 8 shows the somewhat surprising

fact that it costs as much to get the power out of the

air,to Skye as it does to get the power out of the sea

into the air. Much more work has been done on the

latter, and instinctively one might expect that the

greatest scope for cost savings probably lies with the

M&E side .......

7 . ..... Transmission is seen to be an almost crippling on-cost to all schemes, There is a factor of almost five dividing

the conceptualcosting of Merz McLellan for a future

scheme and the hard contract price for a current project

in the English Channe1,which K&D have used for the #

Consultants assessment.

The key raw material of the copper is less than 2% of the

final cost of the cable as laid. This is an unusual

ratio, which seems to offer the prospect for a

possible technical breakthrough in the future.

8. The Duck is a device which is conceptually almost perfect

as a power absorber and converter, but requires a level

of reliability in hydraulic components one to two orders

above that allocated by YARD. Should this prove to be

achieveable, then the device could realise its target

availability, and the conceptual cost of power wduld

become a reality and the device would be a winner.

It is important to appreciate that the fine matching of the

power take off to the incident waves is made possible by

the hydraulics and is not available to other devices,

although 'latching' can give useful benefits to

pneumatics.

The Consultants believe that there is not evidence enough

to conclude at this time that the performance specified

by the Duck team will not be available in the future,

and a considered view must be taken of this device for

the medium to long term.

9. The Bristol Cylinder has not yet fulfilled the high

expectations which were engendered two years ago by its

elegant hydrodynamics. The high costs of installation

and power take-off have led to disappointing high cost

of power, even allowing for a degree of tuning and an

optimised cylinder design which have still to be proved

in tank testing.

It is interesting to note that this device is in fact

conceptually the non symmetrical,terminator,version of

the TI device which has been studied for TAG 1.

TI is a point absorber with power extracted from the

heave motion, but no power extracted from the surge.

The cylinder extracts from the surge also, thereby

doubling the theoretical efficiency . TI has been

costed out cheaper than the cylinder. A careful

comparison needs to be made to establish if there are

lessons to be learned that can improve the cylinder

significantly.

Answers to this question can probably be obtained

within the remainina period of the McAlpine Contract,

The potential benefits of tube pumps have already been

admitted to the current costing exercise.

3 . COMPARATIVE CHARTS & TABLES

n m m

D I S C O U N T E D C O S T O F ENERGY ( P I k W h )

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- A N C A S T E R /// // X/)CJ j \ \ ; \ \\1 = L E X I B L E

EDINBURGH I U C K

l//" K x f l \l

3 A G

Y E L F L O A T I N G 4 T T E N U A T O R

/'////KN,\X%i<X):I\'\\' X\'\\\] \, '.

/ ,S'

N E L BTM. STDG. T E R M I NATOR

// ,,' / L i

NEL F L O A T I N G T E R M I N A T O R

V I C K E R S TERM1 N A T O R

A>. \

V I C K E R S ATTEN UATOR

~////'///i"xx>ch\\\l

K E Y TO F U N C T I O N S '

N E L B T M S T N D G TERM.

V 1 C K E R S A T T E N .

V l C K E R S T E R M .

P R O V I D E R E A C T 1 O N S U R F A C E

R E S I S T W A V E I N D U C E D F O R C E S

C O N T A I N A I R 1 W A T E R

C O N V E R T P O W E R

T R A N S M I T

S E L F A S T

L A N C H E S T E R C L A M

L A N C A S T E R F L E X I B L E B A G

N E L F L O A T I N G T E R M .

( P l kSn/h) C O S T OF A B S O R B I N G E N E R G Y I N T O A I R 1 C O S T OF E X T R A C T I N G E N E R G Y F R O M A I R ( P l k W h ) A ' I

* 8 6 4 2 0 2 4 6 8 10

Device Capture Factors in the L6 South Uist Spectra

LFB Clam.

J ~ - - - - - - - - - - - - - + L 6 8 10 12 1L

Te ( sec) Te (sec)

C Bristol Cyl inder.

Tile r c s r i l t s f r ~ l m 1-hc Clam and n r i s t o l (:y L i n d e r have hi?i.n f u r t h e r m o d i f i e d t o t n k e a c c o u n t o f chnngcs i n d e v i c e c r , n i i j i u r a t i o n i n ordc.r t o . l r r i v e a t t h e meal1 a n n u a l p r o d u c t i v i t y ( s e c s ~ c t i o i i s L ( v i ) , 4 ( v i i 1, 5 ( i ) and S(..,)).

4. Tiic ii~cari povcr c l c n s i t y r ~ s r d I ~ a s becn t h n t s p c c i f i c d i n t h e

f u l l s p c c t n ~ m s n i t . ih ly r r o n s f o r m e d t o t h e c o r r c c t d e p t h ( : : i ,ct ion h ( v i i ) ) , i n c l u t l i n g t h o s r i .omyonrnts nnL m o d c l l e d h y t h e wave t ;~r tk .

Figure 9 .

5 . I h r c l 1 a r a c t c r i . ; t i c d ~ m e n s i n n h , ~ s b e e n t a k e n as i l e v l c c l c n g c h f o r a l l e r r e p t t l i r V i c k c r s A t t e n c l a t o r w11c.r~ t h e , . . . 3 L . , . .

1 . . ffl 0

I I I I I

NEL FC TNG ATTEN

VICKERS 1 ATTEN

L F B

4

VIC KERS TERM

.h

LANCHESTER CLAM

N E L FLOATING TERM

N E L BTM STNDG TERM

EDINBURGH DUCK

BRlSTOL CYLl NDER

BELFAST DEVICE -

'M STNDG TERM i

l 1

I

U R G H D U C K

N.E.L. F l t g P Atten.

b L.F. B.

L a n c h e s t e r C l a m .

N.E.L. F l t g . Term,

B e l f a s t D e v i c e

V i c k e r s Term.

Bristol Cyl i nder

Vic kers Atten.

E d i n b u r g h Duck

N.E.L. Btm. stndg. Term.

I - C:,

COMPARISON OF S W E P T V O L U M E BY D E V I C E ( A T RATED POWER)

STRUCTURAL VOLUME

0 BELFAST N E L N E L B T M N E L

F i T N b S I N U G F L T N G -

A T T E N T E R M TERM

L F B V I C I E R S C L A M V I C K E R S D U C K B R I S T O L AT TEN TE HM

Comparison o f Mean Annual

Power per Ern Spent Anchoring

and I n s t a l l i n g t h e D e v i c e

F ig . 1 6

U (lJ W

5 ~ 3 . 0 - -c= ' U 0

"'& ' -4 -W 0 U

L - O 2.5- W ? - > a, a,' -J 07

m L L aJ 0

B-'= O 3 . 0 - n

4

C - m m - #

Cornoarison o f Mean A n n u a l P o w e r p e r Tonne o f A n c h o r a q e F o r c e P r o v i d e d

I J W I I

4.NOTES ON SPECIFIC TOPICS

4 . (i) BASIS OF COSTING OF CIVIL CONSTRUCTION

In view of the difficulties which had arisen in previous years, when

Device Teams costed independently and the Consultants attempted to rationalise

the results - with the inevitable conflicts which arose - for the present round of reporting it was decided that the Consultants would circulate a

\+?orking Paper setting out the approach for the Teams to adopt.

The Working Paper was prepared by a small committee which included

representatives of many of the Device Teams. This ensured that any special

points which the Teams wished to explore were adequately covered and helped

the results to gain general acceptance.

The Working Paper set out standard rates for the most important items

which could be anticipated in a Bill of Quantities and explained in great

detail how these rates were derived.

The detail included rates for labour, plant and materials with build-ups

of on-costs for such things as bonus, sick pay, site offices, overheads etc.

It gave productivity rates so that a Team could check the amount of labour

and plant assumed for a given operation. This Paper also set out (where

appropriate) the limits of applicability of rates. Thus, having the derivation

of the rates, Device Teams were in a position to develop their own rates should

it be felt that the standard rates were inapplicable. The intention was that

this would be the exception rather than the rule.

With this approach, problems of costing were limited to those associated

with the justification for the adoption of a special rate, and the assumptions

made in its derivation.

In order that everything was on a common basis, all rates etc. were

based on those applicable at Hunterston. For this purpose the area at

Hunterston was assumed to be infinitely large and with adequate water depth

at a convenient distance offshore. With this assumption a standard construction

facility, capable of an output of 200,000 cu m of concrete per annum, was

costed. The variable covered in the Working Paper related to the manner in

which the device was launched. Teams had the choice of ship lift, slipway or

flooded basin.

Although all construction facilities were to be norinally at Hunterston,

the intention was that the concept would represent a series of such facilities

at various suitable sites in Scotland. In the event, Teams developed single

larger facilities which indicated economies when compared with the use of

multiple standard facilities. While it is accepted that such an approach could

lead to some economy it could also lead to greater labour difficulties and

4/(i) 11

possible environmental problems. For these reasons, and in order to retain

uniformity of pricing throughout, the most likely costs quoted have in all

cases been based on the use of standard sized facilities but a suitably

weighted design tolerance has been postulated to allow for the possibility

of economies arising from use of large facilities.

THE COSTING OF DEVICE IXSTALLATION

Device installation is one of the most difficult aspects of Wave

Energy to cost. It involves the following:-

1. The development of a feasible overall method of installation.

2. The selection of appropriate marine craft.

3 . The assessment of the time necessary to carry out each marine

operation making up the overall installation method.

4. The assessment of the sea state in which each marine operation

can be undertaken.

5. The statistical likelihood of, and waiting period for the

occurrence of various sea states at the different water depths

in which the Teams propose to site their devices.

Although periodsof good weather can occur at any time of the

year, taken statistically over the lengthy period required for

installation of the devices necessary for a 2GW station, these

factors obviously vary with the season of the year.

6. The further limitations (where appropriate) due to daylight,

fog or current.

7. The costing of the marine craft involved.

In order to assist, the Consultants produced a Working Paper giving

the statistical parameters relevant to 5 and 6 above, and EASAMS gave

iriformation on the cost of a number of marine craft - i.e. those required for

maintenance. Costings for the remainder of the craft were obtained from other

sources.

The costing exercise had to deal with two essentially different types

of device: floating and bottom standing.

The former involve the prelaying of moorings and the hook-up of devices

thereto. Piles set in the rock sea bed were a preferred form of anchorage

and necessitated the use of large specialised craft costing upwards of

£40,000,000 apiece. Specialised clump anchors may prove to be a more economical

solution.

The installation of bottom standing devices involves the local preparation

of the sea bed, the careful lowering of the device and its final anchorage to

the sea bed - in most cases using rock ties. Once again large specialised craft

are involved; in this case faced with the added hazard of working in relatively

shallow water depths.

4/(ii)/l

The approach t o cos t ing lends i t s e l f t o t a b u l a r p re sen ta t ion s e t t i n g out

opera t ions , wave and l i g h t l i m i t a t i o n s , ope ra t iona l du ra t ions e t c . This l eads

t o an eva lua t ion of t h e t o t a l t ime f o r t h e complete i n s t a l l a t i o n procedure, t h e

number of devices which a p re sc r ibed f l e e t of v e s s e l s can i n s t a l i n a year and

hence the number of such f l e e t s (and t h e i r c o s t ) necessary t o enable a l l t h e

devices t o be i n s t a l l e d wi th in t h e time p re sc r ibed by the Device Teams.

COSTING OF M AND E PLANT AND TQANSMISSION -- Where tu rb ines and genera tors have been cos ted by the Teams, these

c o s t s have been checked and i f necessary ad jus t ed t o al low f o r i tems which

may have been omit ted.

I n t he case of t u rb ines and genera tors f o r devices which have no t had

a f u l l design and c o s t i n g e x e r c i s e c a r r i e d ou t by a manufacturer, cos t ing

formulae, based on t h r e e sources of information, have been developed by the

Consul tants t o p r i c e . Addi t iona l ly these formulae ensure t h a t t he p l a n t c o s t s

f o r d i f f e r e n t devices do c o r r e l a t e . I t must be emphasised t h a t t h i s cos t ing

method i s very approximate and of a pre l iminary na tu re and i s a p p l i a b l e f o r

u n i t s up t o lOMW only.

A i r Turbine

Three sources of information were considered t o provide a system t h a t

permit ted a c o r r e l a t i o n of a i r t u rb ine c o s t s .

It must be noted t h a t gene ra l ly because of the v a s t l y d i f f e r e n t

geometries and degrees of complexity i t i s thought a t t h i s s t a g e impossible

t o c o s t a i r t u rb ines genera l ly (Wells, Franc is and Axial flow) according t o

r a t i n g o r speed. The only parameter a v a i l a b l e becomes weight.

Three sources of information were considered t o permit very crude

cos t ings of t u rb ines on a common b a s i s .

1 ) Quote from Airex Ltd. f o r SEA C l a m t u rb ine . This quote was

f o r f45K f o r a s i n g l e s t a g e 3.5m 8 b lade Wells t u rb ine . f5K

was added by SEA t o al low f o r s p l a s h guard, s h a f t ba lanc ing

and module assembly. Estimated (SEA) u n i t weight i s 6.5T.

2 ) Quote from Sirocco f o r B e l f a s t Wells tu rb ine . This i s a

1.25111 2 plane opposed flow t u r b i n e (4 r o t o r s each of 6

b l ades ) . Weight 7.7T. The Sirocco quote was E80K f o r one of

a batch of 5 - quoted r educ t ion for mass product ion i s 20%

i . e . E64K per u n i t .

3) K & D have a tender p r i c e (1978) f o r a 2.3m 0 Franc i s t u rb ine .

This a t 1981 p r i c e s i s equ iva l en t t o a t o t a l of f600K. This

t u rb ine c o s t may be s p l i t i n t o two components:-

a ) t u r b i n e runner - 7T @ 18K/T - f125k

b) a l l o t h e r m a t e r i a l s - 77T @ ~ K / T - f475k

(The turbine runner is a 2.3m @ single multi-blade casting, fully

hand ground to profiles for hydro applications).

A rice reduction of 15% for bulk production brings the total cost to E500K.

The best approximation that can be made at the present time for

turbine costs is assumed to be:-

Wells and rotating parts of other turbines E 8000 /T

Casings, castings, machined housings f 60001T

Diffusers, cnnvolutes, ducting etc. E20001T

Where no weights or drawings are available axial flow turbines have

been priced on other device turbines and factored by the square of the

diameter ratio.

Generator

The costing formula for generators has been developed from three

sources of information:-

1) Clam figure from GEC for 'off the shelf' 1MW generator. This

figure was f43K - 45K for 1MW diesel driven machine. 45K is

the marinised version and has basically a higher insulation

rating and is Lloyds approved for marine use. This price is

for a constant speed machine in a 1.3 MW frame including

cooling fan, casing and mounting. This machine, rated at 1MW

is heat rated to 1.3 MW and is 50160 Hz, 1100 rpm, ex works T

tested and assembled (wt = 8 ).

2) Merz & Mclellan figure for the Duck - 1.2 MW + 3.3 kV switch

gear - 46K per unit.

3) K & D pricing figure for large 'one off' hydro generators. 1

This figure - £3.3 (MW/rpm)'m. is for essentially a constant

speed (but with up to 90% overspeed capability) machine and

includes excitation and both generator and turbine control,

casing, mounting, basic cooling and is F.O.B.

The formula is based on rating and speed. It includes a basic cost l

of £1.56 (MWIrpm) ' million, which figure includes casing immediate to the machine, testing and works assembly. An addition is made of 15% for

variable speed machines and rather over 5% for constant speed machines.

This is to cover excitation control, additional assembly on site, transport

and loading out. Finally an allowance of £6,000 per MW is made for cooling

sepa ra t ion .

The formula i s , therefore : -

I 6 f 1.56 (l4w/rpm) h 10 x 1.15 + (6,000 X MW)

Transmission

The t ransmiss ion scheme inc ludes two subsea c ros s ings , (from the

devices t o the Outer Hebrides and from the Hebrides ac ros s the Minch t o

Skye) p lus t ransmiss ion l i n e s and onshore i n s t a l l a t i o n s on the I s l ands

themselves.

For t ransmiss ion l i n e s , c i v i l works and p l a n t i n s t a l l a t i o n on the

I s l ands (o r platforms o f f sho re ) allowance has been made f o r cos t of

cons t ruc t ion inc rease due t o remoteness, d i f f i c u l t ground condi t ions , poor

access , h igher wages and more expensive t r a n s p o r t arrangements. This has

lead t o an inc rease of between 50 and 100%.

For major submarine cab le l ay ing o f f Outer Hebrides and ac ros s t he

Minch t o Skye, t he Consul tants have been guided by two r e c e n t and major

cab le c o n t r a c t s placed j o i n t l y wi th STK, Oslo, and P i r e l l i , Milan, by BC

Hydro f o r supp l i e s t o Vancouver I s l and . Appropriate supply and l a y r a t e s

have been derived from these a c t u a l and c u r r e n t con t r ac t s .

A coun te rpa r t check was made us ing c o s t of forthcoming channel DC

l i n k (CEGB). Derived c o s t suppor ts r a t e s used i n e s t ima te s . Of i n t e r e s t i s

the f a c t t h a t Consul tants1 r a t e f o r the cab le s t o Skye i s agreed by the Vickers

Team and appears gene ra l ly acceptab le t o LFB Team's Consul tants .

The r a t e s used f o r t he submarine cab le s a r e a s follows:-

400 kV Cables (Hebrides t o Skye) £1.75 m/km 3 phase

275 kV Cables from the devices t o t h e I s l a n d s -

E1.6m/km 3ph (1600mm2) + f l. 4m/km

D.C. S e r i e s Power Connections - 35kV fO.l5m/loop km (800mm2)

THE FRAMEWORK OF COST APPRAISAL

O u t l i n e o f Approach

The c o s t a p p r a i s a l o f t h e u n i t c o s t of energy ( i n pence/kWh) and o f t h e

2GW power s t a t i o n ( i n E M) were under taken i n a n e q u i v a l e n t manner t o

p r e v i o u s y e a r s ; b u t f o r t h i s r e p o r t a computer program h a s been used t o

a l l o w more d e t a i l e d a n a l y s e s t o be under taken r a p i d l y and e a s i l y .

Any a s p e c t o f t h e scheme c o s t s c a n be s p e c i f i e d s e p a r a t e l y , by g i v i n g a

c o s t r a t e , a q u a n t i t y , and r e f e r i n g t o a p r o f i l e o f e x p e n d i t u r e through

t ime. These s e p a r a t e i t ems cou ld b e , f o r example, t h e c o s t p e r d e v i c e f o r

i n s t a l l i n g machinery, t h e c o s t p e r v e s s e l f o r purchas ing a t u g , o r a lump

sum f o r p r o v i d i n g temporary moorings.

The program accummulates t h e p r o d u c t s o f c o s t r a t e , q u a n t i t y and

e x p e n d i t u r e p a t t e r n by y e a r i n t o a framework by y e a r , g i v e n codes f o r each

i t e m a l l o c a t i n g i t t o a c o s t c e n t r e , and a l l o c a t i n g i t t o e i t h e r scheme

c a p i t a l c o s t s o r power s t a t i o n maintenance.

The d e t a i l e d c o s t c e n t r e s , some 16, a r e i n f a c t used a t t h e l e s s d e t a i l e d

l e v e l shown i n F i g u r e s 2 and 3 .

The energy o u t p u t o f each scheme i s c a l c u l a t e d by a p p l y i n g t h e average

a n n u a l energy c a p t u r e d p e r d e v i c e , f a c t o r e d by t h e a v e r a g e power c h a i n

c o n v e r s i o n and t r a n s m i s s i o n e f f i c i e n c y and t h e average a v a i l a b i l i t y , t o a

p r o f i l e g i v i n g t h e number o f d e v i c e s on s t a t i o n i n each y e a r .

Uni t Cost o f Energy

To d e r i v e a n o v e r a l l ave rage u n i t c o s t , t h e v a r i o u s s t r e a m s o f c o s t s and

energy landed have t o be b rough t t o a common b a s i s . For t h e s imple scheme

assumed i n p r e v i o u s y e a r s , t h i s was done by a n n u a l i s i n g t h e t o t a l c a p i t a l

c o s t and add ing i t t o t h e (assumed c o n s t a n t ) y e a r l y maintenance c o s t and

a n n u a l ene rgy landed. For t h i s a s sessment round, because o f t h e v a r i a b l e

s t r e a m s o f a l l t h r e e components a r i s i n g from t h e more d e t a i l e d

assumpt ions adop ted , a d i f f e r e n t ( b u t ma themat ica l ly e q u i v a l e n t ) approach

was used.

A l l s t r eams o f c o s t s and energy were conver ted t o n e t p r e s e n t t o t a l s ,

u s i n g t h e s p e c i f i e d o p p o r t u n i t y c o s t o f c a p i t a l ( d i s c o u n t r a t e ) o f 5

p e r c e n t . The t o t a l accumulated c o s t s were t h e n d i v i d e d by t h e t o t a l

accumulated energy t o g i v e t h e pence p e r k i l o w a t t hour f i g u r e s g iven .

Array C a p i t a l Cos t s

These f i g u r e s a r e S imply t h e und i scoun ted t o t a l e x p e n d i t u r e i n c u r r e d a t

t h e t ime t h e f u l l energy i s deployed.

S e n s i t i t i v i t v T e s t s

S i n c e a l l d e v i c e s have b r o a d l y s i m i l a r p r o f i l e s o f e x p e n d i t u r e and energy

p r o d u c t i o n , changing t h e d i s c o u n t r a t e does n o t a l t e r t h e d e v i c e m e r i t

o r d e r .

Work i s c u r r e n t l y underway on t e s t i n g t h e e f f e c t o f a l t e r e d component l i f e

a s sumpt ions , p r i n c i p a l l y t h e examina t ion o f p ro long ing t h e l i f e o f t h e

c o n c r e t e s t r u c t u r e from 25 t o 50 y e a r s . T h i s produces improvements o f

between abou t 1 5 t o 20 p e r c e n t i n t h e u n i t c o s t s , w i t h d e v i c e s w i t h h i g h

c o n c r e t e c o n t e n t o b v i o u s l y producing t h e h i g h e r s a v i n g s . T h i s may narrow

t h e range of t h e o v e r a l l c o s t s o f power, b u t i s u n l i k e l y t o a l t e r t h e

m e r i t o r d e r .

Cos t , q u a n t i t y and energy t o l e r a n c e s have a l l been e s t i m a t e d f o r t h e

o r i g i n a l d a t a , and t h e i r a g g r e g a t e e f f e c t on t h e sp read o f p o s s i b l e

r e s u l t s has been t e s t e d by r e p e a t e d sampl ing from t h e p r o b a b l e range o f

each of t h e v a l u e s inc luded i n t h e d a t a . The r e s u l t s o f t h i s s e n s i t i v i t y

t e s t a r e be ing used t o g u i d e t h e emphasis o f f u r t h e r work, i n an e f f o r t t o

improve t h e p r e c i s i o n of t h e l e s s w e l l s p e c i f i e d d e v i c e s .

THE ASSESSMENT OF AVAILABILITY

The a v a i l a b i l i t y of t he va r ious devices has long been a s e n s i t i v e

s u b j e c t and u n t i l r e c e n t l y i t has not been p o s s i b l e t o cons ider i t i n a

coherent fash ion . The way has r e c e n t l y opened f o r a more l o g i c a l approach

wi th t h e r e c e i p t of information on f a i l u r e r a t e s now a v a i l a b l e from Yard. These

d a t a cover most of t he i tems of p l a n t used aboard the devices .

Based on the assumption t h a t p l a n t i s given adequate r o u t i n e maintenance,

Yard have suppl ied information on the frequency of f a i l u r e per year . I n

t h i s context i t w i l l be apprec ia ted t h a t a s the number of s i m i l a r p l a n t

elements ( say tu rb ines ) i s increased , so p ropor t iona te ly a r e the numbers of

f a i l u r e s per year .

Yard have a l s o prepared l o g i c diagrams s e t t i n g out t h e sequence and number

of p l a n t elements. This , i n conjunct ion wi th the f a i l u r e f requencies enables

an assessnlent t o be made of the percentages of each of t h e i tems of p l a n t which

( s t a t i s t i c a l l y ) have f a i l e d a f t e r o n e y e a r l s o p e r a t i o n . Hence the percentage l o s s

of power a t t he end of t he year can be der ived .

As t h e l o s s of power i s presumed t o vary l i n e a r l y , t h e average (percentage)

l o s s of power over t h e year i s h a l f t h a t occurr ing a t t h e end of the year . This

would be on the assumption t h a t r e p a i r teams v i s i t each device a t l e a s t once

a year . The percentage a v a i l a b i l i t y i s 100% l e s s t h i s average l o s s .

Should the inc idence of f a i l u r e a t t h e end of the yea r be excess ive ,

cons ide ra t ion has t o be given t o r e p a i r a t more f requent i n t e r v a l s .

To the l o s s of power due t o f a i l u r e of p l a n t must be added l o s s due t o t h e

f a i l u r e of t he t ransmiss ion system, leading t o t he o v e r a l l a v a i l a b i l i t y f a c t o r .

The Consul tants have found t h a t f o r most of t h e devices a s a t i s f a c t o r y

a v a i l a b i l i t y can be achieved on the b a s i s of Yard's f a i l u r e r a t e s associ.ated wi th

a reasonable frequency of r e p a i r v i s i t s .

I n t h e case of t h e Lancas te r F l e x i b l e Bag and the S.E.A. C l a m , t he

r e l i a b i l i t y of t h e f l e x i b l e membranes i s c r u c i a l . Yard have given a range of

f i g u r e s f o r f a i l u r e f o r t hese elements and by t ak ing a f i g u r e r a t h e r nea re r t h e

lower end of t he range, a s a t i s f a c t o r y r e l a t i o n s h i p between a v a i l a b i l i t y and

maintenance can be achieved.

I n t h e case of t h e Edinburgh Duck, a d i f f e r e n t approach had t o be adopted

a s t h e use of Yard's f a i l u r e r a t e s i n d i c a t e d t h a t t h e Duck would n o t be operable .

The assessment of f a i l u r e r a t e s i s a very d i f f i c u l t s u b j e c t - d a t a being

sca rce o r non-exis tent and o f t e n widely vary ing o r con t r ad ic to ry . Hence

Yard's f i g u r e s may be open t o adjustment. This i n f a c t was the ' d i f f e r e n t '

approach adopted by the Consul tants . A reasonable l e v e l of a v a i l a b i l i t y

and maintenance was assumed and the corresponding f a i l u r e r a t e s der ived.

This approach l ed t o a requirement t h a t t h e average f a i l u r e r a t e s t o be

achieved t o make the Duck adequately r e l i a b l e must be 1/50 of those s e t

ou t by Yard.

Yard's i n i t i a l assessment of f a i l u r e r a t e s f o r t he B r i s t o l Cylinder l ed

t o an unacceptably low a v a i l a b i l i t y . But Yard's i n i t i a l i n t e r p r e t a t i o n of

t h e Team's p re sen ta t ion was v e r y pes s imis t i c . Study of the r e s u l t s by

the Team showed f a i l u r e r a t e s could be s u b s t a n t i a l l y reduced a t n e g l i g i b l e

a d d i t i o n a l c o s t , such a s by providing redundancy i n s e a l s . Also f a i l u r e

of a rode does no t cause the extreme l o s s i n p roduc t iv i ty assumed by Yard.

Revised f a i l u r e r a t e s i nco rpora t ing these f a c t o r s have no t been received

by the Consul tants from Yard i n time f o r t h i s r e p o r t . Hence an est imated

a v a i l a b i l i t y f a c t o r of 80% has been used i n the p r o d u c t i v i t y assessment.

The a v a i l a b i l i t i e s der ived inc lude allowances f o r r e p a i r a s we l l a s

l o s s of power p r i o r t o r e p a i r . A longer r e p a i r downtime has been assumed

f o r f l o a t i n g devices due to the g r e a t e r d i f f i c u l t i e s of access . The

a v a i l a b i l i t i e s taken i n t o p r o d u c t i v i t y c a l c u l a t i o n s a r e 80% f o r the Duck

and the Cylinder , between 83 and 86% f o r t he f l o a t i n g devices and 87 - 91%

f o r the bottom s tanding devices .

4 ( v i ) NOTE ON DATA USED I N PRODUCTIVITY ASSESSMENT

. ,

1. The B r i s t o l Cy l inder h a s been t e s t e d i n t h e 46 s p e c t r a s e l e c t e d by

10s . The w a t e r dep th a t t h e in tended d e v i c e l o c a t i o n i s 42m, t h e

dep th a t which t h e s p e c t r a were measured, and t h e r e f o r e no f u r t h e r

t r a n s f o r m a t i o n f o r dep th was n e c e s s a r y .

The Team h a s s u p p l i e d d e t a i l e d r e s u l t s showing t h e c a p t u r e

measured i n t h e t ank and t h e c o r r e c t i o n s n e c e s s a r y t o a l l o w f o r

i m p e r f e c t i o n s i n t h e i r t e s t r i g and s p e c t r a l components n o t

reproduced a t Cadnam. F u r t h e r f a c t o r s have been p r e s e n t e d t o

a l l o w f o r t h e improved p r o d u c t i v i t y which t h e Team b e l i e v e w i l l be

ach ieved wi th a c y l i n d e r o f d i a m e t e r l a r g e r t h a n t h a t t e s t e d and

i n c o r p o r a t i n g v a r i a b l e s p r i n g i n g and damping. The Team h a s d a t a

t o s u p p o r t t h i s , b u t from r e g u l a r wave t e s t s o n l y . F u r t h e r t e s t s

by t h e Team i n t h e n e a r f u t u r e w i l l conf i rm o r c o n t r a d i c t t h e s e

c o r r e c t i o n s . For t h e p r e s e n t t h e C o n s u l t a n t s have a l lowed f o r a l l

e x c e p t t h o s e i n r e s p e c t o f wave components n o t r e p r o d u c i b l e i n t h e

t ank - t h e C o n s u l t a n t s n o t c u r r e n t l y n o t b e i n g i n agreement w i t h

t h e Team over t h e v a l i d i t y o f t h e s e f a c t o r s .

Power c h a i n e f f i c i e n c y c u r v e s have been s u p p l i e d by t h e

C o n s u l t a n t s excep t f o r t h e rode pumps, f o r which a s i n g l e v a l u e

f i g u r e o f 0.85, s u p p l i e d by t h e Team, h a s been used. K & D a r e i n

g e n e r a l agreement w i t h t h e Teams's M & E C o n s u l t a n t s o v e r

e f f i c i e n c y v a l u e s , f o r t u r b i n e s , g e n e r a t o r s and t r a n s m i s s i o n .

2. The Clam h a s been t e s t e d i n t h e 46 s p e c t r a s e l e c t e d by IOS

t r ans fo rmed t o a dep th o f 80m. However, due t o t h e l a r g e s c a l e

f o r t e s t i n g chosen by t h e Team (1 :55) , t h e Cadnam tank was n o t a b l e

t o g e n e r a t e 11 o f t h e h i g h e s t ene rgy s p e c t r a a t t h e s p e c i f i e d Hs.

The Team reduced t h e wave ampl i tude f o r t h e s e s p e c t r a and

e s t i m a t e d c a p t u r e assuming l i n e a r i t y , i . e . t h a t c a p t u r e e f f i c i e n c y

i s independent of wave h e i g h t . T h i s p rocedure , which i n c r e a s e s

t h e c a p t u r e from t h a t measured by 20%, i s c la imed by t h e Team t o b e

v a l i d b u t t h e C o n s u l t a n t s a r e s c e p t i c a l . I n t h e s h o r t term t h e

i n c r e a s e h a s been i n c l u d e d i n t h e C o n s u l t a n t s ' p r o d u c t i v i t y

a s s e s s m e n t , b u t more d a t a i s awai ted from t h e Team.

The Team have proposed f u r t h e r c o r r e c t i o n t o power c a p t u r e f i g u r e s

a l l o w i n g f o r l o s s e s , d i f f e r e n c e s i n geometry between t h e model and

t h e p r o t o t y p e , and c a p t u r e i n s e a s t a t e s o f power l e s s t h a n 10

kW/m. These have been i n c o r p o r a t e d i n t h i s r e p o r t , b u t a r e s u b j e c t

t o c o n f i r m a t i o n by mode1 t e s t s . These c o r r e c t i o n s g i v e a n

a d d i t i o n a l i n c r e a s e i n p r o d u c t i v i t y o f 37%, o f which 16% i s due t o

t h e bag l eng th b e i n g i n c o r r e c t l y modelled. Thus t h e t o t a l

i n c r e a s e i s p r o d u c t i v i t y a p p l i e d t o measured d a t a amounts t o 65%.

Cons tan t power c h a i n e f f i c i e n c y v a l u e s o n l y have been s u p p l i e d by

t h e Team and t h e r e f o r e t h e C o n s u l t a n t s have based t h e number o f

d e v i c e s i n a 2GW scheme a l s o on t h e Team's f i g u r e .

The Duck p r o d u c t i v i t y a ssessment h a s been made from t e s t s i n P-M

s e a s i n t h e narrow tank . Capture from t h e 46 s e l e c t e d s p e c t r a h a s

been e s t i m a t e d by t h e Team by assuming l i n e a r i t y o f performance

(wi th r e s p e c t t o t h e i n c i d e n t d i r e c t i o n o f waves and t h e i r

combina t ion) and i n t e r p o l a t i n g between narrow t a n k r e s u l t s . S t e p s

have been t aken towards s u b s t a n t i a t i n g t h e s e r e s u l t s by t e s t i n g a

s t r i n g o f s i x ducks i n t h e wide t a n k , b u t on a f i x e d s p i n e and i n

r e g u l a r , u n i d i r e c t i o n a l waves.

Power c h a i n e f f i c i e n c y d a t a and t h e number o f d e v i c e s have been

s u p p l i e d by t h e Team.

4 . The LFB h a s been t e s t e d i n t h e 46 s p e c t r a s e l e c t e d by IOS, b u t

t ransformed t o a dep th o f 75m. Capture r e s u l t s have been a d j u s t e d

by t h e Team t o a l l o w f o r l o s s e s i n t h e model. I n a d d i t i o n RPT have

i n c r e a s e d t h e p r o d u c t i v i t y r e s u l t s by 8% t o a l l o w f o r c a p t u r e i n

s e a s o f power l e s s t h a n 10 kw/m and t o remove t h e e f f e c t o f a n

unnecessa ry t u r b i n e c u t - i n v a l u e inc luded by t h e Team. The

t u r b i n e s w i l l c a p t u r e power i n low energy s e a s t a t e s , a l b e i t a t a

much lower e f f i c i e n c y t h a n a t i t s d e s i g n r a t i n g .

Power c h a i n e f f i c i e n c y c u r v e s have been s u p p l i e d by t h e Team and

t h e number o f d e v i c e s r e q u i r e d f o r a 2GW scheme agreed .

5. The NEL Breakwater h a s n o t been t e s t e d i n t h e 46 s e l e c t e d s p e c t r a .

R e s u l t s r e c e i v e d from t h e Team have comprised a s i n g l e t h e o r e t i c a l

monochromatic e f f i c i e n c y c u r v e , which is i n s u f f i c i e n t t o e n a b l e

t h e C o n s u l t a n t s t o make a thorough a s s e s s m e n t o f t h e hydrodynamic

pe r fo rmance o f t h e d e v i c e . Based on t h e i n f o r m a t i o n a v a i l a b l e ,

t h e C o n s u l t a n t s had t o make two a s s u m p t i o n s i n o r d e r t o a s s e s s t h e

d e v i c e pe r fo rmance i n t h e 4 6 s e l e c t e d s p e c t r a , i .e. t h a t

(i) t h e d e v i c e p e r f o r m a n c e i s i n d e p e n d e n t o f w a v e h e i g h t .

( i i ) t h e d e v i c e p r o d u c t i v i t y i n a mixed s e a c a n be o b t a i n e d by

a p p l y i n g a c o s i n e r u l e t o t h e 12 u n i d i r e c t i o n a l compone S F o f e a c h m u l t i d i r e c t i o n a l s p e c t r u m and s u b s e q u e n t

s u p e r p o s i t i o n .

The d e v i c e hydrodynamic e f f i c i e n c y t h u s o b t a i n e d h a s b e e n

i n c r e a s e d by 5% t o r e f l e c t t h e i n c r e a s e d d i r e c t i o n a l i t y o f t h e

s e a s , due t o r e f r a c t i o n , a s t h e waves p r o p a g a t e i n s h o r e . T h i s

i n c r e a s e h a s been n e c e s s a r y b e c a u s e t h e 4 6 s e l e c t e d s p e c t r a were

l i n e a r l y t r a n s f o r m e d t o t h e d e s i g n d e p t h o f 21m w i t h t h e

d i r e c t i o n a l d i s t r i b u t i o n o f e n e r g y k e p t c o n s t a n t .

From t h e power c h a i n e f f i c i e n c y c u r v e s p r o v i d e d by t h e Team, t h e

C o n s u l t a n t s ' e s t i m a t e o f t h e number o f d e v i c e s f o r t h e 2GW scheme

a g r e e s w i t h t h e number p roposed by t h e Team.

6 . The NEL F l o a t i n g T e r m i n a t o r h a s been t e s t e d i n t h e 46 s p e c t r a

s e l e c t e d by IOS a t a w a t e r d e p t h o f 42m, f o r which no

t r a n s f o r m a t i o n i s r e q u i r e d . S u b s e q u e n t l y t h e Team have d e c i d e d t o

r e s i t e t h e d e v i c e i n l O O m d e p t h , and i t h a s been assumed t h e

c a p t u r e e f f i c i e n c y r e m a i n s unchanged ( i . e . t h e pe r fo rmance o f t h e

d e v i c e i s l i n e a r ) even though t h e seas a r e more e n e r g e t i c a t t h i s

d e p t h . The Team h a s a p p l i e d no c o r r e c t i o n t o i t s r e s u l t s and

t h e r e f o r e r e g a r d s them a s c o n s e r v a t i v e .

C o n s t a n t power c h a i n e f f i c i e n c y v a l u e s have b e e n s u p p l i e d by t h e

Team, as h a s t h e number o f d e v i c e s r e q u i r e d f o r a 2GW scheme.

7. NEL F l o a t i n g A t t e n u a t o r

No e x p e r i m e n t a l d a t a were s u p p l i e d by t h e Development Team. Hence

t h e p r o d u c t i v i t y o f t h e d e v i c e had t o b e t a k e n a s t h a t quoted by

t h e Team. These r e s u l t s were based on narrow t a n k t e s t s i n

monochromatic s e a s u s i n g pre-1981 p rocedure . Not b e i n g suppor ted

by any e x p e r i m e n t a l r e s u l t s t h e C o n s u l t a n t s have r e s e r v a t i o n s a s

r e g a r d s t h e i r v a l i d i t y .

The C o n s u l t a n t s have a p p l i e d a d i f f e r e n t a v a i l a b i l i t y f a c t o r t o

t h a t quoted by t h e Team, i . e . 0.83 n o t 0.87.

The number o f d e v i c e s r e q u i r e d f o r a 2GW scheme h a s been t aken t o

be t h a t g i v e n by t h e Team - i n s u f f i c i e n t power p l a n t d a t a p reven ted

t h e C o n s u l t a n t s from making an independent e s t i m a t e o f t h e number.

8. The Vickers A t t e n u a t o r h a s been t e s t e d i n t h e 46 s e l e c t e d s p e c t r a

a d j u s t e d f o r r e f r a c t i o n by HRS f o r a dep th o f 25m. Values o f power

c a p t u r e i n t h e s p e c t r a were s u p p l i e d by t h e Team. The Team's d a t a

inc ludes a c o r r e c t i o n f o r d u c t f r i c t i o n l o s s e s , t h e c o r r e c t i o n

producing an i n c r e a s e i n p r o d u c t i v i t y o f around 10% o f t h e

o r i g i n a l v a l u e .

A combined power c h a i n e f f i c i e n c y c u r v e h a s been s u p p l i e d by t h e

Team, who have a l s o determined t h e number o f d e v i c e s r e q u i r e d f o r a

2GW scheme.

9 . The Vickers Termina to r h a s been t e s t e d i n t h e 46 s p e c t r a s e l e c t e d

by IOS t ransformed t o a dep th o f 25m. L i n e a r t r a n s f o r m a t i o n o f

s p e c t r a t o t h i s w a t e r dep th over t h e uneven seabed o f f t h e Hebr ides

i s n o t v a l i d ; t h e s p e c t r a should b e a d j u s t e d f o r r e f r a c t i o n u s i n g

t h e HRS program. The p r o d u c t i v i t y o f t h e d e v i c e i s l i k e l y t o have

been underes t ima ted by n o t t a k i n g accoun t o f r e f r a c t i o n . The Team

have s u p p l i e d v a l u e s f o r power c a p t u r e i n t h e s p e c t r a which they

have c o r r e c t e d f o r d u c t f r i c t i o n l o s s e s , t h e c o r r e c t i o n producing

a n i n c r e a s e i n p r o d u c t i v i t y o f around 30% o f t h e o r i g i n a l v a l u e .

Cons tan t v a l u e power c h a i n e f f i c i e n c i e s have been supp l i e d by t h e

Team, who have a l s o determined t h e number o f d e v i c e s r e q u i r e d f o r a

2GW scheme.

Cons tan t v a l u e power c h a i n e f f i c i e n c i e s have been s u p p l i e d by t h e

Team, who have a l s o determined t h e number o f d e v i c e s r e q u i r e d f o r a

2GW scheme.

10. B e l f a s t Device

P r o d u c t i v i t y a ssessment o f t h e d e v i c e i n i t s c u r r e n t l y proposed

form i s based on narrow t a n k t e s t i n g i n PM s p e c t r a . R e s u l t s have

been a d j u s t e d by t h e Team t o s i m u l a t e c a p t u r e i n t h e 46 South U i s t

s p e c t r a . There i s ev idence t o v e r i f y t h i s approach s i n c e

agreement was found between t e s t s on a n e a r l i e r d e v i c e

c o n f i g u r a t i o n i s b o t h PM s p e c t r a i n t h e narrow tank and t h e 46

s p e c t r a i n t h e wide t a n k a t Edinburgh.

The d e v i c e i s a p o i n t a b f s o r b e r and a s such i t i s impor tan t t o

s t u d y i t s behav iour i n a n a r r a y . However, o n l y a s o l i t a r y d e v i c e

was t e s t e d i n t h e t ank . P r o d u c t i v i t y of t h e p r e s e n t doub le row

a r r a y w i l l t h e r e f o r e be l e s s t h a n model t e s t s p r e d i c t owing t o a s

y e t u n q u a n t i f i a b l e s h i e l d i n g o f t h e second row.

A c o n s t a n t power c h a i n e f f i c i e n c y v a l u e was s u p p l i e d by t h e Team.

4 ( v i i ) ASSESSMENT 01: PKODLIC'TIV LTY

The p r o d u c t i v i t y assessment of t h e v a r i o u s t y p e s of d e v i c e i s based

on a s t e a d y s t a t e model u s i n g e x p e r i m e n t a l random, m u l t i d i r e c t i o n a l s e a

e f f i c i e n c y d a t a i n 46 s e a s t a t e s . These s p e c t r a have been s e l e c t e d by

I . O . S . , t o a l l o w t h e mean annua l p r o d u c t i v i t y of a l l d e v i c e s t o be e s t i m a t e d

i n a f a i r , c o n s i s t e n t and economical manner. T h e i r s e l e c t i o n was made from

a l a r g e r s e t of 399 s p e c t r a , s y n t h e s i s e d from d a t a c o l l e c t e d a t t h e o f f s h o r e

buoy i n 42m of wa te r o f f South U i s t . The 399 s p e c t r a a r e c o n s i d e r e d t o

r e p r e s e n t t h e mean annual s e a c l i m a t e .

P r i o r t o any t e s t s , t h e 46 s e l e c t e d s p e c t r a have t o b e t ransformed

t o t h e wa te r dep th a t which t h e v a r i o u s types of d e v i c e a r e t o be p laced .

Two methods of t r a n s f o r m a t i o n a r e used:

( i ) A l i n e a r i n t e r p o l a t i o n of t h e power l e v e l i g n o r i n g any

r e f r a c t i o n e f f e c t s . T h i s method i s presumed t o b e

s a t i s f a c t o r y f o r w a t e r d e p t h s g r e a t e r t h a n o r e q u a l t o 35m.

The r e c e n t recommendations by TAG 2 t o reduce t h e power i n

t h e s e a a t d e p t h s g r e a t e r t h a n 42m has been implemented by

assuming l i n e a r d e v i c e performance.

( i i ) A r e f r a c t i o n t r a n s f o r m a t i o n f o r wa te r d e p t h s between

35m and 25m.

R e f r a c t i o n e f f e c t s have been t h e s u b j e c t of a n e x t e n s i v e s t u d y by

t h e Hydrau l ics Research S t a t i o n , who under took t h e t a s k of t r ans forming t h e

46 s e l e c t e d s p e c t r a t o 25m of w a t e r . A t even s h a l l o w e r w a t e r dep ths o t h e r

f a c t o r s , such as wave b r e a k i n g , need t o b e invoked t o e x p l a i n t h e observed

power l o s s . The n a t u r e and i n t e r p r e t a t i o n of t h e s e e f f e c t s i s n o t y e t

f u l l y unders tood and they should be t h e s u b j e c t of an e x t e n s i v e r e s e a r c h

programme.

For t h e p r e s e n t , w i t h no f u r t h e r i n f o r m a t i o n , t h e C o n s u l t a n t s used

t h e i r l i n e a r t r a n s f o r m a t i o n method t o produce a n a v a i l a b l e wave c l i m a t e f o r

d e v i c e s a t w a t e r d e p t h s l e s s t h a n 25m. T h i s p l a c e s t h e sha l lower w a t e r

d e v i c e s a t a d i s a d v a n t a g e and a l lowances have t o be made t o t a k e t h i s a s p e c t

i n t o account .

The d e v i c e mean annual p r o d u c t i c i t y i s computed from t h e exper imenta l

random, mixed s e a s e f f i c i e n c y d a t a o b t a i n e d from tank t e s t s i n t h e 46

s e l e c t e d s p e c t r a ( t r ans formed t o t h e a p p r o p r i a t e d e p t h ) . The mean product-

i v i t y of t h e d e v i c e i n t h e s e s p e c t r a i s o b t a i n e d and subsequen t ly modif ied

t o g i v e t h e mean annual p r o d u c t i v i t y . The m o d i f i c a t i o n is n e c e s s a r y i n order

t o t a k e i n t o account t h e f a c t t h a t t h e 46 s p e c t r a (when f a c t o r e d by t h e i r

a p p r o p r i a t e we igh t ings and summed) r e p r e s e n t a d u r a t i o n of 2671399 of a y e a r .

Th i s amounts t o 76.52 of t h e mean annua l energy, t h e remain ing 23.5% a s s o c i a t e d

w i t h t h e 132 s p e c t r a excluded by t h e s e l e c t i o n p r o c e s s account f o r a s follow:;:-

The energy a s soc i a t ed with s p e c t r a whose Te va lue i s o u t s i d e the

range 7-12.9 sec. a r e ignored ( t o t a l energy l o s s 2.5%). Also ignored

a r e s p e c t r a with power l e s s than 10 kw/m. As wel l a s being only a

small percentage l o s s (2 ,4%) , t he power l e v e l i s so low t h a t f i xed

lo s ses w i th in the power cha in w i l l make the generated e l e c t r i c a l ou tput

neg l ig ib l e .

Four s p e c t r a a s soc i a t ed with h igh mean l e v e l s of power 0 3 0 0 kwjm)

were a l s o excluded by the s e l e c t i o n process , I n t h e sea s t a t e s

represented by these s p e c t r a , t h e r e w i l l occur peaks of power f a r g r e a t e r

than can be captured by devices , a cu tof f being imposed on power

captured by the r a t i n g of the p l an t . Hence the h igh mean power l e v e l s

w i l l probably n o t r e s u l t i n increased capture of energy. It i s t he re fo re

assumed t h a t the energy captured i n t hese spec t r a i s the same a s t h e

energy captured i n a s i m i l a r spectrum, bu t of reduced power l e v e l ,

contained i n the s e t of 46. Spectrum 388 has been chosen f o r t h i s

purpose.

F i n a l l y , 27 s p e c t r a were excluded because of unusual combination of

parameters, bu t otherwise ly ing wi th in the bounds of Power and Te of the 46

spec t r a . The energy a s soc i a t ed wi th t h e s e s p e c t r a amounts t o 10.1% of

the annual energy, and the device capture e f f i c i e n c y i n t hese s p e c t r a

i s taken a s the mean cap tu re e f f i c i e n c y f o r t he weighted s e t of 46.

The power cha in p roduc t iv i ty i s obtained by assuming t h a t f o r a given

s e a s t a t e the inpu t power t o the t u r b i n e i s cons tan t . The procedure f o r

ob ta in ing the mean annual p roduc t iv i ty of the power chain, and i t s

i nd iv idua l components, i s s i m i l a r t o t h a t appl ied t o the device.

I n a d d i t i o n t o the s teady s t a t e model, a time domain s imula t ion i s

used, i n c e r t a i n cases , t o quan t i fy a f a c t o r desc r ib ing t h e e f f e c t of t h e

most ques t ionable assumptions made i n t he s teady s t a t e model. This f a c t o r

i s , when appropr i a t e , used t o g ive an improved e s t ima te of device

p roduc t iv i ty .

For reasons of s i m p l i c i t y , t he s imula t ion has been i n i t i a l l y l i m i t e d

t o a s i n g l e degree of freedom, i . e . t h e power cha in r ece ives a s i n g l e random

input . Whils t t h i s i s adequate f o r a device l i k e the NEL breakwater, i t

cannot accu ra t e ly r ep re sen t many o t h e r devices , f o r which s impl i fy ing

assumptions must be made. However, by jud ic ious choice of t hese assumptions,

the time domain s imula t ion can throw u s e f u l l i g h t on those elements of

each device whose performance i s l e a s t wel l descr ibed i n b e s teady s t a t e model.

4 / ( v i i ) I 2

5 . DEVICE DATA SHEETS & NOTES

BRISTOL CYLINDER

LEADING DEVICE PARAMETERS

(Loca t ion - South l l i s t )

BRISTOl. CYI.INI)I:,R -p----

A. Rela t ed t o 10cati.o. 1. ~ i s t a n c e o f f s h o r e (km)

2 . Water dep th (m)

3. Power i n s e a (Kwlm)

3 . Rela t cd t o d e v i c e

1. O v e r a l l s i z e - l e n g t h (m)

- b r e a d t h (m)

- v e r t i c a l d imension (m)

75

15 (d i ame te r )

2 - g r o s s c r o s s s e c t i o n a l a r e a (m )

2 . Weight of d e v i c e ( t o n n e s )

1 7 6 . 7

g000 approx.

120 approx. 3 . Weight of d e v i c e l e n g t h ( tonneslm)

C . Re l a t ed t o 2CW s t a t i o n

1. Number of d c v i c e s

2 . Spacing of d e v i c e s (m)

3 . Length o f 2GW s t a t i o n (km) ( e x c l . nav ig . gaps)

D. G e d t o p r o d u c t i v i t y

1. Ra t ing of g e n e r a t o r s (MW)

2 . Power i n s e a (Kwlm)

120 MwI25 d e v i c e s

4 7 . 8

3. Elean annua l power d e l i v e r e d t o Skye (Elw/device)*

4 . Mean annua l o u t p u t of 2GW scheme (G!.J)*

E . Rc l a t cd t o s t r u c t u r e economy and u t i l i z a t i o n of r e s o u r c e

1 . Mean annua l power delivered p c r d e v i c e I l eng th of dev i ce (Kw/m)*

2 . Mean annua l powcr d e l i v c r c d p e r d e v i c e 6 dev ice s p a c i n g (Kw/m)*

3 . O v e r a l l conve r s ion c f f i c i c n c y of schcme*

mean annua l o u t p u t of 2GW scheme ( 2 ) mean annua l power i n s e n , x l e n g t h o r 2Gli s t a t i o n

4 . Cap tu re Fac to rh*

mean a n n u a l j ' w e r c a p t u r e d by d e v i c e (il) nenn annua l power i n s e a x d e v i c c l e n g t h

F. R e l a t e d t o cost

1. Cost of ?GW s t a t i o n (und i scoun tcd ) ( L W )

2 . Cost of each d c v i c c (und i scoun ted ) (<M)

3. Cost of energy ( d i s c o u n t e d ) (p/Kwh)

G . Misc ,e l laneous

1. Hean annual powcr c h a i n e f f i c i e n c y (7.)"""

2 . A v a i l a b i l i t y of t h e 2G!4 scheme (%)

3.

4 .

* i n c l u d i n g a v a i l a b i l i t y f a c t o r

** n o t i n c l u d i n g a v a i l a b i l i t y f a c t o r

*** mean annua l power landed a t Skyc ( n o t i n c l u d i n g a v a i l a b i l i t y f a c t o r ) mean annua l power cap tu red p e r d e v i c e :.; No. of d e v i c e s i n scheme

General

I n 1981 t h i s d e v i c e was developed i n a articular form i n

c o n s i d e r a b l e d e t a i l s u f f i c i e n t f o r most o f t h e e lements o f t h e

scheme t o have been de te rmined , and w e l l enough d e f i n e d f o r

d e t a i l e d d e s i g n t o be a b l e t o proceed. However a t t h e end of 1981

t h e Team advanced t h e p r o s p e c t i v e improvements i n p r o d u c t i v i t y

which they p r e d i c t e d would be p o s s i b l e i f a s e r i e s of

m o d i f i c a t i o n s were made t o t h e d e s i g n . The e n g i n e e r i n g a s s o c i a t e d

wi th e f f e c t i n g t h e s e changes was n o t developed due t o s h o r t a g e o f

t ime s o t h e c o r r e s p o n d i n g c o s t i n g changes a r e somewhat

s p e c u l a t i v e . However al thorigh t h e r a t i n g s and numbers o f

c y l i n d e r s may be a c c o r d i n g l y a d j u s t e d t o s a t i s f y t h e 2 GW

performance requ i rement , t h e r a t i n g of t h e aggrega ted h y d r a u l i c

power convers ion t o an e l e c t r i c a l o u t p u t and i t s t r a n s m i s s i o n t o

s h o r e i s w e l l e s t a h l i s h e d . The t h r e e h y d r o - e l e c t r i c t u r b i n e

g e n e r a t o r s on each of t h e s i x o f f s h o r e p l a t f o r m s t r u c t u r e s have

f a i r l y p r e c i s e s p e c i f i c a t i o n s . Apar t from b e i n g mounted on a

o f f s h o r e p l a t f o r m , t h e g e n e r a t i n g p l a n t and i t s a s s s o c i a t e d

e l e c t r i c a l equipment a r e o t h e r w i s e e n t i r e l y c o n v e n t i o n a l i n

concep t .

Performance

The comprehensive hydrodynamic t e s t i n g programme s o f a r c a r r i e d

o u t h a s l e d t o a thorough u n d e r s t a n d i n g o f t h e b a s i c p r o p e r t i e s o f

t h e c y l i n d e r i n r e g u l a r waves. It h a s a l s o y i e l d e d v a l u e s f o r

c e r t a i n c y l i n d e r c o n f i g u r a t i o n s of e f f i c i e n c y , and b o t h peak and

r.m.s v a l u e s of rode f o r c e s and c y l i n d e r d i sp lacement i n random

s e a s . However t h e Team i s no t y e t s a t i s f i e d t h a t i t h a s f u l l y

o p t i m i s e d some d e v i c e pa ramete r s o r t h a t i t h a s provided t h e

d e v i c e w i t h t h e b e s t c o n t r o l sys tem f o r optimum r e a l s e a

performance. The r e a s o n f o r t h i s i s p u r e l y t h e t ime l i m i t a t i o n on

t ank t e s t i n g .

The p r o d u c t i v i t y o f t h e d e v i c e on which t h e f i n a l c o s t of mean

annual power and t h e s i z e and c a p i t a l c o s t o f a 2GW scheme d i r e c t l y

depend, d e r i v e s from t h e r e s u l t s of t ank t e s t s i n t h e sub-se t o f 46

s p e c t r a . The method o f i n t e r p r e t a t i o n of t h e r e s u l t s was l a i d down

i n t h e C o n s u l t a n t s ' working paper 42. I n p r i n c i p l e , t h e

p r o d u c t i v i t y c a l c u l a t i o n p recedure i s s t r a i g h t - f o r w a r d b u t t h e

Team h a s i d e n t i f i e d a s e r i e s of c o r r e c t i o n s t o t h e measured d a t a

which have a s u b s t a n t i a l e f f e c t on t h e f i n a l p r o d u c t i v i t y v a l u e .

S e v e r a l of t h e s e c o r r e c t i o n s invo lve changing t h e pa ramete r s of

t h e c y l i n d e r from t h o s e a c t u a l l y t e s t e d , s i n c e t h e team i s

convinced t h a t i t d i d n o t t e s t a model of t h e b e s t p o s s i b l e dev ice .

Also , i m p e r f e c t i o n s i n t h e t e s t i n g r i g e x i s t e d which had a n

a d v e r s e e f f e c t on model performance. F u r t h e r shor tcomings i n

t h e s e t e s t s were t h a t t h e Cadnam tank can produce wave components 0

o n l y from an a r c o f about 150 ( i n s t e a d of 360' a s i n a r e a l s e a )

and t h a t o n l y a s i n g l e c y l i n d e r was t e s t e d a t a t ime i n S. U i s t

s p e c t r a (due t o l i m i t a t i o n s i n t h e a v a i l a b l e i n s t r u m e n t a t i o n ) .

The Team knows from e a r l i e r t e s t s u s i n g an a r r a y o f t h r e e s h o r t e r

c y l i n d e r s , each w i t h o n l y f o u r r o d e s , t h a t c a p t u r e e f f i c i e n c y p e r

d e v i c e r i s e s f o r a l i n e o f d e v i c e s

The r e a l i s a t i o n t h a t c a p t u r e e f f i c i e n c y improvements a r e l i k e l y

w i t h a d i f f e r e n t c y l i n d e r came from t h e Team's s t u d y of p r e v i o u s

t e s t r e s u l t s i n r e g u l a r waves. These i n d i c a t e t h a t i n r e g u l a r

waves, improvements i n c a p t u r e can be made by;

1 ) i n c r e a s i n g t h e c y l i n d e r d i a m e t e r from 12m t o 15m.

2) v a r y i n g t h e s p r i n g and damping f o r c e s a c c o r d i n g t o t h e wave

p e r i o d .

3 ) v a r y i n g t h e r a t i o of s p r i n g s t i f f n e s s e s s and damping f o r c e s

i n t h e f o r e and a f t rodes .

I n a d d i t i o n i t i s known t h a t t h e r e i s a s i g n i f i c a n t d e t e r i o r a t i o n

i n performance i f t h e t h r e e rode s t i f f n e s s e s on one s i d e o f t h e

c y l i n d e r d i f f e r .

T h i s was known t o be t h e c a s e w i t h t h e model t e s t i n g r i g employed,

due t o i m p e r f e c t i o n s . A f u r t h e r s o u r c e o f e f f i c i e n c y l o s s i n t h e

model was i d e n t i f i e d a s t h e f r i c t i o n on t h e p u l l e y s and d r a g on t h e

c h a i n s which cause a phase s h i f t between t h e wave and c y l i n d e r

mot ions , l e a d i n g t o d e c r e a s e i n e f f i c i e n c y . There i s no means o f

q u a n t i f y i n g t h i s l o s s a t p r e s e n t b u t i t was c o n s i d e r e d t o e x p l a i n

t h e s u b s t a n t i a l d i f f e r e n c e s i n model e f f i c i e n c i e s o b t a i n e d i n t h e

same exper iments a t Edinburgh and Cadnam. As a temporary e s t i m a t e

t h e Team h a s a l lowed 9%.

For t h e p r e s e n t p r o d u c t i v i t y a ssessment of t h e form o f d e v i c e

which t h e Team i s advoca t ing i t i s t h e r e f o r e n o t p o s s i b l e i n t h e

p r e s e n t s t a t e of knowledge f o r t h e C o n s u l t a n t s t o work from a mean

annual d e v i c e performance which i s f u l l y s u b s t a n t i a t e d by t a n k

t e s t i n g i n random S. U i s t s p e c t r a . I n s t e a d , t h e Team h a s t a k e n

d a t a from t h e r e s u l t s of t e s t s on a 75m long , 12m d i a m e t e r c y l i n d e r

w i t h f i x e d and e q u a l rode s t i f f n e s s e s ( a l b e i t w i t h e r r o n e o u s

unequal r e s i d u a l v a l u e s g i v i n g reduced performance) and f i x e d

damping. These d a t a a r e t h e n modi f i ed , spect rum by spect rum, on

t h e b a s i s of r e s u l t s i n r e g u l a r 2-D waves, t h e dependant v a r i a b l e T

( t h e wave p e r i o d i n monochromatic waves) b e i n g in te rchanged f o r Te

( t h e energy pe r iod i n mixed r e a l s e a s ) . T h i s m o d i f i c a t i o n p r o c e s s

i n v o l v i n g m u l t i p l y i n g o u t p u t by a c h a i n of t h r e e f a c t o r s assumes

t h a t t h e e f f e c t o f each f a c t o r i s independant of t h e o t h e r s , which

t h e Team c l a i m s t o be s o . The C o n s u l t a n t s have no means o f

conf i rming o r denying t h e p r e d i c t e d p r o d u c t i v i t y . The l o g i c o f r t h e d e r i v a t i o n i s u n d e r s t a n d a b l e , b u t t h e c r u c i a l q u e s t i o n i s how

f a r t h e t e n d e n c i e s i n r e g u l a r waves a r e m i r r o r e d i n r e a l s e a s , and

o n l y f u r t h e r t ank t e s t i n g w i t h t h e r e q u i r e d d e v i c e c o n f i g u r a t i o n

a l t e r a t i o n s w i l l demons t ra te t h e answer. Thus i t can be s t a t e d

t h a t t h e Team h a s a r r i v e d a t a p o i n t i n i t s t e s t i n g programme i n

which i t i s now a b l e t o s p e c i f y much more e x a c t l y t h e form o f

d e v i c e d e s i r e d f o r t h e nex t s t e p and t h e f u r t h e r more r e f i n e d t e s t s

n e c e s s a r y t o r each a d e s i r a b l e p r o d u c t i v i t y l e v e l .

The c y l i n d e r l e n g t h , s p e c i f i c g r a v i t y , submergence and w a t e r dep th

have been determined f o r a 12m d iamete r c y l i n d e r h u t t h e y a r e

s u b j e c t t o m o d i f i c a t i o n f o r t h e 15 m d i a m e t e r c y l i n d e r . Regarding

l e n g t h i t i s now r e a l i s e d t h a t economic c o n s i d e r a t i o n s cou ld l e a d

t o a l o n g e r c y l i n d e r , s i n c e v i r t u a l l y t h e same v e r y expens ive

rodes ( i n c l u d i n g p i l i n g and i n s t a l l a t i o n ) would t h e n be more

economica l ly u t i l i s e d i n c o l l e c t i n g more power. The c o s t o f t h e

e x t r a l e n g t h of c y l i n d e r would be r e l a t i v e l y smal l . Although

t h e r e i s a drop i n c y l i n d e r c a p t u r e e f f i c i e n c y w i t h i n c r e a s e i n

c y l i n d e r l e n g t h , i n changing from 75m t o 100 m l e n g t h t h e r e i s

n e v e r t h e l e s s a n e t i n c r e a s e i n c a p t u r e d power p e r c y l i n d e r . There

w i l l t h e r e f o r e be a n optimum l e n g t h , which t h e proposed e s t i m a t e

o f 100 m i s gauged t o r e p r e s e n t . However f o r t h e p r e s e n t

a s s e s s m e n t , a l e n g t h o f 75m i s used s i n c e a l l e f f i c i e n c y

c a l c u l a t i o n s and c o s t i n g s r e f e r r e d t o t h i s .

C a ~ t u r e E f f i c i e n c i e s

The Device Team h a s p r e s e n t e d a range of scheme mean annual d e v i c e

c a p t u r e e f f i c i e n c i e s depending on which o f t h e i r p r e d i c t e d

improvement f a c t o r s a r e i n c l u d e d i n t h e e f f i c i e n c y c a l c u l a t i o n ,

and whether t h e c y l i n d e r remains a t i t s a s - t e s t e d l e n g t h of 75m o r

cur ren t ly -p roposed l e n g t h of 100m. These a r e a s fo l lows :

1981 Design V a r i a b l e Tuning V a r i a b l e Tunins

(F ixed t u n i n g ) (12m d i a m e t e r ) (15m d i a m e t e r )

75m long c y l i n d e r 39% 49.4% 65%

10Om long c y l i n d e r 32.8% 41.6% 56.5%

The c o r r e s p o n d i n g number of d e v i c e s i n a 2GW scheme a r e a s fo l lows

75m long c y l i n d e r 615

1OOm long c y l i n d e r 5 18

The C o n s u l t a n t s have c a l c u l a t e d cor respond ing f i g u r e s us ing t h e

Team's t ank r e s u l t s , b u t i n t e r p r e t i n g t h e e f f e c t o f t h e miss ing

wave components d i f f e r e n t l y from t h e Team a s they b e l i e v e t h e Team

h a s o v e r e s t i m a t e d t h i s e f f e c t . There is a l s o a d i f f e r e n c e between

t h e Team and the C o n s u l t a n t s i n t h e c a l c u l a t i o n o f t h e a v a i l a b l e

power. The C o n s u l t a n t s have a l lowed t h e same p r e d i c t e d pe rcen tage

improvements a s t h e Team f o r f r i c t i o n and d r a g l o s s e s i n t h e r i g ,

unequal rode s t i f f n e s s e s , v a r i a b l e t u n i n g and l o n g e r c y l i n d e r , and

they have a l s o used t h e same l o s s o f e f f i c i e n c y r a t i o i n changing

from a 75m t o lO0m long c y l i n d e r . The C o n s u l t a n t s t h u s o b t a i n t h e

f o l l o w i n g mean annua l c a p t u r e e f f i c i e n c i e s :

1981 Design Variable Tuning

Fixed Tuning (12m diameter)

75m long cylinder 28.6%

lOOm long cylinder 24.1%

and the following numbers of devices in a 2GW scheme

75m long cylinder 720

lOOm long cylinder 606

Variable Tuning

(15m diameter)

Status of Assessment Data

Simple idealised calculations, acceptable for the state of

development reached, have been completed for the cylinder itself,

the anchor piles, and the power take-off system.

The basic design and constructional details of the major

structural elements of this device are well advanced and the

Device Team has provided information on quantities and cost

estimates for certain special items which have been checked

whenever practicable and used as a basis for the Consultants' cost

estimate. The Device Team has also provided a preliminary

structural cost estimate which in total appears to be within 1% of

the Consultants' own estimate, but it should be noted that the cost

of the cylinder itself is less than 10% of the cost of the scheme.

The Team's advisers have provided comprehensive estimates for the

platform generating equipment, transformers and switchgear. The

only modification made by the Consultants is the additional cost

of the inlet manifold. The electrical collection and transmission

circuit^ have also been costed by the Team to which has been added

the cost of the Skye terminal plant. These estimates have been

accepted in part For budgetary purposes but the Consultants are of

the opinion that the costs of submarine cabling and line

construction are considerably underestimated. Furthermore some

cost centres are omitted.

'Che i n s t a l l a t i o n c o s t s have been dpvt~Loprt l i n ~ ~ a t - a l l ~ l by t h e

C o n s u l t a n t s and t h e Team and t h e i r a d v i s e r s and t h e r e i s now v e r y

good agrsernent be tween them on i n s t a l l a t i o n c o s t s f o r b o t h p i l e s

and c y l i n d e r .

Ma in tenance c o s t s have been p r o v i s i o n a l l y a s s e s s e d by t h e

C o n s u l t a n t s i n advance o f f i n a l i n f o r m a t i o n f rom t h e Device Team,

YARD and EASAMS.

I t s h o u l d be no ted t h a t a l l c o s t i n g t~ d a t e h a s been c a r r i e d o u t

assuming 12n d i a m e t e r c y l i n d e r s . The change t o 1 5 m d i a m e t e r w i l l

a l t e r r o d e and p i l e d e s i g n s and t h e r e f o r e c o s t s , a s w e l l a s a l t e r

c o s t s o f t h e c y l i n d e r i t s e l f , and i t s i n s t a l l a t i o n and

mai-ntenance. The a l t e r a t i o n came t o o l a t e f o r r e - c o s t i n g t o be

c a r r i e d o u t f o r t h i s r e p o r t i n d e t a i l , b u t a nominal 15% i s added

t o t h e a f f e c t e d i t e m s .

Development

The Team h a s pu r sued a r i g o r o u s , q u e s t i o n i n g approach t o a l l

a s p e c t s (,E t h e d e v i c e , w i t h t h e a i d o f .3 l a r g e team o f sub-

c o n t r a c t o r s , e x p e r i e n c e d i n t h e i r r e s p e c t i v e f i e l d s . The p r o c e s s

o f development i n e v i t a b l y i n v o l v e s i d e n t i f i c a t i o n o f new problems,

l e a d i n g t o a d o p t i o n o f a l t e r n a t i v e s o l u t i o n s . T h i s h a s been t h e

c a s e i n t h i s p r o j e c t , p a r t i c u a r l y f o r t h e power t a k e - o f f sys t em,

t h e r o d e s and t h e i n s t a l l a t i o n sys t em, which a r e a l l i n t e r -

r e l a t e d .

Tn sp i t . . o f r x p l o r i n g o t h e r o p t i o n s f o r power t a k e - o f f , t h e d e v i c e

h a s r e t a i n e d i t s p r e s e n t form s i n c e i t s i n c e p t i o n . The c y l i n d e r

l e n g t h had p r e v i o u s l y i n c r e a s e d i n August 1981 from 50m t o 75m i n

o r d e r t o accomodate s i x moor ing r o d e s i n s t e a d o f f o u r t o p r o v i d e

r o d e redundancy i n t h e e v e n t o f a r o d e f a i l u r e . O t h e r w i s e , r e c e n t

a l t e r a t i o n s can a l l be c l a s s e d a s development o f d e s i g n d e t a i l s

r a t h e r t h a n a 1 t e r a t i o n s .

R e c e n t l y , t h e Tearn f o c r ~ s s e d i t s a t t e q t i o n on t h e p o s s i b i l i t y o f

r is ing "tube-pumps" i n p l a c e o f t h e mechan ica l s p r i n g s c o m p r i s i n g

p i s t o n s and a c c u m u l a t o r s , which t h e y have s o f a r deve loped f o r t h e

rodes i n t h e b e l i e f t h a t they ought t o use o n l y e x i s t i n g , proven

technology. (The term " t ~ b e - ~ u m ~ " i s be ing used a s t h i s i s i t s

adopted name from o t h e r s i t u a t i o n s , b u t t h e B r i s t o l Team s e e s i t s

use i n t h e i r d e v i c e s imply a s a s p r i n g , s i n c e i t s s i n g l e a c t i n g

pumping behav iour would n o t be s u i t a b l e f o r t h e i r power o f f t a k e

system. 'tlowever s i n c e each rode c o n t a i n s s i x s p r i n g s and two

pumps, f i n a n c i a l s a v i n g i n u s i n g e l a s tomeric t u b e s f o r s p r i n g s

could be s u b s t a n t i a l , s i n c e t h e r o d e s a r e t h e major c o s t c e n t r e i n

t h i s d e v i c e ) . The a d o p t i o n of tube s p r i n g s , b e s i d e s e f f e c t i n g a

r e d u c t i o n i n c a p i t a l c o s t , would l ead t o e a s i e r (and c h e a p e r )

i n s t a l l a t i o n , s i m p l e r (and c h e a p e r ) end c o n n e c t i o n s and s i m p l e r

and cheaper replacement . P r o v i d i n g f u t u r e development can prove

i t s long term performance and r e l i a b i l i t y , and Avon Rubber

Company's c o s t e s t i m a t e s a r e c o r r e c t , t h i s component o f f e r s a v e r y

a t t r a c t i v e improvement i n t h i s d e v i c e .

F o r t h e ptlrposes o f t h i s a s sessment t h e r e f o r e , tube s p r i n g s

c o s t i n g E 1 M p e r d e v i c e have been assumed w i t h a co r respond ing

r e d u c t i o n i n t h e t e l e s c o p i c tube f l e x i - j o i n t s c o s t s a s proposed by

t h e Tearn. I t shou ld be a p p r e c i a t e d t h a t t h i s i s an e s t i m a t e made

w i t h o u t r edeve lop ing t h e e n g i n e e r i n g d e t a i l s o f i n s t a l l a t i o n , end-

c o n n e c t i o n s , f a t i g u e l i f e , and r e d e s i g n e d rode and anchor f o r c e s ,

b e s i d e s not a1 lowing f o r t h e e n g i n e e r i n g o f v a r y i n g s p r i n g and

darnping r a t e s .

The subsea n a t u r e o f t h e d e v i c e i s a t the same t ime bo th an

advantage and d i s a d v a n t a g e . The advantage i s t h a t i t i s no t

s u b j e c t t o t h e v i o l e n t e f f e c t s o f extreme s e a s and f r e a k waves.

Rode f o r c e s i n f a c t reduce i n t h e s e a s t h e c y l i n d e r i s de-tuned.

L i m i t i n g f o r c e s and d i s p l a c e m e n t s a r e t h e r e f o r e known and can be

des igned f o r w i t h some conf idence . The d i s a d v a n t a g e o f

i n a c c e s s i b i l i t y i s r e f l e c t e d i n h i g h c o s t of i n s t a l l a t i o n and

maintenance (which u s u a l l y means r e p l a c e m e n t ) , and r e l i a b i l i t y .

However t h e v u l n e r a b l e components below t h e s e a a r e r e l a t i v e l y few

( t h e pump, i t s o u t l e t v a l v e , t h e rode s p r i n g s , and s e a bed

pipework). The major p a r t o f t h e power c o n v e r s i o n p l a n t i s on t h e

p l a t f o r m , w e l l above wa te r l e v e l and e n c l o s e d i n a c o n t r o l l e d

environment and f u l l y main ta ined i n t h e same way a s a c o n v e n t i o n a l

hydro-power s t a t i o n .

The i n t e r a c t i o n w i t h YARD i s c o n t i n u i n g , b u t t h e Team h a s

i d e n t i f i e d t h a t t h e assumpt ions made BY YARD concern ing r e l a t i v e l y

minor components ( such a s t h e number of p i s t o n s e a l s , t h e type o f

accumulator b l a d d e r ) make a dominant e f f e c t on t h e r e s u l t i n g

r e l i a b i l i t y of t h e o v e r a l l scheme. They a r e t h e r e f o r e c o n f i d e n t

t h a t f u t u r e i n t e r a c t i o n w i t h YARD w i l l e n a b l e them t o show an

a c c e p t a b l e r e l i a b i l i t y . I n t h e meantime, t h e C o n s u l t a n t s a r e

us ing an assumed r e l i a b i l i t y f a c t o r o f 0 .8 .

The major mar i t ime i n s t a l l a t i o n o p e r a t i o n s w i l l be c r i t i c a l l y

s u b j e c t t o t h e wea the r , and i n o r d e r t o i n s t a l l enough d e v i c e s i n

good wea the r , a l a r g e amount o f expens ive p l a n t and manpower w i l l

have t o be a v a i l a b l e , which f o r much o f t h e t ime w i l l be o n l y

w a i t i n g f o r good wea the r . There i s a major t e c h n i c a l r e s e r v a t i o n

on t h e d u r a b i l i t y o f t h e p e l t o n t u r b i n e and n o z z l e s i n s e a w a t e r ;

t h e r e arc3 no d a t a , p r a c t i c a l o r r e s e a r c h , t o i n d i c a t e t h e l i k e l y

performancp a t t h e ve ry h i g h j e t v e l o c i t y proposed.

I d e n t i f i c a t i o n of a s u i t a b l e bucket and nozz le m a t e r i a l must be

the s u b j e c t of f u t u r e r e s e a r c h . I n p r i n c i p l e however the power

t ake -of f and t r a n s m i s s i o n t o Skye a r e e n t i r e l y f e a s i b l e .

The r e l a t i v e l y l e n g t h y submarine c a b l e s r e q u i r e d t o o p e r a t e a t 275

kV and 400 ItV would need t o be c o n s t r u c t e d w i t h a polymeric

i n s u l a t i o n i n o r d e r t o reduce r e a c t i v e c u r r e n t r equ i rements . Such

c a b l e s a r e now b e i n g developed anc! should be a v a i l a b l e when

r e q u i r e d . The seabed r o u t e s have no t been i d e n t i f i e d . There a r e

known t o be d i f f i c u l t i e s west o f t h e Oute r H e b r i d e s , b u t t h i s

d e s i g n f o r t u n a t e l y minimises t h e number of i n d i v i d u a l c a b l e r o u t e s

r e q u i r e d and does n o t r e q u i r e f l e x i b l e c a b l e s .

Apar t from doubts o v e r t h e t u r b i n e b u c k e t s and n o z z l e s , t h e

C o n s u l t a n t ' s t e c h n i c a l r e s e r v a t i o n s a r e :

i ) The f a t i g u e l i f e o f h e a v i l y loaded rode components.

T h i s shou ld not be an i n s u p e r a b l e problem w i t h c a r e f u l d e s i g n .

5 / ( i ) / 8

C o r r e c t d o s i n g and f i l t r a t i o n t r e a t m e n t shou ld overcome t h i s .

i i i ) I n t e g r i t y o f t h e h y d r a u l i c t r a n s m i s s i o n p i p e s .

The tendency of t h e p i p e s t o move under t h e h i g h i n t e r n a l f o r c e s

and t o c o r r o d e a t p i p e weld f l a w s i n t h e s a l t w a t e r environment

impose a v e r y s e v e r e d u t y on t h e p i p e l i n e . S u i t a b l e p i p e bedding

and anchorage , and c o r r o s i o n p r o t e c t i o n a r e v i t a l .

i v ) p r o v i s i o n f o r p i p e l i n e p r e s s u r e r e l i e f i n t h e e v e n t o f a

sudden drop i n e l e c t r i c a l load .

D e t a i l s o f t h e mechanism f o r t h i s have not been worked o u t b u t t h e

Team e n v i s a g e s a u t o m a t i c blow-off v a l v e s i n t h e main, d i s c h a r g i n g

d i r e c t i n t o t h e s e a . The s t a b i l i t y of t h e h y d r a u l i c sys tem i s i n

some doubt due t o t h e absence o f any h y d r a u l i c s t o r a g e on t h e h i g h

p r e s s u r e s i d e o f t h e system.

v ) P r o v i s i o n f o r t h e i s o l a t i o n of branch mains , i . e . o f

i n d i v i d u a l d e v i c e s i n t h e e v e n t o f a b ranch p i p e f a i l u r e .

The need f o r t h i s i s r e c o g n i s e d b u t t h e d e t a i l s o f r emote ly

o p e r a t i n g t h e n e c e s s a r y v a l v e s have n o t been worlced o u t .

v i ) The f l e x i b l e p i p e c o n n e c t i n g t h e rode pumps t o t h e s e a bed

main.

An e x i s t i n g product des igned t o c a r r y h igh p r e s s u r e f l u i d ( a t up t o

28,000 p s i ) e x i s t s Eor use i n t h e o i l i n d u s t r y b u t behav iour under

t h e d u t y r e q u i r e d h e r e i.s unknown and w i l l have t o be proved.

v i i ) Mechanical wear of t h e pump chamber, ist tons, and v a l v e s .

The d u t y r e q u i r e d i n s e a w a t e r i s o n r r o u s . Although I n c o n e l 625

c l a d d i n g h a s been a l lowed on t h e p i s t o n rods t h e d u r a b i l i t y of t h e

whole sys tem should be s u b j e c t t o d e t a i l e d d e s i g n and development.

( v i i i ) The i n s t a l l a t i o n o f t h e s e a bed power c o l l e c t i o n mains by

towing o u t l o n g l e n g t h s ( a p p r o x . 5km) and s i n k i n g i n one p i e c e on a

p r e p a r e d bed on t h e rocky f l o o r i s bound t o be a d e l i c a t e o p e r a t i o n

r e q u i r i n g ca lm c o n d i t i o n s . Wl~ar ton-Wil l iams r e p o r t t h a t a 2km

l e n g t h o f 36 i n c h d i a m e t e r p i p e h a s been towed 393 km f o r

i n s t a l l a t i o n i n t h e Nor th Sea and t h e y c o n s i d e r l e n g t h s o f 10 km t o

b e f e r l s i h l e . The main d i f f e r e n c e o f f t h e H e b r i d e s i s t h e n a t u r e o f

t h e s e a bed and t h e amount o f bed p r e p a r a t i o n n e c e s s a r y t o a v o i d

f i n a l d e f o r m a t i o n t h e p i p e , and t o p r e v e n t i t moving d u r i n g

s e r v i c e .

C o n c l u s i o n s

As i n d i c a t e d above t h e d e v i c e r ema ins a t a n i n t e r i m s t a g e o f

development . The f u r t h e r model t e s t i n g p l anned i n 1982 airns t o

s u b s t a n t i a t e t h e improvements i n pe r fo rmance p r e d i c a t e d i n r e a l

s e a s . The ma jo r c o s t c e n t r e i s t h e r o d e s ( w i t h t h e f l e x i b l e j o i n t s

making a v e r y l a r g e c o n t r i b u t i o n a c c o r d i n g t o SBMs f i g u r e s , b u t

t h e Team's own i n v e s t i g a t i o n s w i t h Dunlop l e a d t o a s u b s t a n t i a l

r e d u c t i o n ) . The Team i s t h e r e f o r e v i ewing t h e f u t u r e development

o f t u b e s p r i n g s w i t h g r e a t i n t e r e s t .

The p r e s e n t a s s e s s m e n t l e a d i n g t o a c o s t o f 10.2p/kWh i s t h e r e f o r e

based on a d e s i g n f o r which r e l e v a n t model t e s t s and c o s t i n g s

s t u d i e s have n o t been done i n a n y t h i n g l i k e t h e d e t a i l o f t h e

p r e v i o u s 1981 r e f e r e n c e d e s i g n (which had t h e p a r a m e t e r s l2m

d i a m e t e r , 7 5 , l o n g , f i x e d t u n i n g and mechan ica l s p r i n g s ) . T h i s

c o s t o f power i s t h e r e f o r e dependen t on t h e Team's many

a s s u m p t i o n s b e i n g conf i rmed by morp d e t a i l e d s t u d i e s i n t h e

f u t t l r e , t h e s e shou ld i n c l u d e m a t e r i a l and e n g i n e e r i n g development

o f t h e t u b e s p r i n g s and end c o n n e c t i o n s , r e d e s i g n o f t h e d e v i c e and

a n c h o r s Eor d i f f e r e n t r o d e f o r c e s , new power t a k e - o f f pump,

t e l e s c o p i c t u b e and f l e x i j o i n t a r r a n g m e n t s , t a n k - t e s t i n g w i t h t h e

new p a r a m e t e r s , new i n s t a l l a t i o n p r o c e d u r e s and c o s t s , and

m a t e r i a l s t u d i e s f o r t h e P e l t o n Wheel b u c k e t s .

LANCASTER FLEXIBLE BAG

LANCASTER FLEXIBLE BAG

A R R A Y A N D L Q C A T t o h l

WAVE FALLlrJG - WC O P E ~ I N G WAJE RtSlrJG - BAG CLoscdG

WORKING CYCLE

A . Rela t cd t o Locat ion

1. Distorlcc o f f s h o r e (km)

2 . Wntcr dep th (m)

3 . Power i n s e a (Kw/ni)

L Re la t ed t o d e v i c e

1. O v e r a l l s i z e - l e n g t h (m)

- b r e a d t h (m)

- v c r t i c a l dimension (m) 2 - g r o s s c r o s s s e c t i o n a l a r e a (m )

2 . Weight of d e v i c e ( t o n n e s )

3 . Weight of d e v i c e G l e n g t h (torrlieslm)

C . Rc l a t cd t o 2GW s ~ ~ l *

1 . Nuwber of d e v i c e s

?. Spacing of d e v i c c s (m)

2 . LcnzLh of 2GW s t i i t i n n (km! ( c s c l . nav ig . gaps )

U . Re l a t ed t o procl i l r t i \ , i tp

1. Roting of Cc1Ieratul.s (!l:.i)

2 . Power i n s e a (1:wlm)

5 . 5 and 2 . 5 t+w/device

50.8

1.35

0.48

3 . Elcnn annua l power d c l i v e r c d t o Skye ( !~f~~/ ' i ievice)*

4 . Elcan annu;ll o u t p u t of 2GW schcrnc (C\,:)*

8 . Rela t cd t o s t r u c t ~ l r c econon~y an11 u t i l i z a t i o n of r c s o o r c e p---p-.- -

1. Eleon annua l power d e l i v e r e d p e r d e v i c e f lengLir of dc'ricc (K'd/rn)*

L. Meail :rnnilal power del iverer1 pe r d e v i c e F dcv i ce spac ing (Kw/m)*

3 . O v e r a l l conve r s ion efficiency o f sciiernc"

r~iean annua l o u t p u t of ?(;Is schcnie (2) lrlcarl oiinti;il power i n s e a S l e n g t h of 2Gl i s t a t i o n

mcart annu;ll power cnpt11rc,d by rii?vicc (7;) - -. p - -. - - 111c;iir nnnunl power i n sc,i ;; d c v i c e I cng th

F . Rclotc-il t t , c o s t

1 . Cost of ?Gi4 s t a t i o n ( ~ l r i ( ~ i s c n u ~ t t e d ) (C?!)

2 . Cost <,I' r ach d e v i c e ( u n d i s c n ~ ~ n t c d ) (CPI)

3. Cost ul' energy ( d i s c o u n t e d ) (p/Kwli)

C.. f l i s c c l l a ~ i ~ ~

1. ?lean nn ru~a l powrtr cha in c f f i c i c r r c ; ( X ) * * ' :

2 . , \ v a i l n b i l i t y of t h e 2GW sciirriie ( X )

3.

* i nc l r i d ing n v n i l a b j l i ty f a c t o r

** n o t i n c l u d i i ~ p , .ivai l a b i l i ty f a c t o r

*** mean nnri:ial p n ~ i c r lanclcd n t Skye . -- ( n o t i n c l u d i n g a v a i l a b i l i t y f a c t o r ) !:lean annua l power cop tu rcd p e r d e v i c e x No. of d e v i c e s i n scheme

LANCASTER FLEXIBLE BAG

General

The LFB as presented by t h e cu r r en t re ference design i s a f i n a l

s t a g e i n the evo lu t ion of t he f l e x i b l e bag device which began with

Prof . French 's conceptual design of 1 9 7 7 . Prof . French attempted

t o develop the concept on the b a s i s . of 4 c a r d i n a l cons i d e r a t ions

which were:

i ) To provide very cheap s imple working i n t e r f a c e with the

waves ( a rubber bag).

i i ) To maximise the r a t i o of swept volume t o s t r u c t u r a l volume

of the device. This being i d e n t i f i e d a s an e s s e n t i a l

parameter fo r an economic design.

i i i ) To func t ion a s an a t t e n u a t o r r a t h e r than a terminator:

f i r s t l y because i t was seen t o be e a s i e r t o s t a b i l i s e a sp ine

spanning across t he c r e s t s and secondly because it i s

e s s e n t i a l f o r the device t o experience both wave c r e s t s and

troughs s imultaneously, w i th in the f i n i t e length of t h e

device.

i v ) To adopt low p res su re a i r a s t h e i d e a l medium f o r power o f f -

take.

S t a t u s of Assessment Data

The b a s i c sp ine des ign and c o n s t r u c t i o n a l d e t a i l i n g a r e a t an

advanced s t a g e and t h e Device Team has provided information on

q u a n t i t i e s and cos t es t imates f o r c e r t a i n s p e c i a l items which have

been checked and used a s a b a s i s f o r t h e Consul tan ts ' c o s t

es t imate . The Consul tants i n i t i a l cos t es t imate , using t h e

r e spec t ive working paper was not i n agreement with t h e Team's

f i gu res . The two s u b s t a n t i a l d i f f e r e n c e s were i n r a t e s f o r

concre te and post- tensioning. In both these a r eas t h e Device Team

designed f o r ease of cons t ruc t ion , not n e c e s s a r i l y t o minimise

q u a n t i t y . I n o r d e r t o pe rmi t c l o s e r c o r r e l a t i o n w i t h o t h e r

d e v i c e s , t h e Team's lower c o s t i n g r a t e s have been used t o

compensate f o r t h i s ' o v e r d e s i g n ' . The r e d u c t i o n i n c o s t stemming

from t h i s is o f t h e o r d e r o f 1.25pIkWh.

Very l i m i t e d machinery c o s t s have been r e c e i v e d from t h e Device

Team b u t r a t h e r more b u t s t i l l incomple te c o s t i n f o r m a t i o n on t h e

t r a n s m i s s i o n i s a v a i l a b l e . The c o n s u l t a n t s have used mainly t h e i r

own c o s t i n g s f o r mechan ica l p l a n t and c a b l i n g . The c o s t i n g s f o r

p l a n t a r e s p e c u l a t i v e b u t a r e though t t o a l l o w c o r r e l a t i o n w i t h

o t h e r a i r d e v i c e s .

The i n s t a l l a t i o n c o s t s have been developed by t h e C o n s u l t a n t s and

a s s e s s e d a g a i n s t t h e Dev ice Team's r e p o r t . The maintenance c o s t s

have been developed by t h e C o n s u l t a n t s and compare c l o s e l y w i t h

those r e c e i v e d from t h e Dev ice Team a l t h o u g h t h e r e i s some

v a r i a t i o n i n approach.

Development

I n 1 9 7 8 t h e d e v i c e was t e n t a t i v e l y a s s e s s e d a s a good p r o s p e c t , b u t

on t h e b a s i s o f v e r y l i m i t e d i n f o r m a t i o n b o t h i n r e s p e c t of

s t r u c t u r a l s i z e and p r o d u c t i v i t y . Loss through l o c a l bag f a i l u r e

and t h e d i f f i c u l t i e s o f d e s i g n i n g a s u i t a b l e bag were i d e n t i f i e d

a s problem a r e a s .

The p r e s e n t d e s i g n h a s , f o r t h e f i r s t t ime, had t h e b e n e f i t o f

wide-tank f r e e f l o a t i n g t e s t i n g and a thorough s t r u c t u r a l

e n g i n e e r i n g development. The changes t h a t have t a k e n p l a c e s i n c e

c o n c e p t i o n have been s p e c i f i c a l l y : -

i ) Development o f d i s c r e t e a i r c e l l s i n p l a c e o f t h e con t inuous

bag.

T h i s change h a s l i t t l e e f f e c t on t h e swept volume b u t

p e r m i t s a c r e d i b l e bag d e s i g n and reduces t h e damage c o n t r o l

problem.

i i ) Development o f h u l l geometry around t h e bags t o p r o v i d e a

s t a b l e r e f e r e n c e frame of a d e q u a t e s t r e n g t h .

The r e s u l t o f t h i s work h a s been t o i n c r e a s e s i g n i f i c a n t l y

t h e s t r u c t u r a l volume wi th a c o n s e q u e n t i a l economic p e n a l t y .

The p r o d u c t i v i t y o f a l l subsequen t v a r i a t i o n s o f t h e d e v i c e d u r i n g

development h a s been below t h a t measured f o r t h e o r i g i n a l

c o n c e p t u a l "bag a l o n g t h e top" d e s i g n . Not a l l t h e r e a s o n s f o r t h i s

a r e thoroughly unders tood b u t they c e r t a i n l y i n c l u d e l o s s o f power

through s p i n e mot ion and t h e "nowhere t o go" f e a t u r e o f any

manifolded d e v i c e w i t h l i m i t e d r e s e r v o i r volume. I t is a l s o c l e a r

t h a t t h e Device Team i s on ly a t an e a r l y s t a g e o f u n d e r s t a n d i n g t h e

hydrodynamics o f t h e d e v i c e and t h e c u r r e n t d e s i g n may b e f a r from

o p t i m a l .

A comparison w i t h t h e Clam i s i n e v i t a b l e and i s u s e f u l i n

h i g h l i g h t i n g s t a g e s i n t h e development which now appear

c o u n t e r p r o d u c t i v e . The o r i g i n a l concept was a double-s ided bag

o v e r a c o n c r e t e s p i n e . To pe rmi t a n e n g i n e e r i n g s o l u t i o n t h e bag

was f i r s t s p l i t i n t o two s t r i p bags-one a l o n g each s i d e o f t h e

d e v i c e - and was s u b s e q u e n t l y s p l i t f u r t h e r i n t o d i s c r e t e bag

p a n e l s . The r e s u l t o f t h e independent Clam development, f o r q u i t e

d i f f e r e n t r e a s o n s , has ended w i t h what c a n be termed t h e o r i g i n a l

French concept of a d o u b l e s i d e d bag, b u t subd iv ided i n t o

manageable l e n g t h s and then mounted on - one s i d e of t h e s p i n e . The

s i g n i f i c a n t r e s u l t o f t h i s i s t h a t t h e bag p i e r c e s t h e wa te r p l a n e

and t h e s p i n e can be d e s i g n e d independen t ly w i t h o u t t h e

requ i rement o f a p a s s i v e r e a r f a c e t o t h e bag c e l l . The

consequence i s much-improved n a t u r a l s t a b i l i t y o v e r t h e LFB and a s

a r e s u l t t h e s t r u c t u r a l s p i n e o f t h e Clam can be economical ly

des igned a s a r e f e r e n c e frame t o c a r r y wave induced f o r c e s .

Although doub le - s ided , t h e LFB i s n o t o r i e n t a t e d a s a p u r e 0 a t t e n u a t o r . More power was absorbed by i n c l i n i n g t h e d e v i c e a t 30

- 40' t o t h e predorninent wave d i r e c t i o n . The r e a s o n s f o r t h i s a r e

no t y e t f u l l y a p p a r e n t b u t i t seems t h a t i n mixed s p r e a d s e a s ,

d e s i g n o f a p u r e a t t e n u a t o r is i m p o s s i b l e and t h e optimum d e v i c e

o r i e n t a t i o n i s between t e r m i n a t o r and a t t e n u a t o r .

The f l e x i b l e membrane system i s extremely c o s t e f f e c t i v e a s an

i n t e r f a c e w i t h t h e waves. The bags have been f u l l y developed and

w i t h c o n t i n u i n g r e s e a r c h , p a r t i c u l a r l y i n t o i n t e r p l y f a t i g u e , long

l i f e shou ld be proved.

The r e f e r e n c e frame h a s been des igned comprehensively and t h e

load ings assumed a r e r e a l i s t i c and p o s s i b l y c o n s e r v a t i v e . The

d e s i g n o f t h e s p i n e however could be f u r t h e r pursued t o reduce t h e

weight by up t o 1 5 % .

The o r i e n t a t i o n o f t h e LFB a t t e n u a t o r h a s l e d t o asymmetric power

o f f t a k e r a t i n g s . Valve and d u c t d e s i g n has been f u l l y

i n v e s t i g a t e d and t h e t u r b i n e i s r e l a t i v e l y c o n v e n t i o n a l and w i t h i n

p h y s i c a l d e s i g n l i m i t a t i o n s . P l a n t d e s i g n h a s been s t u d i e d

i n d u s t r i a l l y and i s a t an advanced s t a g e , though G.E.C. have no t

y e t p r e s e n t e d t h e i r r e p o r t .

The power p l a n t i s r e l a t i v e l y c o n v e n t i o n a l and n o t approaching

p h y s i c a l d e s i g n l i m i t a t i o n s . The a l t e r n a t o r , however, i s a

v a r i a b l e speed machine f e e d i n g a s e r i e s d.c. load. A s p e c i a l

e x c i t a t i o n sys tem i s r e q u i r e d i n v o l v i n g r o t a t i n g t h y r i s t o r s and

t h i s w i l l need development .

Conc l u s ions

The o v e r a l l r e s u l t o f t h e development a t p r e s e n t i s ve ry

d i s a p p o i n t i n g t o a l l concerned and t h e c o s t p e r Kwh is t o o h igh .

Although some c o s t r e d u c t i o n s may be p o s s i b l e on t h e s p i n e and

moorings, i t is c e r t a i n t h a t t h e d e v i c e has major b u i l t - i n c o s t

impediments i n i t s p r e s e n t form which p r e v e n t i t being a

s u c c e s s f u l con tender . The development o f p r a c t i c a l a t t e n u a t o r s i s

r e a l l y s t i l l i n i t s in fancy and t h e theory i s n o t y e t f u l l y

unders tood. L a n c a s t e r a r e c o n t i n u i n g w i t h development of

a t t e n u n t o r s and have made s i g n i f i c a n t p r o g r e s s s i n c e t h e i r d e v i c e

was eng ineered i n t o i t s p r e s e n t form by WPL. WPL themselves a r e

t u r n i n g t h e i r a t t e n t i o n t o a bottom-mounted a l t e r n a t i v e .

NEL BOTTOM STANDING TERMINhTOR

-

OWC- BOTTOM STANDING-.NELl TERMINATOR

LOCATION OF S C H E M E

D I M E N S I O N S

W A V ~ F A L L I W C ; WAVE R I J ~ ~ C

B l A GRArnMhTt c REPRESBWTATls 14 QF o P ~ R A T I ~ G CYCLE

LEADING ULVICE PARAMETERS

(Loca t ion - S o i j ~ h U i s t )

NEI. BOT'rOI.1 STANDING TI:RMINATOR

11. Rela t ed t o - 1 ~ 1 ~ 1 ~ i ~ t ~ ~

1 . I)i!;t;lnce o f f s h o r e (km)

2 . Water dep th (m)

1. Power i n s e a (Kwlm)

B. Re l a t cd t o d e v i c e

1. Overcl11 s i z e - lcngt l i (m)

- b r c ; ~ d t h (m)

- v c r t i c a l d imension (m) 2 - g r o s s c r o s s sectional a r e a (m )

2 . Weight of dev i ce ( t o n n e s )

3 . Weight of d e v i c c l eng th ( tonneslm)

C . Rc l a t ed t o 2GW s t a t i o n

1 . Numbcr nf d e v i c e s

2. Spacirig of d e v i c e s (m)

3 . L e n e t l ~ of 2GIJ s t a t i o n (km) ( e x c l . n a v i g . gaps )

D . Rc l a t ed t o p r o d u c t i v i t y

1. R a t i ~ t g of ~ e ~ ~ c r a t o r s (MW) 3 X 1 . 5 5 Mwldevice

2 . Power i n s c a (Kwlm) 2 9 . 6

3 . M ~ ; I I I a nnua l power d e l i v c r r d t o Skye (Mw/dcvice)* 0 . 6 8 8

4 . Meall nnnunl o u t p u t of 2GW schc:ne (CW)" 0 .406

E . Re l a t cd t o s t r u c t u r e ceonomy and u t i l i ~ a t i o ~ n of re sour^

1 . Mean annual power d e l i v c r c d p e r d e v i c e t l e n g t h of dev i ce (Kw/m)*

2 . Mean annua l power d e l i v e r e d pc r d e v i c c ' d e v i ~ c spac ing (Kw/m)*

3 . O v c r a l l conve r s ion c f f i c i r t n c y of scheme*

mean a n l ~ u a l o u t p u t of 2614 scheme p----

( 9 ) mean annua l power i n s e a x l e n g t h of 2Gl4 < t a t i o n

4 . Cap tu re Factor**

mean annua l power cap tu red by d e v i c e (%) mean annua l power i n s e a X d e v i c e l e n g t h

F . Re l a t ed t o cost-

1. Cost of ICU s t a t i o n ( i~nd i scou t i t ed ) (£!I)

2 . Cost of each devictl ( und i scoun ted ) (EM)

3. Cost c~ f cncryy ( d i s r o u ~ ~ t ~ d ) (pIKwli)

C. ~ i s c e l l a n c o u s

1. Mean a ~ r n u a l power cl>ai,n e f f i c i e n c y (X)***

2 . A v a i l a b i l i t y of t h e 2GW scheme (7 . )

3 .

4 .

* i n c l u d i n g a v a i l a b i l i t y f a c t o r

** n o t i n c l u d i n g a v a i l a b i l i t y f a c t o r

*** mean annua l power landed a t Skye (no t i n c l u d i n g a v a i l a b i l i t y f a c t o r ) mean annua l power cap tu red p e r d e v i c e X No. of d e v i c e s i n scheme

5 ( i i i ) a ) NEL BOTTOM STANDING TERMINATOR

1. GENERAL

1 . l DESIGN

The s t r u c t u r a l c a l c u l a t i o n s f o r t h e d e v i c e a r e based on t h e

methods developed f o r t h e A t t e n u a t o r i n accordance w i t h t h e

OWC Note 30 and t o a p p r o p r i a t e and a c c e p t a b l e d e s i g n c r i t e r i a .

The Device Team' S d e s i g n ph i losophy i s f u l l y a c c e p t a b l e t o t h e

C o n s u l t a n t s .

The Device Team i s u n d e r t a k i n g a comprehensive a n a l y s i s o f

s t r u c t u r a l e f f e c t s due t o wave load ing . While i t i s accep ted

t h a t f u r t h e r work i s r e q u i r e d on t h i s l o a d i n g c a s e , t h e

C o n s u l t a n t s b e l i e v e t h a t any r e s u l t i n g m o d i f i c a t i o n s t o t h e

s t r u c t u r e found t o be n e c e s s a r y w i l l have a n i n s i g n i f i c a n t

a f f e c t on c o n s t r u c t i o n c o s t s .

The i n s t a l l a t i o n p rocedure , i n which t h e 3 - c e l l u n i t i s

o f f e r e d up t o 9 s t a b b i n g g u i d e s p r e - s e t on t h e sea-bed i s

c o n s i d e r e d by t h e C o n s u l t a n t s t o be a r e a s o n a b l e e x t e n s i o n of

accep ted e n g i n e e r i n g p r a c t i c e .

N o d i f i c a t i o n s t o t h e d e s i g n d i s c u s s e d i n t h i s Note a r e

examined i n S e c t i o n 4.

TANK TESTING

The 21m mark I1 d e v i c e h a s n o t i t s e l f been t a n k - t e s t e d . The

p r o d u c t i v i t y r e s u l t s provided a t t h i s s t a g e by NEL a r e based

on a s i m u l a t e d mathemat ica l model u s i n g a t h e o r e t i c a l

monochromatic e f f i c i e n c y curve . It i s emphasised t h a t t h e

o u t p u t o f t h i s computer programme u s i n g t h e monochromatic

c u r v e was compared w i t h t h e r e s u l t s from t h e September Cadnam

t a n k t e s t s f o r t h e 25 m mark I d e v i c e and agreement was

o b t a i n e d . The Device Team i n t e n d s t o u n d e r t a k e t h e

a p p r o p r i a t e t e s t i n g i n t h e Cadnam Tank f o r t h e 46 s p e c t r a a t a n

e a r l y d a t e and t h i s i s n e c e s s a r y b e f o r e r e s u l t s can b e

expressed w i t h con£ idence .

The t h e o r e t i c a l a n a l y s i s , shows t h a t t he device has a

hydrodynamic e f f i c i e n c y of 6 1 . 9 % , comparing favourably with

va lues obtained f o r t h e f l o a t i n g terminator of 25%.

SPECIFICATION

This i s broadly based on t h e NEL Reference Design 1980

( ~ R 2 2 : ~ a v e 00) and on NEL summary of M and E P l an t Rating and

P roduc t iv i ty 8 t h January 1982. Close l i a i s o n has been

maintained between t h e Device Team and Consul tants on the

development of t h e above.

Due t o on-going modi f ica t ions t o t he des ign , a s discussed

l a t e r , t h e Device Team has not y e t produced a formal

s p e c i f i c a t i o n .

COSTING

F u l l co-operation has been maintained between the Device Team

and t h e Consul tants on cons t ruc t ion c o s t s , and so f a r a s

poss ib l e , i n view of des ign changes, on i n s t a l l a t i o n cos t s .

Good agreement has been reached a t a l l times on information so

f a r obtained .

A formal p re sen ta t ion of cos t ing f o r t he device has not y e t

been provided by t h e Device Team f o r the reasons s t a t e d under

1 . 3 and summarised i n Sec t ion 4.

DEVELOPMENT

GENERAL

The concept of a bottom mounted device fol lows n a t u r a l l y from

an assessment of d i f f i c u l t i e s a s soc i a t ed with mooring

i n s t a l l a t i o n i n t he c a s e of f l o a t i n g devices . The long term

maintenance of such moorings and o the r f a c t o r s a l l suggest

t h a t t he reduced power cap tu re p o t e n t i a l due t o l oca t ion i n

shal lower waters i s more than compensated by ease of

maintenance and of gene ra l access a s we l l a s enabling t h e

s t r u c t u r a l d e s i g n t o be based on a more c o n v e n t i o n a l

breakwater phi losophy. The Refe rence Design 1980, r e f e r r e d t o

above, examines t h e c a s e o f a breakwater d e v i c e c o n t i n u o u s l y

mounted on t h e s e a bed a t d e p t h s o f 1 5 - 20m w i t h a concomitant

reduced c a p t u r e p o t e n t i a l .

Subsequent ly t h e Device Team i n v e s t i g a t e d a module based on

t h e 25 m dep th and founded on p i l e d p l i n t h s . Although good

c a p t u r e was achieved t h e i n s t a l l a t i o n p rocedure was expensive

mainly due t o t h e high c o s t o f t h e p i l i n g , and t h e Team h a s

t h e r e f o r e moved t h e d e v i c e t o 21 m d e p t h , e l i m i n a t i n g t h e need

f o r p i l i n g and producing a more e f f e c t i v e d e s i g n .

MANIFOLDING

I n June and J u l y o f 1981 t h e concept o f j o i n i n g t h r e e 4 - c e l l

u n i t s and mani fo ld ing t h e a i r f low t o one o r two AC power u n i t s

was examined by t h e Device Team. The Team a n t i c i p a t e d a

smoothed power i n p u t , s i m p l e r p l a n t r equ i rements and reduced

d e v i c e t o s h o r e t r a n s m i s s i o n producing u s e f u l economies w i t h

s m a l l c a p t u r e l o s s . The r e s u l t s o f t ank t e s t i n g i n September

d i d n o t suppor t t h i s . The system d i s c u s s e d i n t h i s n o t e

t h e r e f o r e comprises a 1 :l c e l l t o t u r b i n e j g e n e r a t o r r a t i o .

The p o s s i b i l i t y o f mani fo ld ing i s s t i l l be ing examined.

PLINTHS AND ROCK ANCHORS

I n o r d e r t o reduce t h e amount o f s e a bed p r e p a r a t i o n i n h e r e n t

i n t h e o r i g i n a l 1980 scheme a s w e l l a s t o e n a b l e t h e d e v i c e t o

be l o c a t e d i n deeper w a t e r , t h e Device Team decided i n

February 1981 t o s u p p o r t t h e modules on c o n c r e t e p l i n t h s , two

per f o u r - c e l l u n i t and i n 25 m dep th o f wa te r . The

i n s t a l l a t i o n of t h e p l i n t h s p r i o r t o t h e module emplacement

c r e a t e d some engi 'neering d i f f i c u l t i e s which, a l though l e s s

onerous t h a n t h o s e a p p l y i n g t o t h e o r i g i n a l b reakwate r d e s i g n

were s e e n by t h e Design Team and C o n s u l t a n t s a s r e p r e s e n t i n g

an unaccep tab ly h i g h c o s t c e n t r e .

I n t h e l i g h t o f t h e above, t h e Team examined t h e p o s s i b i l i t y o f

i n t e g r a t i n g t h e p l i n t h s wi th t h e modules and a l s o o f a v o i d i n g

t h e u s e o f p i l i n g by a d o p t i n g rock anchor ing t echn iques . The

proposed rock anchor system c o n s i s t i n g o f 57 No. 1 9 / 1 8 Dyform

tendons i s t o a proven d e s i g n and h a s t h e n e c e s s a r y s a f e t y

margins a g a i n s t s h e a r and o v e r t u r n i n g .

CHANGES TO DEVICE PROFILE

The 1980 Reference Design shape was e s s e n t i a l l y square i n

c r o s s s e c t i o n , g i v i n g a h i g h r e a c t i o n a r e a t o wave f o r c e s . The

c u r r e n t d e s i g n a s d e t a i l e d i n drawing R B / 1 0 , August 1981 is

streamed on t h e seaward f a c e w i t h a th ickened nose s e c t i o n and

a smoothed run-over s e c t i o n f o r d i m i n i s h i n g t h e e f f e c t s o f

wave load ings . I n t h e l a t e s t d e s i g n a l l s p a r e s t r u c t u r e which

i s n o t s p e c i f i c a l l y used i n wave c a p t u r e h a s been minimised.

FEASIBILITY

The C o n s u l t a n t s c o n s i d e r t h e Bottom Stand ing Terminator OWC

concept t o be f e a s i b l e . Moreover t h e scheme envisaged

p o s s e s s e s t h e n e c e s s a r y d e g r e e o f ruggedness combined w i t h

r e l a t i v e l y easy maintenance d u e t o s e l f s h e l t e r and proximity

t o shore .

As compared t o t h e 1980 OWC d e s i g n , t h e concept o f s u p p o r t i n g

t h e modules on s t a b b i n g gu ides c a l l s f o r g r e a t e r accuracy a s

r e g a r d s l o c a t i o n b u t over a s m a l l e r sea-bed a r e a . The

proposed c o n s t r u c t i o n and i n s t a l l a t i o n p rocedures p r e s e n t no

n o v e l eng ineer ing f e a t u r e s . I n summary, t h e s t a b b i n g gu ides

a r e i n s t a l l e d and rock anchored i n advance o f embedment. The

modules a r e t r a n s f e r r e d from c o n s t r u c t i o n yard t o s i t e u s i n g

a d d i t i o n a l buoyancy f o r s k i d l aunch ing and f o r lock ing down on

t o t h e s t a b b i n g g u i d e s ( 9 p e r module). Once s o l o c a t e d ,

lock ing mechanisms i n t h e g u i d e s ho ld t h e module f i r m l y w h i l e

buoyancy i s r e t a i n e d . Under t h e s e c o n d i t i o n s , i . e . b e f o r e t h e

remaining rock anchors i n t h e s t r u c t u r e a r e i n s t a l l e d , t h e

s t a b b i n g gu ides p r o v i d e an ample margin o f s t r e n g t h a g a i n s t

s h e a r and o v e r t u r n i n g . It i s t h e i n t e n t i o n o f t h e d e v i c e team

t o g r o u t benea th t h e d e v i c e b e f o r e t h e remaining rock anchors

a r e d r i l l e d and i n s t a l l e d .

The proposed system o f rock anchor ing o u t l i n e d above is based

on e s t a b l i s h e d and a c c e p t a b l e p r a c t i c e .

The maximum f o r c e s c a r r i e d p e r d e v i c e a r e 282 T/M h o r i z o n t a l

and 74 T/M v e r t i c a l . The rock anchor ing system prov ides

a c c e p t a b l e m a t e r i a l and load s a f e t y f a c t o r s t o s u s t a i n t h e

above.

The C o n s u l t a n t s b road ly a c c e p t t h e c o n s t r u c t i o n t iming

sequence o f 8 y e a r s sugges ted by t h e Device Team.

CONCLUSIONS

I n a g r e e i n g w i t h t h e Device Team's c o s t i n g and programme

e s t i m a t e s and i n r e c o g n i s i n g t h e proposed s t r u c t u r a l d e s i g n o f

t h e module a s be ing a r e a s o n a b l e one, i n v o l v i n g no s i g n i f i c a n t

e x t r a p o l a t i o n o f c u r r e n t e n g i n e e r i n g p r a c t i c e s , t h e

C o n s u l t a n t s conf i rm t h a t t h e Bottom Stand ing Terminator i s an

a c c e p t a b l e d e v i c e . Both t h e C o n s u l t a n t s and t h e Device Team

acknowledge t h a t f u r t h e r work i s r e q u i r e d a s r e g a r d s

o p t i m i s i n g t h e i n s t a l l a t i o n p rocedure and i n ' t u n i n g ' o u t t h e

wave load i n g s .

The new 21 m d e s i g n h a s e l i m i n a t e d t h e need f o r s e p a r a t e

p l i n t h s and avoided t h e u s e o f p i l i n g - a h i g h c o s t c e n t r e .

The a d o p t i o n of a x i a l - f l o w t u r b i n e s and g e n e r a l m o d i f i c a t i o n s

t o t h e geometry o f t h e d e v i c e h a s produced a compact system

o f f e r i n g good cos t - sav ing p o t e n t i a l a l l i e d w i t h a s i m p l i f i e d

embedment procedure .

VICKERS TERMINATOR

OWC -BOTTOM .STANDING-vICKER'S' TERM1 NATOR

t t t t

LEADING D E V I C E PARAMETERS p--.----

(I.oc.?tion - So11tl1 U i s t )

VTCKERS 'II:R?I INATOR ----p-

A . Rela t ed ro l o c a t i o n

1. D i s t a n c e o f f s h o r e (km)

2 . Water dep th (m)

3. Power i n s e a (Kw/m)

B . Re l a t ed t o d e v i c

1. O v e r a l l s i z e - l e n g t h (m)

- b r e a d t h (m) l - v e r t i c a l d imension (m)

2 - g r c s s c r o s s s e c ~ i o n a l a r e a (m )

2. Weight of d e v i c e ( t onnes )

3 . Weight of d e v i c e I l e n g t h ( tonneslm)

C. Re l a t ed t o 2GU s t a t i o n

1. Number of d e v i c e s

2 . Spacing of d e v i c e s (m)

3 . Length of 2GW s t a t i o n (km) ( e x c l . n a v i g . gaps)

D . Re1 l t c d t o product-

1. Ra t ing of g e n e r a t o r s (MW) 7 x 4 . 2 MW p e r 10 d e v i c e s

2 . Power i n s ea (Kw/m) 3 6 . 2

3 . Elean ~ n n u a l power delivered t o Skye (Mw/device)* 0 . 4 6 4 . Mean annua l o u t p u t of 2Gi.i scheme (CV)* 0 .50

E. Re l a t ed t o s t r u c t u r e economy and ut i l iz&oi~ of r c s o u r c e

1. blcan annual. power de l i ve rc t l pe r d e v i c e f len$:th oE d e v i c e (Kw/m)*

2 . F1c.m anntinl porscr d c l i v e r c d pcr c l e ~ ~ i c r I dev ice s p a c i n g (Kwim)*

mcan nrinual o u t p u t of 2CW scheme -- ( 9 ) mcan annua l power i n sc.1 X l c n g t h of ?G!: s t a t i o n

4 . Capture Paceor*:'(

mcan annu?-wer c a p t ~ t r e d by dev i ce (%) mean annua l power i n s e a x d e v i c e l e n g t h

F . R e l a t e d t o cos:

l Cost o f ZGW s t a t i o n (undiscoui i tcd) (£M)

2. Cost of each d e v i c e (und i scoun tcd ) (EM)

3 . Cost of energy ( d i s c o u n t e d ) (p/Xwh)

C. Mi sce l l aneous

1 . Menn annua l powcr r h a i n e f f i c i e n c y (X)***

2 . A v a i l a b i l i t y of t h e 2GW scheme ( X )

3.

* i n c l u d i n g a v a i l a b i l i t y f a c t o r

** n o t i nc lud inc : n v a i l a h i l i t y f a c t o r

*** ineon annua l power landed a t Skye mean annua l power cdp tu rcd p e r d e v i c c X No. of device., i n scherne

( n o t i n c l u d i n g a v a i l a b i l i t y f a c t o r )

VICKERS TERMINATOR

General

The p r o d u c t i v i t y d a t a f o r t h e c u r r e n t r e f e r e n c e d e s i g n have been

o b t a i n e d u s i n g a 1 /200th s c a l e model i n t h e wide t ank a t Wave Power

L td . , Cadnam. These d a t a a r e somewhat s u s p e c t b e c a u s e of t h e s m a l l

s c a l e of t h e t e s t model and t h e f a c t t h a t t h i s was t h e f i r s t d e v i c e

t o be t e s t e d i n t h e modif ied 46 s p e c t r a r e p r e s e n t i n g t h e 25m wate r

d e p t h ; some of which were l a t e r found t o b e i n c o r r e c t l y

t r ans fo rmed . The Team h a s a t t empted t o modify t h e exper imenta l

v a l u e s which a r e now approx imate ly c o n s i s t e n t w i t h comparable

a t t e n u a t o r r e s u l t s b u t must s t i l l be t r e a t e d w i t h c a u t i o n .

The C o n s u l t a n t s have r e c e i v e d t h r e e s t r u c t u r a l d rawings , a scheme

l a y o u t , a p r e c a s t i n g drawing and t h e General Arrangement.

Although some thought a p p e a r s t o have been g i v e n t o d imensioning

t h e members, no w r i t t e n d e t a i l s o f t h e s t r u c t u r a l d e s i g n have been

r e c e i v e d by t h e C o n s u l t a n t s . The c o n s t r u c t i o n , t r a n s p o r t a t i o n and

i n s t a l l a t i o n o f t h e d e v i c e have been covered i n a s e p a r a t e r e p o r t .

The C o n s u l t a n t s have been asked t o a s s e s s a r e v i s e d i n s t a l l a t i o n

p rocedure based on c o s t s a v i n g s ach ieved by t h e Team's C o n s u l t a n t s

i n t h e i r work on t h e NEL Breakwater d e v i c e . No d e t a i l s have been

r e c e i v e d b u t t h e i n s t a l l a t i o n c o s t s have been c a l c u l a t e d i n

p r o p o r t i o n t o t h e NEI, d e v i c e .

The mechanical and e l e c t r i c a l p l a n t i n f o r m a t i o n r e c e i v e d from t h e

Team i s f o r t h e a t t e n u a t o r d e v i c e r a t h e r than t h e t e r m i n a t o r b u t

t h e power o f f t a k e i s unders tood t o be s i m i l a r . The equipment f o r

t h e a t t e n u a t o r d e v i c e h a s been s p e c i f i e d i n c o n s i d e r a b l e d e t a i l

w i t h drawings and diagrams. The e l e c t r i c a l d e s i g n h a s been f a i r l y

w e l l deve loped ; more s o t h a n t h e mechanical . The d .c . s e r i e s

method o f power a g g r e g a t i o n from t h e d e v i c e s h a s been fo l lowed ,

t h e s w i t c h g e a r , i s o l a t i o n t r a n s f o r m e r s and r e c t i f i e r s be ing

accommodated i n t h e c e n t r a l p l a n t room where c o n d i t i o n s w i l l be

good and a c c e s s r e a d i l y a v a i l a b l e . The t u r b i n e i s l o c a t e d i n a

r a t h e r more h o s t i l e environment a t approx imate ly 2 a tmospheres

p r e s s u r e and s e a l e d o f f from t h e p l a n t room. Access f o r

maintenance can be o b t a i n e d e i t h e r by c l o s i n g t h e i s o l a t i o n v a l v e s

o r by s e a l i n g and p r e s s u r i s i n g t h e p l a n t chamber.

S t a t u s of Assessment Data

The b a s i c d e s i g n o f t h e major e lements o f t h e c i v i l works

a s s o c i a t e d wi th t h i s d e v i c e i s a t an advanced s t a g e and t h e Team

h a s provided p r e l i m i n a r y i n f o r m a t i o n on q u a n t i t i e s and c o s t s which

have been independen t ly checked and found t o be a c c u r a t e t o w i t h i n

about 1% of t h e t o t a l d e v i c e c o s t . The only major d i f f e r e n c e

between Device Team and Consu l tan t s i n t h e s t r u c t u r a l c o s t c e n t r e s

is over t h e type o f f a c i l i t y t o be used. The Team h a s assumed a

s i n g l e l a r g e f a c i l i t y which t h e Consu l tan t s a g r e e would lead t o a

c o s t s a v i n g o f 0.2p/kwh i f cons idered p r a c t i c a b l e .

The p l a n t and t r a n s m i s s i o n d e s i g n i s now reasonab ly w e l l d e f i n e d .

The C o n s u l t a n t s o r i g i n a l l y i n c o r p o r a t e d t h e i r own assessment o f

t h e p l a n t c o s t s and a r e l i a b i l i t y a n a l y s i s i n t o t h e i r c o s t

f i g u r e s . The r e l i a b i l i t y a n a l y s i s was based on f a i l u r e r a t e s

g iven by Y-ARD, and a l though t h e Team's comments on t h e power c h a i n

model have been i n c o r p o r a t e d , t h e C o n s u l t a n t s have n o t a l t e r e d t h e

b a s i c d a t a . The Team subsequen t ly provided t h e i r own c o s t i n g

which s u b s t a n t i a l l y a g r e e s w i t h t h e Consu l tan t s i n a l l b u t two

i tems: t h e t u r b o g e n e r a t o r s e t and t h e t r a n s m i s s i o n scheme. The

c o s t o f t h e t u r b o g e n e r a t o r has now been reso lved and t h e c u r r e n t

c o s t e s t i m a t e s r e v i s e d . However, t h e Consu l tan t s have r e c e n t l y

r e v i s e d upwards t h e c o s t o f a l l t h e Teams ' t r a n s m i s s i o n schemes.

Th is g i v e s an i n c r e a s e of 62% over t h e p r e v i o u s l y agreed f i g u r e ,

a l though t h e C o n s u l t a n t s c o n s i d e r t h a t t h e Team could recoup

approximately 18% ( 0 . 2 p/kwh) by r e d e s i g n i n g t h e t r ansmis S i o n

scheme.

The o r i g i n a l i n s t a l l a t i o n procedure s p e c i f i e d by t h e Device Team

was checked by t h e C o n s u l t a n t s who e s t i m a t e a c o s t approximately

0.2pIkwh h i g h e r than t h e Teams. However t h e c o s t o f m a t e r i a l s used

i n t h e i n s t a l l a t i o n was n o t agreed f o r t h i s procedure . The

C o n s u l t a n t s have r e v i s e d t h e i r c o s t i n g o f t h e d e v i c e i n s t a l l a t i o n

programme i n l i n e w i t h t h e s i m i l a r NEL breakwater d e v i c e and have

e s t i m a t e d a s a v i n g o f 0.55pIkwh over t h e o r i g i n a l method. However

f a c e breakwa

he dep th of W

?board a r e

; ing t h e b r e a

n t ed d e v i c e s ,

i o n of c u r

l l o w i n g d e t ~

r e £ l e c t o r .

ind t h e s t a t

Dn programme,

t o p rov ide a

moment S .

~ b t a i n e d f ror

t h e Team ha:

h t h e Consul

:hod o f e x c i t

l i t a b i l i t y .

i n c r e a s i n g

~ l e f o r t h e

.y s e l f a c t u a

formance .

v i i ) An i n h e r e n t d i s a d v a n t a g e w i t h t h e submerged d e v i c e i s t h a t

t h e enc losed a i r i s above a tmospher ic p r e s s u r e and needs a

compressor supp ly - leakage w i l l e v e n t u a l l y f l o o d t h e

t u r b i n e .

Conclus ion

The major c o s t c e n t r e s i n t h i s d e v i c e a r e s t r u c t u r e ( 4 0 % ) , p l a n t

(16%) and i n s t a l l a t i o n ( 3 0 % ) . Because o f t h e ext reme

env i ronmenta l c o n d i t i o n s o f f t h e c o a s t o f South U i s t i t i s

d i f f i c u l t t o conce ive how t h e c o s t o f t h e b reakwate r element of t h e

s t r u c t u r e could be s u b s t a n t i a l l y reduced.

I t i s p o s s i b l e t h a t a s a v i n g i n s t r u c t u r a l c o s t s could be made i n

t h o s e e lements no t loaded by r e f l e c t i n g waves o r b r e a k i n g wave

f o r c e s . The p l a n t d e s i g n and i n s t a l l a t i o n sequence have been w e l l

though t o u t and would seem u n l i k e l y t o y i e l d s i g n i f i c a n t sav ings .

The most l i k e l y s o u r c e of i n c r e a s e d c o s t e f f i c i e n c y would b e a g a i n

i n p r o d u c t i v i t y , e s p e c i a l l y c o n s i d e r i n g t h e s m a l l amount o f work

t h a t h a s been s p e n t o p t i m i s i n g t h e c u r r e n t d e s i g n . It i s a l s o

p o s s i b l e t h a t d u c t l o s s e s and s c a l e e f f e c t s which have been shown

t o c a u s e s i g n i f i c a n t e r r o r s i n t h e a t t e n u a t o r t e s t s could b e

s i m i l a r l y reduced i n t h e t e r m i n a t o r by b e t t e r d e s i g n o f t h e d u c t

bend.

The t h e o r e t i c a l e f f i c i e n c y o f t h i s d e v i c e i n s e a s which do n o t

o v e r t o p t h e r e f l e c t o r i s 100%. Because t h e r e f l e c t o r i s o n l y 2m

above mean s e a l e v e l t h i s r e s t r i c t s t h e maximum e f f i c i e n c y t o s e a s

w i t h wave h e i g h t s of l e s s t h a n 4m. S ince t h e b o r e and s t r o k e of

t h e d e v i c e is l i m i t e d , t h i s o v e r t o p p i n g is a d e s i r a b l e f e a t u r e and

a l s o c o n s i d e r a b l y reduces t h e f o r c e s on t h e d e v i c e . One of t h e

main d i s a d v a n t a g e s o f t h e d e v i c e i s i t s r e l i a n c e on t h e c r e s t -

spanning mode o f o p e r a t i o n which i s imposed by t h e c l o s e d a i r

c y c l e . D e s p i t e l i n k i n g d e v i c e s i n t o 800m long b l o c k s , t h e

C o n s u l t a n t s s u s p e c t t h a t t h i s is one r e a s o n f o r t h e r e l a t i v e l y low

e f f i c i e n c y o f t h e d e v i c e .

One f e a t u r e of t h e d e v i c e is i t s h i g h power a v a i l a b i l i t y because o f

t h e common mani fo lds which connec t seven g e n e r a t i n g s e t s i n

p a r a l l e l . T h i s p e r m i t s 30% of t h e r a t e d c a p a c i t y t o b e l o s t w i t h

o n l y a 10% r e d u c t i o n i n mean annua l power o u t p u t .

PLAN ON e ~ e t ----W OF aEvrtL-2 A R R ~ Y

LEADIN(; D E V I C E I'ARAFlEl'RRS -p--

(Lociltic>n - South Llist)

ii. Rela t ed t o ldc&02

1. Dis t ance o f f s h o r e (km)

2 . [ l a t e r dep th (or)

3 . Power i n s e a (Kwlm)

B . Re l a t ed t o d e v i c e

1. O v e r a l l s i z e - l e n g t h (m)

- b r e a d t h (m)

- v e r t i c a l d imension (m) 2

- g r o s s c r o s s s e c t i o n a l a r e a (m )

2 . Weight of d e v i c e ( t o n n e s )

3 . Wcight of d e v i c e I l e n g t h ( tonneslm)

C. Reca t ed t o LGIJ s t a t i o n

1. Number of dev i ce s

2 . Spacing of dev i ce s (m)

3 . 1,ength of 2CW s t a t i o n (km) ( e x c l . n a v i g . gaps)

u . w e d t o p r o d u c t i v i t y

1. R a t i n g of g e n e r a t o r s (MW)

2 . Yrwer i n s e a (Kwim)

3. Mrnn annual power d e l i v e r e d t o Skye (Mw/device)*

4. Plean annua l o u t p u t of 2CW scheme (CV)*

E . Re l a t ed t o s t r u c t u r e economy and u t i l i z a t i o n of r e s o u r c e

l . Mean annua l power d e l i v e r e d pe r d e v i c e 5 l eng th of d e v i c e (Kw/n)*

2 . Mean a n n u ~ l power d e l i v e r e d p e r rlcvice I g c v i c e s p a c i n g (Kw/m)*

3. O v e r a l l conve r s ion c f f i c i e n c y o f scheme*

mcJn annua l o u t p u t of 2GW schen~e -- ( X ) mean annua l power i n s e a x l e n g t h of 26W s t a t i o n

4 . Capture Factor**

nican i~iinital power yapcured by d e v i c e ( 2 ) nrcnn anr>ual power I n s e a x d e v i c e l e n g t h

F . Re l a t ed t o c o s t

1. Cost of 2GM s t a t i o n (und i scoun tcd ) (EPI)

2 . Cost of each d e v i c e (und i seoun ted ) (:Pi)

3. Cos t of energy ( d i s c o u n t e d ) (p1Kwh)

C . ? i i s c e l l a n c o u s

1. Eleaii annua l powcr c h a i n c f f i c i e n c y (H)***

2 . A v a i l a b i l i t y of tiic 2CW scheme ( I )

* ir icludiny. a v a i l a b i l i t y f a c t o r

** riot i l~c l c rd ing a v a i l a b i l i t y [ a c t o r

*** mean annua l power landed a t Skye -- ( n o t including a v a i l a b i l i t y f a c t o r ) mean annua l power cap tu red p c r d e v i c e x No. of d e v i c e s i n sclieme

5 ( i i i ) c

General

VICKERS ATTENUATOR

A l / l O o t h s c a l e model o f t h e c u r r e n t r e f e r e n c e d e s i g n h a s been

thorough ly t e s t e d i n t h e wide t ank of Wave Power L t d . , Cadnam. The

p r o d u c t i v i t y d a t a were then o b t a i n e d from t e s t s on t h i s and a

1 1 6 7 ~ " s c a l e model of t h e optimum d e v i c e c o n f i g u r a t i o n i n t h e 46

s e l e c t e d I O S s p e c t r a . The 1167 th s c a l e t e s t s i n d i c a t e a much

b e t t e r performance than t h e s m a l l e r s c a l e t e s t s . Th i s i s p a r t l y

due t o a r e f i n e m e n t i n t h e i n t e r n a l geometry o f t h e d u c t and p a r t l y

due t o t h e f a c t t h a t t h e Team has c a l i b r a t e d t h e l a t e r model s o

t h a t t h e o u t p u t power r e a d i n g i n c l u d e s t h o s e l o s s e s which they

e x p e c t t o d i s a p p e a r a t f u l l s c a l e . The C o n s u l t a n t s have agreed t h e

g e n e r a l p r i n c i p l e of t h i s method bu t a r e i n t h e p r o c e s s o f checking

t h e d e t a i l e d a p p l i c a t i o n . U n f o r t u n a t e l y i t h a s been d i s c o v e r e d

t h a t t h e Team was g i v e n i n c o r r e c t i n f o r m a t i o n abou t t h e s p e c t r a i n

t h e wave t ank and a f a c t o r h a s been a p p l i e d t o t h e i r r e s u l t s t o

accoun t f o r t h i s . Although t h e Device Team is c o n t i n u i n g t o r e f i n e

t h e hydrodynamic performance of t h e d e v i c e , t h e b a s i c concept i s

w e l l developed and h a s n o t changed i n t h e l a s t y e a r .

The on ly s t r u c t u r a l drawing r e c e i v e d by t h e C o n s u l t a n t s , a s y e t ,

i s t h e Genera l Arrangement. Although some thought a p p e a r s t o have

been g i v e n t o dimens i o n i n g t h e members, t h e on ly w r i t t e n d e t a i l s

o f t h e s t r u c t u r a l d e s i g n r e c e i v e d by t h e C o n s u l t a n t s r e f e r t o t h e

wave loads . However, i n s t a l l a t i o n and c o n s t r u c t i o n a r e w e l l

documented .

The mechanical and e l e c t r i c a l p l a n t , a n c i l l a r y equipment and

t r a n s m i s s i o n sys tem have been s p e c i f i e d i n c o n s i d e r a b l e d e t a i l

w i t h drawings and diagrams. The e l e c t r i c a l d e s i g n h a s been f a i r l y

w e l l developed - more s o t h a n t h e mechanical . The d.c. s e r i e s

method o f power a g g r e g a t i o n from 4 MW d e v i c e s h a s been fol lowed,

t h e s w i t c h g e a r , i s o l a t i o n t r a n s f o r m e r s and r e c t i f i e r s b e i n g

accommodated i n t h e c e n t r a l p l a n t room where c o n d i t i o n s w i l l be

good and a c c e s s r e a d i l y a v a i l a b l e .

S t a t u s o f Assessment Data

Although t h e b a s i c d e s i g n o f t h e major e lements o f t h i s d e v i c e is

f a i r l y advanced t h e Team have asked f o r s e v e r a l amendments t o t h e

d e s i g n t o be c o n s i d e r e d a t a v e r y l a t e s t a g e . For v a r i o u s r e a s o n s

t h e s e amendments have n o t been p r o p e r l y d e t a i l e d b u t d e s p i t e t h e

u n s a t i s f a c t o r y n a t u r e o f t h e p r e s e n t a t i o n t h e C o n s u l t a n t s have

a t t empted t o i n c o r p o r a t e t h e s e r e v i s i o n s i n t o t h e l a t e s t c o s t

e s t i m a t e s . The c o s t s o f t h e c i v i l a s s o c i a t e d w i t h t h e d e s i g n which

was though t t o b e E ina l a t t h e beg inn ing of January 1982 were

agreed w i t h t h e Device Team. M o d i f i c a t i o n s made t o t h e s h e l l

s t u c t u r e o f t h e d e v i c e have a l s o been c o s t e d and more o r l e s s

ag reed w i t h t h e Device Team. However, t h e m o d i f i c a t i o n t o t h e

c o s t of t h e end s u p p o r t h a s been made u n i l a t e r a l l y by t h e

C o n s u l t a n t s s i n c e i t i s d i f f i c u l t t o e x t r a c t t h e r e q u i r e d f i g u r e

from t h e Dev ice Team's o v e r a l l i n s t a l l a t i o n c o s t .

The p l a n t and t r a n s m i s s i o n d e s i g n is now reasonab ly w e l l d e f i n e d .

The C o n s u l t a n t s o r i g i n a l l y i n c o r p o r a t e d t h e i r own assessment of

t h e c o s t o f t h e p l a n t and a r e l i a b i l i t y a n a l y s i s i n t o t h e i r c o s t

f i g u r e s . The r e l i a b i l i t y a n a l y s i s was based on f a i l u r e r a t e s

s p e c i f i e d by Y-ARD i n a s s o c i a t i o n w i t h t h e power c h a i n s p e c i f i e d

by t h e Team. Th i s f i g u r e h s n o t been modi f i ed . The Team

s u b s e q u e n t l y provided t h e i r own c o s t i n g which s u b s t a n t i a l l y a g r e e s

w i t h t h e C o n s u l t a n t s i n a l l b u t two i t ems : t h e t u r b o g e n e r a t o r s e t

and t h e t r a n s m i s s i o n scheme. The c o s t o f t h e t u r b o g e n e r a t o r h a s

now been r e s o l v e d and t h e c u r r e n t c o s t e s t i m a t e s r e v i s e d . However,

t h e C o n s u l t a n t s have r e c e n t l y r e v i s e d upwards t h e c o s t o f a l l t h e

Teams' t r a n s m i s s i o n schemes. Th i s g i v e s a n i n c r e a s e o f 62% over

t h e p r e v i o u s l y agreed f i g u r e , a l t h o u g h t h e C o n s u l t a n t s c o n s i d e r

t h a t t h e Team could recoup approx imate ly 18% (0.2pIkwh) by

r e d e s i g n i n g t h e t r a n s m i s s i o n scheme.

The i n s t a l l a t i o n c o s t s have been developed by t h e C o n s u l t a n t s w i t h

v e r b a l i n p u t s from t h e Device Team. Subsequen t ly t h e Team h a s

i s s u e d an i n s t a l l a t i o n manual and s e v e r a l amendments which have

been checked by t h e C o n s u l t a n t s and found t o a g r e e i n most

p a r t i c u l a r s . Maintenance c o s t s have been p r o v i s i o n a l l y a s s e s s e d

by t h e C o n s u l t a n t s u s i n g i n f o r m a t i o n from t h e Device Team, YARD

and EASAMS.

Development

Although t h e d e v i c e d e s i g n h a s remained more o r l e s s f i x e d s i n c e

l a t e 1980, two r e c e n t m o d i f i c a t i o n s have been made t o i n c r e a s e i t s

c r e d i b i l i t y and performance. The f i r s t was t o change from a n

a l t e r n a t i n g f low t o a r e c t i f i e d f low scheme w i t h a c e n t r a l p l a n t

chamber and a more c o n v e n t i o n a l u n i - d i r e c t i o n a l a i r t u r b i n e . Th i s

has a l lowed t h e g e n e r a t o r and a n c i l l a r y p l a n t t o b e l o c a t e d i n a

c l o s e d machinery h a l l a t a tmospher ic p r e s s u r e g i v i n g b e t t e r

r e l i a b i l i t y and e a s i e r a c c e s s t o t h e e l e c t r i c a l p l a n t f o r

maintenance. The t u r b i n e i s p r e s s u r i s e d and needs a means o f

i s o l a t i o n . The second change was t o i n c r e a s e t h e bend r a d i u s i n

t h e w a t e r column d u c t . Th i s a l t e r a t i o n h a s been i n c o r p o r a t e d i n t o

t h e new 1 1 6 7 ~ ~ s c a l e model made f o r t h e p r o d u c t i v i t y t e s t s .

F e a s i b i l i t y

The c u r r e n t r e f e r e n c e d e s i g n s t r u c t u r e i s made up o f t h r e e

d i f f e r e n t components, t h e c a i s s o n , t h e o u t e r s u p p o r t s and t h e OWC

c e l l modules, each o f which can be compared t o a s i m i l a r

c o n v e n t i o n a l s t r u c t u r e . The on ly e x t r a p o l a t i o n from c u r r e n t

p r a c t i c e i s t h e i n s t a l l a t i o n o f t h e s e s t r u c t u r e s i n a n exposed

l o c a t i o n . However t h e Team's proposed i n s t a l l a t i o n method h a s

been c o n s i d e r e d i n d e t a i l by t h e C o n s u l t a n t s and t h e c o s t s have

been based on t h e C o n s u l t a n t s ' t iming of each s t e p i n t h e

procedure .

The mechan ica l and e l e c t r i c a l power c h a i n i s r e l a t i v e l y

convent i o n a l . A 1 though a c c e s s t o t h e g e n e r a t o r and a n c i l l a r y

p l a n t i s s t r a i g h t f o r w a r d , t h e t u r b i n e and v a l v e boxes a r e r a t h e r

more d i f f i c u l t t o m a i n t a i n b e i n g s i t u a t e d i n p r e s s u r i s e d a i r .

G e n e r a l l y , however, t h e r e appear t o be no major p r a c t i c a l

d i f f i c u l t i e s invo lved i n t h e c o n s t r u c t i o n , i n s t a l l a t i o n o p e r a t i o n

o r maintenance o f t h i s d e v i c e .

The C o n s u l t a n t s have some r e s e r v a t i o n s abou t d e t a i l e d a s p e c t s o f

t h e des ign . These a r e :

i ) Acknowledged u n c e r t a i n t i e s i n t h e a n a l y s i s o f t h e b reak ing

wave loads on t h e c a i s s o n which w i l l p robab ly r e q u i r e a

model s tudy .

i i ) Loads between t h e c e l l modules and t h e f o u n d a t i o n s d u r i n g

emplacement .

i i i ) The s m a l l t o l e r a n c e s r e q u i r e d on t h e s e a bed p r e p a r a t i o n

under t h e c a i s s o n .

i v ) The r e s i s t a n c e t o s l i d i n g of t h e c a i s s o n s t r u c t u r e . The

C o n s u l t a n t s would p r e f e r t o s e e a d e f i n i t e s h e a r key.

v ) The i n t e r n a l OWC l o s s e s measured by t h e Team a r e v e r y h i g h

and t h e C o n s u l t a n t s would l i k e a more thorough i n v e s t i g a t i o n

o f t h e mechanism o f t h e s e l o s s e s t o e n s u r e t h a t they w i l l n o t

be s i g n i f i c a n t a t f u l l s c a l e .

v i ) The g e n e r a t o r i t s e l f i s c o n v e n t i o n a l b u t t h e Team h a s n o t

adopted b r u s h l e s s t h y r i s t o r e x c i t a t i o n which t h e C o n s u l t a n t s

cons i d e r i s e s s e n t i a l . Furthmore t h e method of e x c i t a t i o n

proposed by t h e Team i s of d o u b t f u l s u i t a b i l i t y . The

C o n s u l t a n t s a l s o c o n s i d e r t h a t t h e speed i n c r e a s i n g b e l t

d r i v e f o r t h e p i l o t e x c i t e r i s u n d e s i r a b l e f o r t h e d u t y

r e q u i r e d .

v i i ) The c e l l a i r v a l v e s a r e l a r g e and a p p a r e n t l y s e l f a c t u a t i n g .

Any l eakage w i l l n u l l i f y column performance.

Conc l u s i o n

The major c o s t c e n t r e s i n t h i s d e v i c e a r e s t r u c t u r e ( 4 2 % ) , p l a n t

(20%) and i n s t a l l a t i o n ( 2 2 % ) . The l a t e s t m o d i f i c a t i o n t o t h e

d e v i c e h a s been t o r educe t h e t h i c k n e s s and s i m p l i f y t h e

c o n s t r u c t i o n of t h e main OWC h u l l s . The Team h a s i n d i c a t e d t h a t i t

would l i k e t o go f u r t h e r and change t h e c o n f i g u r a t i o n of t h e d e v i c e

by r e v e r s i n g t h e f low and p l a c i n g o s c i l l a t i n g wa te r columns a t t h e

o u t s i d e w i t h t h e i n l e t d u c t between them. By t h i s means t h e Team

hope t o i n c r e a s e t h e h u l l s t r e n g t h and d e v i c e e f f i c i e n c y w i t h a

r e d u c t i o n i n t h e q u a l i t y o f m a t e r i a l s r e q u i r e d . Furthmore, by

i n c r e a s i n g t h e swept volume o f t h e d e v i c e t h e Team f e e l t h a t they

would reduce t h e u n i t c o s t a l l o c a t e d t o t h e p l a n t c a i s s o n , p l a n t

module, i n s t a l l a t i o n and t h e c o l l e c t i o n network. The Team

c o n s i d e r t h a t t h e o p t i m i s a t i o n of t h e model s c a l e by which t h i s

d e v i c e was d e f i n e d d i d n o t f u l l y accoun t f o r t h e h i g h f i x e d c o s t s

a s s o c i a t e d w i t h each d e v i c e .

The i n s t a l l a t i o n method h a s a l r e a d y been c o n s i d e r e d i n some d e t a i l

and can on ly be s i g n i f i c a n t l y reduced by e l i m i n a t i n g c e r t a i n key

o p e r a t i o n s which r e q u i r e c o n c e r t e d a c t i o n between d i v e r s and

s u r f a c e p e r s o n n e l . Th i s type of o p e r a t i o n h a s been r e s t r i c t e d t o

lm s e a s t a t e s i n d a y l i g h t and t h e r e f o r e i n v o l v e s a l a r g e amount o f

w a i t i n g t ime f o r t h e e x p e n s i v e i n s t a l l a t i o n p l a n t .

T h i s type o f d e v i c e , b e i n g submerged, can never hope t o be a s

e f f i c i e n t a s a s u r f a c e p i e r c i n g d e v i c e i n p r a c t i c e , a l t h o u g h t h e

t h e o r e t i c a l e f f i c i e n c y o f a n a t t e n u a t o r a r r a y i s 100%. The

C o n s u l t a n t s c o n s i d e r t h a t t h e r e i s some room f o r improvement i n

t h e d e v i c e e f f i c i e n c y and t h a t t h e s t r u c t u r a l c o s t s could s t i l l be

reduced. The main a t t r a c t i o n of a submerged d e v i c e i s t h e lower

f o r c e t o which i t i s s u b j e c t e d . T h i s a l lows o p t i m i s a t i o n of t h e

d e v i c e c o n f i g u r a t i o n w i t h o u t major s t r u c t u r a l c o n s t r a i n t s and t h e

C o n s u l t a n t s c o n s i d e r t h a t some improvements i n t h e d e s i g n ,

i n c l u d i n g an i n c r e a s e i n of t h e swept volume, can s t i l l b e

ach ieved .

BELFAST

3 W C - BOTTOM STANDING- BELFAST PO I NT ABSORBER

LOCATION OF SCHEME

18m.dia. 7 1

€LE V A T l ON ARRAY

DIMENSIONS

h / a d ~ dt;rctt'om __C -

--b. Yi. -' -1-z , - ~ c -- - * P > * -

WAVC R I S I N G WAVE; FALLJNC

W O R K IMG C Y C L E

I.E.4DlNG i)i:VT(:I:. 1'AIUMT:TI:RS - - - - - - --W -- - - - (Locnt ion - Scluth U i s t ) - - . -. . . - - -

I%l<l.FAS'S

A . Rc ln t ed t o l o c a t i o n

1 . D i s t ancc o f f s l i o r e (km)

2. Watcr r l c l ~ t l ~ (m)

3. Powcr i n s e a (Kwlm)

B. Re l a t cd t o d e v i c e

1 . O v e r a l l s i z e - 1eni:th (m)

- b r e a d t h (m) 18m d i ame te r

- v e r t i c a l d imension (m) 5 1 2 - g r o s s c r o s s s e c t i o n a l a r e a (m ) 254

2 . Weight of d e v i c e ( t o n n e s )

3 . Weight of d e v i c e ? l e n g t h ( t onnes im)

C . Re l a t ed t o 2GW s t a t i o n

l . Number of d e v i c e s

2 . Spacing of d e v i c e s (m)

3 . Lengtlr o i 2GW s t a t i o n (km) ( e x c l . n a v i g . gaps )

D . R e l a t e d t o p r t l d u c t i v i t y

1 . Ratin:: o f g e n e r a t o r s (MW) 6 x 0 . 2 5 Mwidcvice

2 . Power i n s e a (Kwlm) 41.7

3 . Elcan annua l powcr delivered t o Skye (PLw/drvicc)* 0 . 2 5

4. Meali ;~rill~i:il o u t p u t of 2 G W scheme ((;IJ)* 0 .48

I:. Re l a t ed t o structure cconomy iinci u t i l i z a t i o n of r e s o u r c c -p- - -

1 . Mcnri . ~ n ~ i u . ? l power- d e l i v e r e d p e r dcvicc? + l eng th of dev i ce (Kw/m)*

2 . Plc:iri nr?n:l;tl powcr d e l i v e r e d p e r d e v i c e + c!evicc spac ing (K1,7/m)*

3 . O v c r a i l coriversiou r [ Eicic,nvy oC achcne*

rnenri :~nntinl ~ , u t p u ~ 01' :'.G\\' :;ch(.rt~c . - - . - - - - - - - -. - - - .- - . (1) Inearl ;rnnunl powt!r i r i :,cc1 7. lcngt.11 01 iCI; !; ta t io i \ .

mean annua l power capturccl l>y d e v i c e ( 9 ) mean annua l powcr i n s e a u rlcvice l c n g t l ~

F. Rela t ed t o c o s t

1. Cost of 2GW s t a t i o n (undiscountc!d) ( E M )

2. Cost of each d e v i c e (und i scoun ted ) ( E M )

3. Cost of cnergy (discounted) (p/Kwh)

G . Mi sce l l aneous

1 . Mc.m .lrrnual powcr c h a i n e t t i c i e n c y ( % ) " * A

2 . A v a i l a b i l i t y of t h e 2GW schcmc ( I )

1900

90m i n a r r a y

85.5

* i n c l u d i n g a v n i l n l ~ i l i t y f a c t 0 1

""lot i n c l u d i n g a v a i l . i b i l i t y f a c t o r

**" mean annua l p ~ i . r e ! _ ~ n t l c c l a t Sky? - -- -- (no t i n c l u d i n g a v a i l a b i l i t y f a c t o r ) mran annua l powPr cap tu red pe r d e v i c e X No. of d e v i c e s h scheme

COST BREAKDOlm 6

f X 10 discounted 2GW Scheme Per 3svice

6 f X 10 undiscounted P------ - 2GW Scheme Per Device

QUEENS UNIVERSITY BELFAST

Structure Construction facility and operation Launch devices Device structure

932.3 C!. $9 96.3 2.05 156.3 (3.08 1184.9 0.62

Valves and ducts Ancillary

Installation Bed reparation Plant and operations

Transmission Generator output to islands Inverters and substations on islands Transmission to Skye

CAPITAL COST 7266.1

Ma i.n t enanc e Maintenance base overheads and operations Vessels, divers and technicians for inspection & repair M & E Spares

MAINTENANCE COSTS 2595.7 --

5 ( i i i ) d QUEEN'S U N I V E R S I T Y , BELFAST DEVICE

The Team h a s c a r r i e d o u t t e s t i n g i n i t s own narrow t a n k and h a s

a l s o worked i n t h e wide t ank a t Edinburgh, producing p r o d u c t i v i t y

r e s u l t s f o r t h e 46 IOS s e l e c t e d s p e c t r a . The Team h a s n o t c a r r i e d

o u t any measurements r e l a t i n g t o wave load ing on t h e d e v i c e .

The C o n s u l t a n t s have n o t r e c e i v e d any c a l c u l a t i o n s o r

s p e c i f i c a t i o n from t h e Team. QUB s a y they have des igned f o r 1 i n

50 y e a r waves and t h a t o u t l i n e c a l c u l a t i o n s f o r t h e s t r u c t u r e ,

c o n s i s t e n t wi th the r a t e o f development, have been made. The

s t r u c t u r e i s a n i n h e r e n t l y s t r o n g shape and should work

s a t i s f a c t o r i l y i n t h e form proposed.

The Team h a s submi t t ed a r e p o r t on c o n s t r u c t i o n and i n s t a l l a t i o n ;

t h e C o n s u l t a n t s g e n e r a l l y a g r e e wi th t h e methods proposed and

c o n s i d e r t h a t they a r e t e c h n i c a l l y f e a s i b l e .

QUB i n t e n d u s i n g s i x Wel ls t u r b i n e s f o r each d e v i c e , coupled t o a

d i r e c t l y d r i v e n 2 5 0 kW g e n e r a t o r . The d e t a i l e d d e s i g n o f t h e

t u r b i n e g e n e r a t o r u n i t and i t s a s s o c i a t e d d u c t i n g h a s r e c e n t l y

been submi t t ed . The Team i s p ropos ing a twin t u r b i n e hav ing two

s t a g e s , mounted on a h o r i z o n t a l a x i s . A s a n a l t e r n a t i v e t o t h e

u s u a l , 4 4 0 V synchronous type a l t e r n a t o r s , QUB a r e a l s o unwisely

c o n s i d e r i n g o p e r a t i n g t h e machine a t f u l l d .c . loop v o l t a g e ,

r e t a i n i n g t h e d i o d e r e c t i f i e r b u t e l i m i n a t i n g t h e t r a n s f o r m e r .

The method o f power c o l l e c t i o n i s t h a t g e n e r a l l y adopted f o r

v a r i a b l e speed g e n e r a t i n g sys tems. Cos t s have n o t y e t been g i v e n

by t h e Team.

S t a t u s o f Assessment Data

The b a s i c d e s i g n and c o n s t r u c t i o n a l d e t a i l i n g o f t h i s d e v i c e a r e

i n o u t l i n e form o n l y and t h e C o n s u l t a n t s ' c o s t e s t i m a t e i s based on

t h e i r own a p p r a i s a l o f t h e l i k e l y form o f t h e c o n s t r u c t i o n a l

d e t a i l s . However, t h e Device Team h a s provided t h e i r own c o s t

e s t i m a t e f o r a s u b s t a n t i a l p a r t o f t h e works which a p p e a r s t o be i n

resonab ly c l o s e agreement wi th t h e C o n s u l t a n t s e s t i m a t e .

The assessment o f t h i s d e v i c e h a s been c a r r i e d o u t u s i n g t h e

C o n s u l t a n t s ' p r e l i m i n a r y e s t i m a t e of t h e e l e c t r i c a l p l a n t c o s t s i n

c o n j u n c t i o n w i t h a c o s t f o r t h e mechanical p l a n t provided by t h e

Team. Cabl ing f o r power c o l l e c t i o n h a s been e s t i m a t e d assuming

S e r i e s i n t e r c o n n e c t i o n o f d e v i c e s and t h e remainder o f t h e

t r a n s m i s s i o n h a s been c o s t e d a s f o r o t h e r s i m i l a r schemes.

The c o s t s o f i n s t a l l a t i o n have been developed by t h e C o n s u l t a n t s

w i t h v e r b a l i n p u t s from t h e Device Team. Maintenance c o s t s have

been p r o v i s i o n a l l y a s s e s s e d by t h e C o n s u l t a n t s i n advance o f f i n a l

i n f o r m a t i o n from t h e Device Team, YARD and EASAMS.

The r e f e r e n c e d e s i g n under c o n s i d e r a t i o n h a s m a i n t a i n e d , s i n c e i t s

i n c e p t i o n i n 1977, t h e p r i n c i p l e s of a p o i n t a b s o r b i n g o s c i l l a t i n g

wa te r column d e v i c e . I t u s e s a i r d r i v e n Wells t u r b i n e s .

Throughout, t h e Team's phi losophy h a s been t o keep t h e d e v i c e

s imple , bo th i n terms o f s t r u c t u r e and power t a k e o f f . Development

h a s been aimed a t improving and o p t i m i z i n g performance, p r i m a r i l y

by means o f p a r a m e t r i c hydrodynamic s t u d i e s and fundamental

r e s e a r c h i n t o improved Wells t u r b i n e c h a r a c t e r i s t i c s .

The major change t o s i x c e l l s was made i n January 1981. The

d e c i s i o n t o bottom mount t h e d e v i c e was made i n August 1981

fo l lowing i n i t i a l wide t ank t e s t i n g i n Edinburgh and t h e form o f

t h e r e f e r e n c e s t r u c t u r e was f r o z e n i n November 1981.

F e a s i b i l i t v

Using a m u l t i s t a g e t u r b i n e n e c e s s i t a t e d by column damping

requ i rements w i l l add t o t h e c o s t and complexi ty o f t h e power t a k e

o f f . Other teams have found t h a t i n l e t g u i d e vanes ( b i -

d i r e c t i o n a l ) improve performance: t h i s may be a l s o t h e c a s e f o r

t h e B e l f a s t Device. The d e s i g n o f a s i n g l e s t a g e t u r b i n e provided

by t h e Team's i n d u s t r i a l a d v i s e r s appears t o be e n t i r e l y

p r a c t i c a b l e , a l though performance under s imula ted wave c o n d i t i o n s

needs t o b e i n v e s t i g a t e d . The p r o p o s a l t o o p e r a t e t h e g e n e r a t o r a t

d . c . sys tem v o l t a g e s a v e s l i t t l e c o s t and i n v o l v e s a l a r g e r

machine and probably a h i g h e r e l e c t r i c a l f a i l u r e r a t e .

The key a r e a s o f t h e s t r c l c t u r a l d e s i g n which r e q u i r e f u r t h e r

deve l opment a r e :

i ) d e s i g n o f t h e p i l e t o c a i s s o n j o i n t ; no d e t a i l s o f t h i s have

been p roposed . The a r e a i s h i g h l y s t r e s s e d and i m p o r t a n t t o

t h e i n t e g r i t y o f t h e s t r u c t u r e . The c o n n e c t i o n h a s t o be

made unde r w a t e r . KPT c o n s i d e r t h a t a s u i t a b l e d e s i g n f o r

t h i s j o i n t c a n be made.

i i ) d e s i g n and development o f a s emi - submers ib l e jack-up

d r i l l i n g v e s s e l c a r r y i n g t h r e e o r s i x d r i l l h e a d s . A v e s s e l

o f t h i s t y p e i s r e q i r e d by most o f t h e b o t t o m s t a n d i n g

d e v i c e s and RPT do n o t q u e s t i o n t h e f e a s i b i l i t y o f t h e

c o n c e p t .

C o s t s

The Team h a s s u b m i t t e d c o s t s f o r c i v i l c o n s t r u c t i o n and

i n s t a l l a t i o n ; t h e s e f i g u r e s a r e i n g e n e r a l ag reemen t w i t h t h e

c o s t s e s t imated by t?ir Cons111 t a n t s . The ~ o n s n l t a n t s ' c o s t s a r e

based on 1900 d e v i c e s t o be c o n s t r u c t e d o v e r a 10 y e a r p e r i o d .

Based upon t h e i r l a t e s t p r o d u c t i v i t y f i g u r e s , t h e Team c a l c u l a t e d

t h a t 1336 d e v i c e s a r e r e q u i r e d t o f u l f i l t h e 2 GW scheme

r e q u i r e m e n t , b u t R P r have i n s u f f i c i e n t i n f o r m a t i o n t o v e r i f y t h i s .

Conc l u s i o n

T h e r e i s no doub t t h a t t h e B e l f a s t Dev ice i s t e c h n i c a l l y f e a s i b l e

i n a l l r e s p e c t s , and a p r o t o t y p e c o u l d be c o n s t r u c t e d and

i n s t a l l e d u s i n g t e c h n i q u e s a l r e a d y p roven . The b a s i c c o n c e p t i s

r o b u s t and s h o u l d prove r e l i a b l e . The Device i s n o n - d i r e c t i o n a l

and n e c e s s a r i l y over-p1 a n t e d .

The C o n s u l t a n t s s h a r e w i t h t h e Team t h e v iew t h a t t h e r e i s

cons i d e r a b l e s cope f o r deve lopmen t o f t h e d e v i c e , which i n i-ts

p r e s e n t form h a s o n l y been s t u d i e d f o r a few months . QUB i s a iming

a t h a l v i n g t h e c o s t o f power i n t h e s h o r t t e rm by a c o m b i n a t i o n o f

improved p r o d u c t i v i t y and by h a v i n g an o p t i m i z e d s t r u c t u r a l s i z e .

The most impor tan t a r e a f o r development is on p r o d u c t i v i t y which

t h e Team admits i s d i s a p p o i n t i n g l y low, due l a r g e l y t o t h e d e v i c e

hav ing t o o low a r e s o n a n t p e r i o d . F u r t h e r narrow tank t e s t i n g i s

c u r r e n t l y be ing performed, s t u d y i n g p r i m a r i l y t h e r e s u l t s of a

v a r i a t i o n o f t h e J - tube e n t r a n c e a n g l e .

The Team h a s s t u d i e d o p t i m i z a t i o n of t h e s t r u c t u r a l and

i n s t a l l a t i o n c o s t s , t a k i n g i n t o accoun t t h a t a b i g g e r d e v i c e w i l l

c a p t u r e more power, p a r t i c u l a r l y i n t h e longer p e r i o d waves. Th i s

s t u d y showed t h a t c o s t was a lmost independent of s i z e and

t h e r e f o r e t h e Device s i z e h a s n o t been changed. F u r t h e r

o p t i m i z a t i o n s t u d i e s could a l s o be made on t h e d e p t h below w a t e r

l e v e l o f t h e p i l e / c a i s s o n j o i n t .

I n t h e longer term, i t w i l l be n e c e s s a r y f o r t h e Team t o c a r r y o u t

wide t ank t e s t i n g on a r r a y s o f p o i n t a b s o r b e r s i n o r d e r t o o p t i m i z e

spac ing and t o improve t h e r e s o u r c e u t i l i z a t i o n , which a t t h e

moment i s low. The Team c o n s i d e r s t h a t more i n f o r m a t i o n on t h e

v a r i a t i o n o f a v a i l a b l e energy w i t h d e p t h must be o b t a i n e d b e f o r e

meaningful s t u d i e s on d e p t h o p t i m i z a t i o n can be c a r r i e d o u t .

NEL FLOATING TERMINATOR

OWC-SPI NE FLOAT1 NG -NEL TERMINATOR L 2 4 kB1

I -- -- 2 6 3 . m -

f ' r eda$s* \ - . . t t f w a v e d I ~ Q L ~ \ o ~ , PLAN ON FLOAT\NG M Q D U L E

WAVE FALLIMG WAVE RISI dG

D1 AGRAMMPTc REPRESENTATION OF O P E R A ~ l t d 4 CYCLE: .

LEADING IIEVICE PARAMETERS -- (Loca t ion - !;out\\ U i s t )

N.E.L. 1:LOh'TINf: TIZHMINATOR

A . Rela t ed t o l o c a t i o n

1 . D i s t , ~ n c c o f f s h o r e (km)

2 . Water dep th (m)

D. Powcr i n s e a (KwJm)

3 . Rela t ed t o d e v i c e

1. O v c r ; ~ l l s i z e - lengl-h (m)

- b r e a d t h ( m )

- v e r t i c a l dinlension (m) 19 2 - g r o s s c r o s s s e c t i o n a l a r e a (m ) 532

2 . Weight oC ~ i c v i c e ( t o n n e s ) 66000

1. Weigiit of J c v i c c + l e n g t h (tonncs/tn) 251

2 . Spacillg oE dev i ce s (111)

3 . 1.cngth ~f 2GM s t n t i o r ~ (km) ( e x c l . 17avig. 8 . 1 ~ ~ )

n. l < e l a t e l t o p r o d u c t i v i t y

1. R.itinp, of g e n e r a t o r s (Elw)

2 . Povcr i n s e a (Kwlm)

3 . Mcau nnrur;il power d e l i v e r e d t o S1:yc (Mw/device)* 2 . 1 1

4 . Mean annua l o u t p u t of 2CW schci!!c ((; id)* 0.389

E . _Rciaivd t u s t r u c t . u r e ocol1umv and u t i l i z a t i u 1 1 U E rcsorircc:

l . Ple;ln nnriu.11 power d c l i v c r e d p e r dcvii-c + l eng th o f i levice ( ~ v l r n ) "

2 . Picnn :int~u.rl power ~ l e l i v e r e d ;irr i levicc f d e v i c , ~ spac ing (Kw/m)*

3. Ovc rn l l conve r s ion c f f i c i c i l c y of r,cl~cnie*

mean annual o u t p u t of 2CId s ~ h ~ -- ( X ) mcnn annua l powfr i n s e a x l c n g t h of 2GW s t a t i o n

4 . Cap tu re Factor**

mean annua l poucr cap tu red 11y d e v i c e ( X ) rncan annual powcr i n s e a x d e v i c e l e n g t h

F . !elated t o c o s t

1. Cost of 2CW s t a t i o n (unciiscouilted) (01)

2 . Cost o f e a c i ~ d e v i c e ( i lndiscoi~ntc t ! ) (LP[)

3 . Cost of cl\erp,y ( d i s c o u n t e d ) (p/Kwh)

C . ? ~ i s c e l l a n r o u s

1. Hean anr:ual power cha in e f f i c i e n c y ( X ) " " *

2 . A v a i l a b i l i t y of chc 2CW scheme ( X )

3 .

4 .

fi i l iclrlding avili l a b i l i t y f a c t o r

*;? no t i nc lud in l : a v n i l n h i l i t y f a c t o r

h** 111ea1i i~r inual 1~uwcr-la11ded a t Skye ( n o t i n c l u d i n g a v a i l e b i l i t y f a c t o r ) mcnn aniiudl power cap tu red p e r d c v i c e X No. of d e v i c e s i.n schenle

5 ( i i i ) e NEL FLOATING TERMINATOR

1. GENERAL

1.1 DESIGN

The s t r u c t u r a l c a l c u l a t i o n s f o r t h e d e v i c e a r e based on t h e

methods developed f o r t h e d e s i g n of t h e A t t e n u a t o r and a r e i n

accordance w i t h t h e NEL OWC Note 30 and t o a p p r o p r i a t e d e s i g n

c r i t e r i a . The d e v i c e team's d e s i g n phi losophy i s f u l l y

a c c e p t a b l e t o t h e C o n s u l t a n t s .

The Team h a s r e c o g n i s e d t h a t t h e d e v i c e l e n g t h o f 263m w i l l

c a l l f o r a thorough check on t o r s i o n a l load ing d u r i n g

i n s t a l l a t i o n and o p e r a t i o n . T h i s work i s b e i n g under taken

w i t h f u l l l i a i s o n w i t h t h e C o n s u l t a n t s and i t i s n o t

a n t i c i p a t e d t h a t any m o d i f i c a t i o n s t h a t may be found n e c e s s a r y

t o i n c r e a s e t h e t o r s i o n a l r i g i d i t y w i l l have a s i g n i f i c a n t

e f f e c t on c o n s t r u c t i o n c o s t s .

I t i s apparen t t h a t t h e mooring sys tem i s v e r y much a p a r t o f

t h e o v e r a l l d e s i g n bo th a s r e g a r d s s t a t i c and dynamic l o a d i n g

on t h e device/mooring i n t e r f a c e . The C o n s u l t a n t s a r e i n

c o n t a c t w i t h t h e f u r t h e r d e s i g n work b e i n g under taken by SBM

and a r e aware o f i t s p o s s i b l e i m p l i c a t i o n s on t h e s t r ~ i c t u r a l

d e s i g n of t h e d e v i c e . Again i t i s n o t expec ted t h a t any

n e c e s s a r y m o d i f i c a t i o n s w i l l have a s i g n i f i c a n t c o s t p e n a l t y .

1.2 TANK TESTING

The d e v i c e h a s been t e s t e d f o r t h e 46 s p e c t r a and t h e s e t e s t s

t o g e t h e r w i t h p a r a l l e l a n a l y s e s under taken by NEL i n d i c a t e

t h a t t h e d e v i c e h a s a hydrodynamic e f f i c i e n c y o f 25%. T h i s i s

low i n comparison w i t h o t h e r d e v i c e s b u t , a s d i s c u s s e d l a t e r ,

i s compensated by t h e o v e r a l l c a p t u r e p o t e n t i a l a t l O O m d e p t h

and t h e h i g h e r number o f c e l l s t h a t can be i n c o r p o r a t e d i n one

module (12 no. c e l l s ) r e s u l t i n g i n an o v e r a l l need f o r on ly 185

d e v i c e s a s compared t o 589 d e v i c e s i n t h e c a s e o f t h e Raised

Breakwater , b o t h f o r a nominal 2 GW s t a t i o n . T e c h n i c a l

Advisory Group 2 have r e c e n t l y recommended a r e d u c t i o n i n t h e

t h e power a v a i l a b l e a t 100m dep th which h a s been i n c o r p o r a t e d

i n t o the d e v i c e assessment b u t not t h e d e v i c e o p t i m i s a t i o n .

L . .3 S P E C 1 FICA'CION

I n f o r m a t i o n t o d a t e i s b r o a d l y based on t h e NEL summary of

Mechanical and E l e c t r i c a l P l a n t Ra t ing and P r o d u c t i v i t y 20th

November, 1981, on the s t r u c t u r a l d e s i g n phi losophy a s used i n

t h e A t t r n u a t o r d e s i g n and on t h e e a r l i e r NEL r e f e r e n c e

d e s i g n s . Close l i a i s o n h a s been mainta ined between t h e Device

Team and t h e C o n s ~ ~ l t a n t s on any developments and major

m o d i f i c a t i o n s .

Due t o on-going work on. t h e d e s i g n and t h e c a p t u r e phi losophy

a s d i s c u s s e d l a t e r , t h e Device T ~ a m h a s n o t y e t produced a

forrnal s p e c i f i c a t i o n .

F u l l co -opera t ion h a s been main ta ined between t h e Device Team

and t h e C o n s u l t a n t s on c o n s t r u c t i o n c o s t s a n d t h e in fo rmat ion

t h a t i s becoming a v a i l a b l e on i n s t a l l a t i o n c o s t s a s t h e

mooring d e s i g n approaches complet ion. Good agreement h a s been

reached on t h e s t r u c t u r a l c o s t i n g and t h e mooring phi losophy.

Owing t o t h e above c o n t i n u i n g m o d i f i c a t i o n s a formal

p r e s e n t a t i o n of c o s t i n g f o r t h e d e v i c e h a s n o t y e t been

provided by the Device Team.

2 . DEVELOPMENT

2.1 GENERAL

rhe F l o a t i n g Termina to r r e p r e s e n t c the most up-to-date of t h e

Osc i l l a t ing Water Column d e v i c e s a s o r i g i n a l l y conce ived ,

namely a moored t e r m i n a t o r s q u a r e t o the s e a . I t i s

immediately e v i d e n t t h a t any c o s t and e n g i n e e r i n g p e n a l t i e s

r e l a t e d t o t h e i n s t a l l a t i o n and up-keep of t h e moorings i s

compensated by t h e long-term average s e a power o b t a i n i n g a t

lOOm dep th ( 5 3 . 5 ~ w / m ) .

2.2 MAN IFOLD I N G

I n J u n e and J u l y o f t h i s y e a r t h e concept o f man i fo ld ing s i x o f

t h e 1 2 c e l l s i n t o o n e AC power u n i t , i . e . two such power u n i t s

p e r 1 2 c e l l d e v i c e , was examined by t h e Device Team. It was

a n t i c i p a t e d t h a t t h e smoothed power i n p u t , t h e s i m p l e r p l a n t

r equ i rement and t h e reduced dev ice - to - shore t r a n s m i s s i o n could

produce u s e f u l economies w i t h a s m a l l c a p t u r e l o s s . The

r e s u l t s o f t ank t e s t i n g d i d n o t s u p p o r t t h i s view and t h e

sys tem d i s c u s s e d i n t h i s n o t e t h e r e f o r e comprises a 1 :l c e l l

t o t u r b i n e l g e n e r a t o r r a t i o . The p o s s i b i l i t y o f man i fo ld ing is

s t i l l b e i n g examined and t h e c u r r e n t Cadnam t e s t s on a r a i s e d

b reakwate r d e v i c e u s e s a manifolded model.

2 . 3 CHANGES TO DEVICE PROFILE

I t i s expected t h a t t h e p r o f i l e of t h e d e v i c e w i l l be

e s s e n t i a l l y i n accordance w i t h drawing No. FT11 r e v i s i o n 1 of

September 1981. The m o d i f i c a t i o n s t o t h i s w i l l be due t o t h e

i n c o r p o r a t i o n of one p l a n t u n i t p e r c e l l b u t i t i s a n t i c i p a t e d

t h a t t h i s w i l l be l o c a t e d i n t h e a r e a p r e s e n t l y occupied by t h e

HP and LP d u c t s w i t h adequa te f a c i l i t i e s b e i n g provided f o r

a c c e s s , maintenance and p a r t replacement .

3 . FEASIBILITY

Although a c c e p t i n g t h a t some m o d i f i c a t i o n s may be n e c e s s a r y

due t o t h e mooring systems and t o mooring load ing on t h e

d e v i c e , t h e C o n s u l t a n t s cons i d e r t h a t t h e F l o a t i n g Terminator

OWC concep t is f e a s i b l e .

E s s e n t i a l l y t h e c o n s t r u c t i o n sequence is based on w e l l

e s t a b l i s h e d methods, a compara t ive ly s m a l l number o f 1 2 c e l l

modules w i l l be r e q u i r e d t h u s e a s i n g any problems a s s o c i a t e d

w i t h o p t i m i s i n g t h e c o n s t r u c t i o n sequence and i n tow-out and

i n s t a l l a t i o n .

The d e v i c e o b v i o u s l y s u f f e r s from t h e problems o f any moored

d e v i c e i n t h i s w a t e r d e p t h , namely maintenance f o r t h e

moorings themselves and a c c e s s f o r maintenance o f t h e p l a n t .

4 . CONCLUSIONS

I n a g r e e i n g wi th t h e Device Team's c o s t i n g and programme

e s t i m a t e s and i n r e c o g n i s i n g t h e proposed c o n s t r u c t i o n o f t h e

module a s b e i n g a r e a s o n a b l e one , i n v o l v i n g no s i g n i f i c a n t

e x t r a p o l a t i o n o f c u r r e n t e n g i n e e r i n g p r a c t i c e s , t h e

C o n s u l t a n t s c o n f i r m t h a t t h e f l o a t i n g t e r m i n a t o r i s a n

a c c e p t a b l e d e v i c e . Both t h e C o n s u l t a n t s and t h e Device Team

acknowledge t h a t f u r t h e r work i s r e q u i r e d on t h e t o r s i o n a l

r i g i d i t y o f t h e s t r u c t u r e and a l s o p o s s i b l e i n t e r a c t i o n wi th

t h e proposed mooring sys tem when f i n a l l y agreed . Both t h e s e

a s p e c t s a r e a c t i v e l y under examina t ion by t h e Device Team wi th

fu1.l i n t e r a c t i o n w i t h t h e C o n s u l t a n t s . I t i s n o t a n t i c i p a t e d

t h a t any f i n a l and n e c e s s a r y m o d i f i c a t i o n s w i l l have

s i g n i f i c a n t c o s t o r i n s t a l l a t i o n t ime p e n a l t i e s .

NEL FLOATING ATTENUATOR

OWC'SPI NE FLOATING - NEL ATTENUATOR

LEADIN(; DEVICE PAPJMt;'I'I:RS p-p.-.-- -

(ILo_caticin - .+ i~ th U i s t )

A . Re l a t ed t ~ l o c a t i o n

1 . Dis L ~ I I C C c1ffs11orc (k:i)

2 . Water dell ti1 (nil

3. Power i n s e a (Kw/m)

U. Rcla t cd t o d e v i c e

1 . O v e r a l l s i z c - Icnp,th (m)

- breadt l i (in)

- v e r t i c a l dinicnsion (m) 16 2 - g r o s s c r o s s s e c t i o n a l a r e a (m ) 320

2 . Weight c': dev ice ( t o n n e s )

3 . \icip,lit a: d e v i c e f i c n g t h (L-onnesln:)

C . Re l a t ed t o 2GIJ s t ; ~ t i o n

1. Number of d e v i c e s

2 . Sp . ic i~ig of devi c c s (-1)

3 . Lcnqrll [of 2Ci.l s t a t i o n (km) ( e x c l . i invig . z aps )

D . Rc in t ed t o ~ ~ r n ~ l u t t i v i t y

1 . Ra t ing of g e n e r a t o r s (Mu) 1 . 8 + 2 x O . l @ ?!w/device

2 . Powcr jn s c : ~ (Kwlrn) j 3 . 5

3. )!em annua l pcwer de l i ve re t1 t o Skye (Nw/dcvicc)* 0 . 322

1 1 . Mean anrlrial o u t p u t of 2GW n(.he~ne ((;U)* 0 . 4 6 5

1:. Relctccl t o structure cronomy and u t i l i z n t i on of r e s o u r c e ------p- -

1. Elcan nnrlunl povcr d e l i v e r c d p e r d c v i c c f l c n ~ t h of dev i ce (Kw/m)*

2 . Mcan ailnun1 powcr d e l i v e r e d p e r d e v i c e d c v i c e s p a c i n g ( K w / m ) *

3 . O v e r a l l convcrs io i l e f f i c i e n c y of sclicme*

mean annua l o u t p u t oE ?GW schcnie --W -- ( X ) mcnn annuill power iii s e a X leii!:th of 2(;1; s t a t i o n

ineiln . . . . -- snnDwcr . - c ; i p t ~ - ~ i by d e v i c e (7 . ) me:iii oniiual powcr i n sczi x d e v i c e l e n g t h

L ~ $ l a t e ~ l t o cost_

1. Cost o f P(;\< s t a t i o n (uniliscouritcrl) ( £ P I )

? Cost of each dc\, ici . ( u n d i s r o r ~ ! ~ t c d ) (£PI)

3 . Cost o f ci1crGy (disr:ouilted) (Ii/Kwh)

* i nc l i i d ing a v a i l a b i l i t y f a c t o r

* nu t i n c l u d i n g a v a i l i i b i l i t y f a c t o r

*"* mean annua l ~ w e r la~iclcd a t Skye -p- ---- ( n o t i n c l u d i n g a v a i l a b i l i t y f a c t o r ) ~ n e ~ ~ n annua l power cap tu red p c r d e v i c e x No. of d e v i c e s i n scheme

w o r n O d m

S . .

0 0 0

(I]

o 03

0

a3

m I-- m a cl

+ v \ o o m a . . . . . r n L n 4 N C I c n c O 0 \ 0 4 m w ~ . - - c - i -

r-4

o c ~ c o a . . . . m m o n c . l m - 4 0 3 c a a - 4 m

m t - m S . .

o a r . Goad o m r n

-i 7-4

NEL FLOATING ATTENUATOR

1 GENERAL

1.1 DESIGN

The s t r u c t u r a l f e a s i b i l i t y o f t h e t h r e e d e v i c e s p r o p o s e d by

NEL was o r i g i n a l l y examined i n t h e c o n t e x t of a d e t a i l e d d e s i g n

of t h e A t t e n u a t o r , t h i s d e s i g n b e i n g i n a c c o r d a n c e w i t h t h e NEL

OWC Note 30 and t o a p p r o p r i a t e and accep ta* d e s i g n c r i t e r i a ,

The d e s i g n p h i l o s o p h y and t h e c a l c u l a t i o n s a r e f u l l y a c c e p t a b i e

t o t h e C o n s u l t a n t s .

Of t h e t h r e e d e v i c e s , t h e A t t e n u a t o r s u s t a i n s t h e l e a s t o n e r o u s

l o a d i n g b o t h i n i n s t a l l a t i o n and d u r i n g i t s o p e r a t i o n a l l i f e .

F u r t h e r d e s i g n m o d i f i c a t i o n s may be n e c e s s a r y when t h e moor ing

s y s t e m h a s b e e n f i n a l l y d e c i d e d though t h i s is n o t e x p e c t e d t o

g i v e r i se t o any m o d i f i c a t i o n s t o t h e s t r u c t u r e t h a t would

s i g n i f i c a n t l y e f f e c t c o n s t ~ u c t i o n c o s t s .

1 . 2 TANK TESTING

D u e t o e a r l i e r t es t s i n d i c a t i n g i n h e r e n t l i m i t a t i o n s i n c a p t u r e

p o t e n t i a l , o n l y p r e l i m i n a r y t a n k t e s t s have b e e n c a r r i e d o u t on

t h e A t t e n u a t o r . B e a r i n g i n mind t h a t t h e d e v i c e c o m p r i s e s one

f r o n t column w i t h a hydrodynamic e f f i c i e n c y o f 41% and two s i d e

columns o f o n l y 4.6% it is a p p a r e n t t h a t t h e pe r fo rmance o f t h e

A t t e n u a t o r mus t compare un favourab ly w i t h t h e o t h e r d e v i c e s

where e a c h c e l l is f u l l y u t i l i s e d . F o r t h e above r e a s o n s t h e

A t t e n u a t o r h a s b e e n t e s t e d i n t h e N E L t a n k f o r PM c o n d i t i o n s b u t

n o t f o r t h e 46 d e s i g n a t e d s p e c t r a .

1 . 3 SPECIFICAT I O N

T h i s is b r o a d l y b a s e d on t h e NEL summary o f Mechan ica l and

E l e c t r i c a l P l a n t R a t i n g and P r o d u c t i v i t y 20 November 1981 .

C l o s e l i a i s o n h a s b e e n m a i n t a i n e d be tween t h e D e v i c e Team and

C o n s u l t a n t s on s u c h d e v e l o p m e n t s and m o d i f i c a t i o n s t h a t have

b e e n c a r r i e d o u t , t hough e s s e n t i a l l y t h e d e s i g n was f r o z e n

i n J u l y 1981 .

The D e v i c e Team are n o t i n a p o s i t i o n t o p roduce a f o r m a l

s p e c i f i c a t i o n b e f o r e moor ing d e t a i l s have b e e n f i n a l i s e d .

1 . 4 COSTING

F u l l c o - o p e r a t i o n h a s b e e n m a i n t a i n e d be tween t h e Dev ice Team

and t h e C o n s u l t a n t s on c o n s t r u c t i o n c o s t s and close ag reemen t

h a s b e e n r e a c h e d on t h i s . An a s s e s s m e n t o f i n s t a l l a t i o n c o s t s

h a s t o a w a i t c o m p l e t i o n o f moor ing d e s i g n .

2 DEVELOPMENT

2 .l GENERAL

The A t t e n u a t o r forms a v a r i a t i o n on t h e o r i g i n a l NEL theme

of a f l o a t i n g d e v i c e o r i g i n a l l y c o n c e i v e d a s b e i n g normal

t o t h e wave f r o n t . It was a p p a r e n t t h a t , a s i n o t h e r d e v i c e s ,

some advankage c o u l d b e g a i n e d by c a p t u r i n g t h e waves on a

l o n g i t u d i n a l b a s i s and , by s u i t a b l e s p a c i n g o f t h e d e v i c e s ,

b e i n g a b l e t o e x t r a c t t h e same amount o f e n e r g y f rom a p a s s i n g

wave a s t h a t a b s t r a c t e d by t h e T e r m i n a t o r d e v i c e from a r e f l e c t e d

wave. The Dev ice Team c o n s i d e r e d d e v i c e l e n g t h s of lOOm - 200m

and f i n a l l y d e c i d e d upon t h e lOOm a s b e i n g t h e m o s t economic

a s r e g a r d s c o n s t r u c t i o n , p r e l i m i n a r y t a n k t e s t i n g h a v i n g i n d i c a t e d

t h a t t h e t h r e e c e l l u n i t p r o p o s e d was m a r g i n a l l y less e f f i c i e n t

t h a n a f o u r c e l l u n i t - one f u l l s i z e c e l l i n t h e b o w , one f u l l

s i z e c e l l i n t h e s t e r n and t w o h a l f ce l l s o n t h e A t t e n u a t o r s i d e s .

A f u r t h e r m o d i f i c a t i o n was t h e s h a p i n g o f t h e f o r w a r d c e l l i n t o

t h e c o n v e n t i o n a l b o w s h a p e t h u s making tow-out and emplacement

c o m p a r a t i v e l y e a s y and g e n e r a l s e a - k e e p i n g b e h a v i o u r t o l e r a b l e .

2 - 2 AC GENERAT ION

Between J u l y and September 1981 s o m e a t t e n t i o n w a s d i r e c t e d t o

t h e p o s s i b i l i t y o f AC g e n e r a t i o n u s i n g a x i a l f l o w t u r b i n e s and

synchronous a l t e r n a t o r u n i t s w i t h t h e a s s o c i a t e d advanbage o f

f ewer c a b l e s t o s h o r e a t t h e e x p e n s e o f a m a r g i n a l l y r e d u c e d

o v e r a l l e f f i c i e n c y . T h i s i d e a was abandoned a t t h e same t i m e

a s t h e i d e a o f m a n i f o l d i n g f o r t h e o t h e r two d e v i c e s w a s

d i s c o n t i n u e d , m a i n l y b e c a u s e o f t h e a p p a r e n t f a i l u r e o f

m a n i f o l d i n g .

3 FEASIBILITY

A t 105m w a t e r l i n e l e n g t h t h e d e s i g n is c r e d i b l e and t h e s e a -

k e e p i n g c h a r a c t e r i s t i c s would be e x p e c t e d t o be s a t i s f a c t o r y .

However, due t o t h e low c a p t u r e p o t e n t i a l and hence t o t h e f a c t

t h a t some 1300 modules a r e r e q u i r e d it i s s e e n t h a t on economic

g r o u n d s t h e A t t e n u a t o r d e v i c e c a n n o t be c o n s i d e r e d a f e a s i b l e

one and it c a n n o t compete w i t h t h e NEL F l o a t i n g T e r m i n a t o r o r

R a i s e d B r e a k w a t e r . The e f f i c i e h c y g a p c a n n o t be compensa ted

by hydrodynamic o r o v e r a l l h y d r o m e c h a n i c a l c h a i n improvements

and t h e d e v i c e is e s s e n t i a l l y a p o i n t a b s o r b e r o n l y .

Mooring d e t a i l s a r e n o t f i n a l i s e d b u t it is e x p e c t e d t h a t some

form o f f i x e d p o i n t mooring a t t h e b o w and two t r a i l i n g moor ings

a t l e a s t a t t h e s t e r n w i l l be r e q u i r e d . I f t h e d e v i c e s a r e

t o be p o s i t i o n e d s u f f i c i e n t l y close t o g e t h e r f o r c a p t u r e t o be

o p t i m i s e d , n o t more t h a n loom, t h e n some d i f f i c u l t i e s w i t h t h e

mooring s y s t e m c a n be a n t i c i p a t e d t h o u g h t o no g r e a t e r e x t e n t

t h a n t h a t o b t a i n i n g i n t h e F l o a t i n g T e r m i n a t o r .

4 CONCLUSIONS

Whi le a g r e e i n g w i t h t h e Dev ice Team ' s c o n s t r u c t i o n c o s t i n g and

d e s i g n p h i l o s o p h y t h e C o n s u l t a n t s b e l i e v e t h a t s u f f i c i e n t work

h a s b e e n u n d e r t a k e n o n t h e A t t e n u a t o r d e v i c e t o i n d i c a t e t h a t

it h a s no f u t u r e , i t s o v e r a l l p e r f o r m a n c e c a n n o t be made t o

match t h a t o f t h e F l o a t i n g T e r m i n a t o r and t h e R a i s e d B r e a k w a t e r .

E D I N B U R G H DUCK

EDINBURGH DUCKS

Duct! -.-

SECTION A - A

GGrcERAL L A Y O U T I S p i n e u n ~ k 3 0 ~ - l o n g -- -.

,I

C L E V 4 T i Q N

P b o d y .

1,I:AT)INC Ili.VI(:l~: l'.ZIb'iY!~'i'I:l~S

(Loc:it ion - S~iil t l i [ l i s t ) - -- - .- - .. - ' l : l ~ I ! i ~ l ~ ! ~ ~ H l)l!CK .--

A . R e l a t e d t o l o c a t i o n

1 . U i s t a n c c o f f s h o r o (km)

2 . Idater d e p t h (m?

3. Powcr i n s e a (Kw/m)

l;. R e l a t e d t o c levi re

1 . O v e r a l l s i z e - l e n g ~ h (m)

- b r c a d t h (m)

- v e r t i c a l d in i r i l s i o i~ (m) 2 - g r o s s c r o s s s c c t i o n n l a r e a (m )

2 . Wcil:ht of d e v i ~ : e (tonne:;)

3 . Weigl~r o f J c v i c e f l r n g t l ~ ( t o n n e s l n ~ )

C . _Rc.l_;~vLl:y.:_ZgL s~15.i p n

1 . Numbcr C I F d c v i c c s

2 . Spiicii~l: <lcvic:cs (in)

3 . I.rrly,tli <;I 2GW s t a t i o n (km) ( c x c l . n:ivig. gal,::)

2 . Powcr i n sc:! (Kwlm) 53 .5

3 . Mcnr; annual powcr d e l i v e r e d t o Skye (,blw/devic.c)" (0 . h 2 3

4 . Eie:in anilunl o u t p ~ l t of 2GW scheme (GU)* 0 . 5 9 5

E. nf_Ia ted t o s t r u c t u r e economy i111d i i t i l i z n t i o n of r c s o u r r c

1 . Menn nnriunl powcr < l c l i v e r c d p<, r d e v i c e l e n e t h o f d e v i c e (Kw/m)*

2 . Elenn : ~ n ~ l u ; l l powcr i!eLiverc<l p e r d c v i c c ~ l e v i c e s p a c i n g (K~e!m)*

. Overnl l r:nriver:;ian e f f i c i c n c y of schcme*

l'. Ri.i:ltcli t o c o s t . - -. --- -- - - l . Cor,t n l :C!J s t n r i c n (undi!;courl~ ~ . d ) ( f E l )

2 . Cos t of r.lcl1 dcvic t . ( i i n d i s c o ~ ~ n t c ( ! ) (FM)

3. Cost <;E c,ncr!:y (<! js i :ountcd) (ji!Kw11)

C. P l i s c r l l i i neous .- - l . Near1 nnniial power cll;iin cE1ici.enc.y (X)"""

2 . A v a i l a b i l i t y < I £ t h e %(;id sclleinc ( X )

'3 . 4.

' inc luc i ing a v n i 1 : l b i l i t y f a c t o r

*+ not i l , c l i~ t i inf i . ? \~ :~i la! ) i l i t y I n c t o r

* A * mean annun1 y w c r landed a t Gkyc -. - .- --.-- -----W

(no t i n c l u d i n g a v a i l a b i l i t y f a c t o r ) mean ;in;ui.il powcr cnpttirecl pcLr d c v i c c x Xo. of J e v i c c s i n scheme

EDINBUKGH DlJCK

Gene ra l

I t i s assumed t h a t t h e members o f WESC a r e f a m - l i a r w i t h t h e Duck,

f o l l o w i n g p r e s e n t a t i o n s by t h e Team e a r l i e r i n 1981.

The Duck, a s p r o p o s e d , i s a t t h e e x t r e m e end o f t h e r anga f o r most o f t h e

p a r a m e t e r s used t o measure t h e e f f e c t i v e n e s s o f wave e n e r g y d e v i c e s .

I t h a s ,

- t h e h i g h e s t o u t p u t / m o f s e a

- t h e l o w e s t m o o r i n g f o r c e s

- t h e second l o w e s t mass/kW

- t h e second h i g h e s t swept volume r a t i o

- c o n c e p t u a l l y t h e most c o s t e f f e c t i v e power c h a i n

- t h ~ g r e a t r s t number o f i n t e r l o c k i n g and i n t e r d e p e n d e n t sys t ems

- and i n c o n s e q u e n c e tllr l o w e s t a v a i l a b i l i t y

- a u n i q u e d ~ p e n d e n c ~ o n s u c c e s s f u l mPchanica l e n g i n e e r i n g development

t o a c h i e v e v i a b i l i t y .

T h i s i s r e s u l t s f rom a c o n s c iolis d e c i s i o n by t h e Team t o match t h e complex

randomness o f t h e i n p u t e n e r g y o f t h e s e a by a damping s y s t e m c a p a b l e o f

i n s t a n t a n e o u s i n t e l l i g e n t r e s p o n s e , and t o meet t h e damaging h i g h wave

amp1 i . tudes w i t h a c o n t r o l 1 a b l y compl i a n t s p i n e . Resul t i n g from t h i s

p h i l o s o p h y , power o u t p u t i s maximised and s t r l l c t u r a l and a n c h o r i n g f o r c e s

a r e min imised . The r e s u l t i s a d e s i g n which must be n e a r o p t i m a l i n

w e i g h t and e f f i c i e n c y , and which must b e a s s e s s e d i n terms o f t h e

p r o b a b i l i t y o f s u c c e s s o r f a i l u r e a t t h e end o f a s i g n i f i c a n t deve lopment

phase .

Assessment of t h e Concept

Primary I n t e r a c t i n g Sur face

This i s probably t h e most e f f i c i e n t i n t h e wave energy programme. The

wedge a c t i o n allows a high swept volume and t h e n a t u r a l movement of t h e

sea i s wel l matched. The f a c i l i t y t o f l i p over i n a high s e a i s a va luab le

means of l i m i t i n g forces i n h igh seas .

Ref erence Frame

This i s l i kewi se very e f f i c i e n t , i n t h a t f o r most working seas t h e sp ine

can be kept r i g i d ( i f r equ i r ed ) t o maximise output . I n s ea s where t h e r e

i s an excess of energy the s p i n e is a b l e t o "break" a t hinge po in t s t o

l i m i t f o r c e s , both on the sp ine s t r u c t u r e and on t h e moorings. Use of

gyroscopes t o r e s i s t r o t a t i o n makes t h e whole device concept poss ib le .

Power Of f t a k e

High p re s su re hyd rau l i c s us ing a m u l t i p l i c i t y of pumps on cam r i n g s

confers a high volumetr ic e f f i c i e n c y which leads t o low i n s t a l led swept

volume and r e l a t i v e l y low machinery cos t . It a l s o makes p o s s i b l e t h e

system of energy in te rchange wi th t h e two f l y wheels, which i n t u r n allows

t h e power smoothing over many wave cyc l e s , and synchronous genera t ion .

The gyros a l s o provide a l a r g e r e s e r v e of s t o r e d energy, t he b e n e f i t of

which has not been costed.

Given t h e engineer ing means of r e a l i s i n g i t , t h e concept i s hard t o f a u l t .

A s S es sment of t h e Engineer ing

The dev ice i s engineered round t h e concept o f "sealed for l i f e " power

c a n i s t e r s i n each of which 256 r i n g cam pumps, 5 swash p l a t e motors, and

two gyroscopes work cont inuously without maintenance f o r up t o 25 years .

Pumps and motors a r e over provided t o g i v e some redundancy t o a l low f o r

breakdown, bu t e s s e n t i a l l y t h e engineer ing s t ands o r f a l l s on t h e

f e a s i b i l i t y of ach iev ing a very c o n s i s t e n t maintenance f r e e l i f e a s

i nd i ca t ed . Experts consul ted (Mr. Baggett of Commercial Hydraul ics Ltd.

t h e Nat ional Centre of Tribology a t Rise ly and o t h e r s ) a r e no t prepared t o

discount t h e p o s s i b i l i t y t h a t t h i s may be achieved i f t h e necessary e f f o r t

i s made a v a i l a b l e .

An at tempt t o draw comparisons between t h e requi red l i f e of components of

t h e Duck power t r a i n and s i m i l a r components i n presen t day s e r v i c e a r e

presented i n F igs . A and B.

The Duck flywheel bear ings r o t a t e i n excess of 1 0 l 0 r evo lu t ions over a 25

year per iod which is g r e a t e r by 1 o r 2 o rde r s of magnitude than most

r o t a t i n g machinery; b u t i t i s equal led by t h e bear ings i n l a r g e turbo-

a l t e r n a t e r s e t s (660 MW), and by ind iv idua l r o l l e r s i n c r i t i c a l r o l l e r

bear ings i n equipment a s d i v e r s e a s t h e Ro l l s Royce RB 211 engine and i n

t h e main t r a c t i o n a x l e hubs on t h e London Underground. The bear ing

l i n e a r s u r f a c e t r a v e l on l a rge T/A and hydrose ts exceeds t h a t on t he Duck

and provides some reassurance t h a t t he l i f e expectancy requi red on

bear ings can be a t t a i n e d .

The t o t a l p i s t o n t r a v e l on t h e swash p l a t e motor pump i s considerably i n

excess of t h a t f o r o t h e r equipment such a s i n t e r n a l combustion engines of

a l l s i z e s - but t h e s e have t o cope wi th high temperatures causing

ox ida t ion of t h e o i l , contaminat ion of t h e o i l from products of

combustion, and expose t o unclean a i r and f u e l , and meta l p a r t i c l e s from

wear of bear ings . The long l i f e necessary f o r t h i s c r i t i c a l component and

f o r t h e whole high p re s su re hyd rau l i c system i s t o be achieved by ensuring

complete i n t e g r i t y of c l ean o i l supply i n a d ry low p re s su re environment.

This has t o be proved but t h e unce r t a in ty r e s t s heav i ly on achieving an

accep tab l e l e v e l of r e l i a b i l i t y of t he whole system and hence a l l i t s

component p a r t s . The r e l i a b i l i t y a n a l y s i s by YARD g ives an unfavourable

r e s u l t . Notwithstanding t h a t i t has had t o be based on some d a t a obtained

from non comparable a p p l i c a t i o n s t h e f a c t remains t h a t i t c l e a r l y shows

t h a t an order of magnitude improvement i n r e l i a b i l i t y i s r equ i r ed fo r t h e

dev ice t o approach v i a b i l i t y .

The environmental f a c t o r ( t o be appl ied t o t h e f a i l u r e r a t e s ) chosen by

YARD does not r e f l e c t t h e Team's c la im t o c r e a t e a near p e r f e c t working

environment by enc l o s ing equipment w i th in low p re s su re S e a l ed power

c a n n i s t e r s , and t h e r e may be some immediate g a i n t o be i d e n t i f i e d here . . The Consul tants a s se s s t h a t an i n c r e a s e i n r e l i a b i l i t y of about 50 times

over t h e YARD assumptions i s needed t o meet t he system r e l i a b i l i t y

requ i rements c o n c o m i t a n t w i t h t h e a v a i l a b i l i t y o f 80% used i n t h e d e v i c e

c o s t i n g . Marg ina l ly lower component r e l i a b i l i t y might b e accommodated by

more redundancy and system r e d e s i g n .

However t h e d e s i g n o f t h e power t r a i n a l r e a d y i n c o r p o r a t e s redundancy i n

some components which a r e i n p a r a l l e l " f a i l t o s a f e t y " , and t h i s h a s been

allowed f o r a l r e a d y .

P r o d u c t i v i t y

The Duck h a s on ly been t e s t e d i n P-M s e a s i n a narrow tank and

p r o d u c t i v i t y h a s been a s s e s s e d by assuming l i n e a r i t y o f performance w i t h

r e s p e c t t o combinat ion of i n c i d e n t waves from v a r i o u s d i r e c t i o n s .

One s e t of t e s t s i n t h e wide t ank has g i v e n encouraging r e s u l t s , b u t more

r e s u l t s a r e r e q u i r e d b e f o r e one can be s u r e t h a t t h e Duck w i l l n o t s u f f e r

t h e l o s s o f e f f i c i e n c y exper ienced by o t h e r d e v i c e s i n t h e wide t anks .

Meanwhile t h e C o n s u l t a n t s have based t h e i r p r o d u c t i v i t y assessment on t h e

assumption t h a t t h e r e w i l l be no such d rop i n e f f i c i e n c y .

Conc l u s i o n

The C o n s u l t a n t s a r e c u r r e n t l y c o n c e n t r a t i n g a l l t h e i r e f f o r t s t o o b t a i n

t h e b e s t assessment of t h e chance o f a c h i e v i n g s u c c e s s by say 1995.

The c a s e f o r c o n t i n u i n g work r e s t s on t h e i n h e r e n t l y h i g h e f f i c i e n c y o f

t h e d e v i c e , and i t s i n h e r e n t l y low use of raw m a t e r i a l s . It o f f e r s t h e

most scope t o b e n e f i t from advances i n technology i n t h e f u t u r e .

EDINBURGH DUCK - FLYWHEEL BEARINGS

COMPARED TO EXISTING COMPARABLE COMPONENTS

10" Revo lu t ions B e t w e e n Overhau ls

1

660 M W - T / A S ~ . l?

DUCK X

R B 211 c o [ \ e r bear'lnq. X

I( L T E- Underground t r u ~ n mum axle rol ler bear \ng .

l oM

Hy droset X

R .R . Dart X

Taxi use.

I f

10

16 - 10' m (U L * a, 2 V

a, U 0 rC

L

3 cn

16 . - L (3 0 d]

C 0

d

a,

U\gh cipeod macme d i o s ~ . ] . JC

> 0 t t-

a,

18 cc- L 3 m L c3 a C . - .J

16-

X

LOW s p e d

mw,ne d \ ~ ~ c \ .

c /

~ e c t t c Y' use.

D O ~ P S ~ ; ~ f ri dge X

1 08 l 0'

EDINBURGH DUCK - PISTON TRAVEL COMPARED

W I T H EXISTING COMPARABLE COMPONENTS

Revo lu t i ons Between Overhauls

FIG. B

LANCHESTER CLAM

LANCHESTER CLAM

LOCATION OF SCHEME

OPERATING CYCLE

A . R c l a t c d t o l o c a t i o n

1. D i s t a n c c o f f s h o r e (km)

2 . Va t c r dep th (in)

3. Power i n s e a (Kwlm)

U . Re l a t ed t o d e v i c ?

1. O v e r a l l size - l e n g t h (m)

- b r e a d t h (m)

- v c r t i c a l dinlerlsioll (n~)

- g r o s s c r o s s sectional a r e a ( m L )

2 . Weil:lit of dev i ce ( t o n n e s )

3. Weight of d e v i c e f l e n g t h (toilnes/m)

C. Re l a t ed t o 2(iW s t a t i o n

l . N~imbcr of d c v i c c s

2 . Spacing of d e v i c c s (m)

3 . Lcngilt of :!GW s t a t i o n (km) ( e x c l . navig. gaps)

c . !elated t o p r a d u c t i v i t v

1. Ra t ing of g c n c r a t o r s (MW)

2 . Powcr i n s e a (Kw/m) 51.3

3 . Mean annua l power d e l i v e r e d t o Skye (Elw/dcvice)* 1 .77

4 . Mean n n n u ~ l o u t p u t of 2GW scheme (GW)* 0 . 6 0

l:. Re l a t ed t o s t r u c t u r e eLonowy and u t i l i z a t i o ~ ~ of r e s o u r c e

1. Plean annua l powcr [ i c l i ve red p c r d c v i c r f l eng th of d c v i c c (Kw/m)*

2 . Plcno aniirial powcr d e l i v c r c d pe r t icvice + dcv icc s p a c i n g (Y,w/rn)*

3 . Ovc rn l l r onvc r s io l i r f f i c i c n c y o i schclnc*

mean annua l o u t p u t of ?L:\! sche~nc ( X ) mean annu.11 powcr i n sea x I c n g t l ~ of 2GW s t a t i o r l

'I . Capture Pactor**

iw:all a111iua11)o~~r - r ~ r c ~ l - . . - by d e v i c e (%) !nc,nn annua l powcr i n s c n X d c v i c c lengt l i

F. _Related t o c o s t

1. Cost of 2CW s t a t i o n ( u ~ i d i s c o u n t c d ) ( E E f j

2 . Cost of each d e v i c e (undiscot in tcd) (fM)

3. Cost of cncrgy (d i s coun ted ) (p/Kwh)

G. Mi sce l l aneous

1. Mean annua l power c h a i n e f f i c i e n c y (%l*""

L. h v ; ~ i l a b i l i t y of t h e 2GN scltemc ( X )

* i n c l u d i n g a v a i l a b i l i t y f a c t o r

** no t i n c l u d i n g a v n i l n h i l i t y f a c t o r

*** me3n annua l power landed a t Skye P- -- (no t i n c l u d i n g a v a i l a b i l i t y f a c t o r ) mean annua l power cap tu red p e r d e v i c e x No. oE d e v i c e s i n scheme

5 ( ~ ) LANCHESTER CLAM

General

The Lanches te r Clam developed from t h e e a r l y Duck programme and

was o r i g i n a l l y conceived a s an a t t e m p t t o y i e l d a n e n t i r e l y

c r e d i b l e , s i m p l e d e v i c e i n c o n t r a s t t o t h e complexi ty o f t h e Duck.

A c o n c l u s i o n of t h e e a r l y Duck work i n Loch Ness was t h a t s h o r t

f i n i t e s p i n e s work and t h e Clam a r o s e a s a ' s h o r t ' sp ined s i m p l e

wave maker a c t i n g i n r e v e r s e .

The f i r s t engineered r e f e r e n c e d e s i g n y i e l d e d a c r e d i b l e sys tem

w i t h r i g i d f l a p s on h inges and a r u b b e r membrane be l lows between

t h e f l a p and s p i n e . Cos t ing o f t h i s d e v i c e produced very

encouraging f i g u r e s b u t t h e f l a p and a s s o c i a t e d h inges a t t r a c t e d

bo th c o s t and c r e d i b i l i t y p e n a l t i e s . The p r e s e n t d e s i g n u t i l i s e s

a double faced s o f t rubber bag which removes t h e c o s t problem and

cons i d e r a b l y improves t h e c r e d i b i l i t y .

Th i s d e v i c e h a s been t e s t e d i n t h e wide t ank a t Cadnam and h a s ,

s i m i l a r l y t o t h e LFB, y i e l d e d lower p r o d u c t i v i t y than expected.

The e f f i c i e n c y o f t h e Clam is s i g n i f i c a n t l y h i g h e r t h a n t h e LFB.

Th is i s p a r t l y exp la ined by mani fo ld ing l o s s e s i n t h e LFB. The

d e v i c e h a s , however, had on ly one t e s t i n g p e r i o d i n t h e wide t a n k

w i t h a model t h a t i s n o t t r u l y r e p r e s e n t a t i v e o f t h e r e f e r e n c e

d e s i g n . A l / l o t h s c a l e working model i s a t p r e s e n t i n Loch Ness

and r e s u l t s w i l l soon be a v a i l a b l e . T h i s should p r o v i d e some

u s e f u l c o n f i r m a t i o n o f what must be regarded a s c r u d e power

measurements a t Cadnam where a i r power from a s i n g l e c e l l o f l e s s 6 t h a n ' A 3 ' s i z e is measured and s c a l e d by a f a c t o r o f 1 0 .

S t a t u s o f Assessment Data

The b a s i c d e s i g n and c o n s t r u c t i o n a l d e t a i l i n g o f t h e s p i n e a r e a t a

f a i r l y advanced s t a g e and t h e Device Team h a s provided i n f o r m a t i o n

on q u a n t i t i e s which h a s been checked and used a s a b a s i s f o r t h e

C o n s u l t a n t s ' c o s t e s t i m a t e . The Device Team h a s a l s o provided

f u l l d e t a i l s o f t h e i r own e s t i m a t e which i n t o t a l i s w i t h i n

approx imate ly 5% of t h e C o n s u l t a n t s ' e s t i m a t e . A t p r e s e n t a f o u r

cons t ruc t ion f a c i l i t y system is used f o r cos t i ng purposes. The

Device Team i s working on opt imis ing t h e cons t ruc t ion c o s t s by

us ing only two f a c i l i t i e s .

Main and a u x i l i a r y p l a n t c o s t s have been provided by t h e Device

Team and have been accepted p rov i s iona l ly by t h e Consul tants u n t i l

f u r t h e r information from t h e Working Par ty i s a v a i l a b l e .

Transmission c o s t s have been provided based on t h e Consul tants

c u r r e n t working Paper. This working Paper is about t o be rev ised

s i g n i f i c a n t l y and t h e t ransmiss ion c o s t s have been modified t o

take account of t h e s e major r ev i s ions .

I n s t a l l a t i o n c o s t s have been developed by t h e Consul tants f o r t h e

deadweight anchor system proposed by t h e Team. Costing of t h e

mooring components i s t h e Device Teams cos t i ng and has no t been

v e r i f i e d . The o v e r a l l mooring c o s t s inc lud ing i n s t a l l a t i o n f o r

t h e Clam a r e about 25% of t h a t taken f o r t h e LFB. This r educ t ion

i s t o t a l l y a r e s u l t of lower a b s o l u t e mooring loads. The v a l i d i t y

of lower peak mooring loads f o r t h e Clam has no t y e t been

e s t ab l i shed .

Maintenance c o s t s have been assessed by t h e Consul tants and

c o r r e l a t e reasonably w i th t h e Easams Study. A v a i l a b i l i t y has been

der ived from t h e f a i l u r e r a t e s tudy c a r r i e d ou t by YARD.

Development

The des ign philosophy adopted by Lanchester has been t o minimise

t h e r e f e r ence frame c o s t . This they have succeeded i n doing.

Although t h e method of a r r i v i n g a t des ign moments is t o t a l l y

d i f f e r e n t from t h a t adopted by WPL they a r e i n agreement over t h e

magnitude of t h e s e fo rces . By u t i l i s i n g t h e a l lowable s t r e s s e s i n

t h e sp ine t o t h e l i m i t and by avoiding the need t o widen t h e

s t r u c t u r e f o r r o l l s t a b i l i t y , t h e sp ine , a l though 7% longer i s i n

f a c t over 30% l i g h t e r than t h e LFB.

It i s i n t e r e s t i n g t o no t e t h a t a l though conceived a s a pure

te rmina tor , power was opt imised i n t h e wide tank by o r i e n t a t i n g

t h e device 55' from t h e predominant wave d i r e c t i o n . The des i r ed

o r i e n t a t i o n i s a s a r e s u l t w i th in about 15' of t h a t f o r t h e double

s ided ' a t t e n u a t o r ' LFB.

F e a s i b i l i t y

A s mentioned f o r t h e LFB, a rubber membrane i s a very c o s t

e f f e c t i v e system. It has n o t , so f a r , been p o s s i b l e t o develop t h e

shape of t h e Clam bags t o t h e ex t en t t o which t h e LFB bags have

been developed, bu t work on t h e l a t t e r a s regards manufacture,

des ign and handl ing a l l c o n t r i b u t e t o confidence i n t h e Clam bag.

This does have a more complex shape and w i l l t h e r e f o r e r e q u i r e

e x t r a development p a r t i c u l a r l y i n t h e region of t h e duct

connect ions. The bag cords a r e always i n t ens ion whi le t h e

i n t e r n a l a i r p r e s su re i s above atmospheric ( ~ e a n i n f l a t i o n

p re s su re 1.5 atmospheres). This t ens ion permits t h e bag t o t ake a

s i g n i f i c a n t shear load be fo re t h e cords a r e put i n t o compression.

This shea r capac i ty appears g r e a t e r than t h e l a t e r a l wave loading.

It i s however c o n d i t i o n a l on i n t e r n a l p r e s s u r i s a t i o n .

The r e f e r ence frame has been developed i n s u f f i c i e n t d e t a i l t o

permit r e a l i s t i c c o s t and des ign capac i ty e s t ima te s t o be made. A s

mentioned prev ious ly , t h e sp ine is f u l l y s t r e s s e d under extreme

environmental loadings. No weight reduc t ions a r e t h e r e f o r e

conceivable .

The mooring system adopted must be considered a s near t h e lower

bound wi th regard t o c o s t , and inc ludes a number of f e a t u r e s which

a r e a t p r e sen t unproven:-

i ) S u f f i c i e n t compliance i s provided by t h e lead ing l o o T buoy

t o prevent maximum des ign loads being exceeded.

i i ) A Doris type 'Deadweight Anchor' would be a v a i l a b l e o f

s u f f i c i e n t s i z e and shape t o hold when dropped onto t h e

s eabed .

i i i ) Po lyes t e r p a r a f i l rodes , t e rmina t ions and j o i n t s assumed t o

have 25 year l i f e .

Although t h e Clam r e q u i r e s t en i nd iv idua l power u n i t s u t i l i s i n g

s i n g l e s t a g e Wells t u r b i n e s , each u n i t con ta in s only t h e s i n g l e

r o t a t i n g s h a f t . The power u n i t s a r e t h e r e f o r e s imple and should be

r e l i a b l e . Cycl ic e f f i c i e n c i e s a r e reasonably high.

Conc lu s ions

P roduc t iv i t y t e s t i n g of t h i s dev ice i n mixed spread seas i s very

l imi ted and t h e r e may be cons ide rab l e scope f o r improvement. The

p roduc t iv i t y assumed f o r t h i s dev ice however i s a cons ide rab l e

mod i f i ca t i on of t he raw t e s t d a t a measured a t Cadnam and al though

t h e adopted f i g u r e i s agreed, p a r t must be considered a s

specu la t i ve . The Loch Ness t e s t i n g a t l / l o t h s c a l e and t h e

r e t e s t i n g a t Cadnam i n March should permit g r e a t e r confidence i n

t h e assumed va lues and may even demonstrate g r e a t e r p roduc t iv i t y .

6 . WHERE THE MONEY HAS GONE

7. WHAT IS THE AVAILABLE RESOURCE

AT SOUTH UIST ? -

WHAT I S 'THE AVAILAULLl RLSOUKCL A'l' SOU'l'11 ULS'P?

Real s e a s comprise a m u l t i t u d e o f component waves o f v a r i o u s h e i g h t s and

p e r i o d s p r o p a g a t i n g i n a l l d i r e c t i o n s of t h e compass. The power i n t h e

s e a i s c a l c u l a t e d u s i n g wave r e c o r d s from buoys, t h r e e of which have

been deployed by IOS o f f South U i s t t o c o l l e c t d a t a f o r t h e Wave Energy

Programme. However, t h e s e buoys can on ly g i v e i n f o r m a t i o n about t h e

o v e r a l l v e r t i c a l d i sp lacement of t h e wa te r s u r f a c e and n o t t h e

d i r e c t i o n i n which p a r t i c u l a r wave t r a i n s a r e t r a v e l l i n g . Thus a f t e r

F o u r i e r a n a l y s i s of t h e raw d a t a i t i s p o s s i b l e t o c a l c u l a t e o n l y t h e

t o t a l power i n a g iven s e a s t a t e . Conven t iona l ly t h i s i s expressed a s a

power d e n s i t y i n k i l o w a t t s p e r m e t r e , which i s most u s e f u l l y v i s u a l i s e d

a s t h e r a t e a t which energy c r o s s e s a c y l i n d e r of one m e t r e d i a m e t e r ,

s t r e t c h i n g v e r t i c a l l y from t h e seabed t o t h e w a t e r s u r f a c e . It i s t h i s

f i g u r e which i s a t p r e s e n t t a k e n t o be t h e a v a i l a b l e r e s o u r c e .

I n f a c t t h i s i s a f a l l a c y . The power e x p r e s s e d i n t h i s way i s a v a i l a b l e

on ly t o a s i n g l e , i s o l a t e d p o i n t a b s o r b e r . Such a d e v i c e i s p e r f e c t l y

symmetr ica l and responds t o a l l waves i n a s i m i l a r manner r e g a r d l e s s of

t h e i r d i r e c t i o n o f approach. Thus i t can c a p t u r e an e q u a l amount o f

ene rgy from a g i v e n wave t r a i n independen t ly of t h e d i r e c t i o n of

i n c i d e n c e of t h e wave t r a i n . The behav iour o f p o i n t a b s o r b e r s i s r e a l l y

o n l y an e x t e n s i o n of t h a t o f t h e wave measur ing buoys, r a t h e r than

merely measur ing power t h e a b s o r b e r i s a b l e t o c a p t u r e some o f i t .

Thus, i n an i s o l a t e d s i t u a t i o n , remote from any o t h e r mechanisms f o r

removing energy from t h e s e a , a s o l i t a r y p o i n t a b s o r b e r i s exposed t o

t h e whole power which i s ' s e e n ' by t h e buoy, t h e s o - c a l l e d a v a i l a b l e

r e s o u r c e .

More commonly, wave energy d e v i c e s t a k e t h e form o f a t e r m i n a t o r . These

may be s i t e d i n t h e same a r e a a s t h e p o i n t a b s o r b e r , b u t by t h e n a t u r e

o f t h e d e v i c e t h e energy a v a i l a b l e t o be c a p t u r e d i s l e s s t h a n t h a t a t a

s o l i t a r y r e c o r d i n g buoy. For example c o n s i d e r t h e f o l l o w i n g diagrams

showing u n i d i r e c t i o n a l s e a s approaching a p o i n t a b s o r b e r and a

t e r m i n a t o r .

In the latter diagram, it is seen that the effective resource available

to the terminator is reduced from that available to a buoy by a factor

of cos 8. This is purely a consequence of the reduction in device

length presented to the wave crests because of its oblique attitude. It

is not to be confused with any variation in the energy captured by the

device due to alterations in its capture efficiency due to variations in

the angles of wave incidence.

An alternative way of looking at the reduced resource available to a

terminator is to imagine a multi-directional spectrum resolved into two

orthogonal components, one normal to the device, the other parallel.

An isolated point absorber would be able to capture from both components

but for the terminator,once the parallel component has been captured by

the end cells it no longer exists and is not available to the remaining

cells along the line. This effect is particularly pronounced for an

array of terminators many kilometres long. The energy which may be

captured from waves travelling along the line of the array is

negligible. This argument applies to any linear array of devices, not

just to terminators. The array acts as a very long attenuator in which

only the end few devices capture any appreciable energy from wave trains

travelling parallel to the array. It has been suggested that

diffraction will take place to transfer energy along wave crests and

replenish that which is extracted. However, from evidence of

diffraction around breakwaters it seems unlikely to be of significant

consequence.

It should be realised that due to space limitations it is not possible

to study the behaviour of long arrays of devices by wide tank testing.

Therefore care is needed in the assessment of results from single or

small groups of models. One of the limitations of the wide tanks

presently used for testing at Cadnam and Edinburgh is that they can

produce waves only from an arc of approximately - + 75' about a central

direction for a device central in the tank.

waves Generated within this anz

-- I M o d e l - --

I

In the RPT estimation of the productivity of arrays of devices off the

Hebrides this limitation has been regarded as removing from the sea

those components which contribute to the available resource as measured

by buoys, but are not effectively available to the devices. This is an

approximation which the Consultants believe to be reasonable within the

current state of knowledge. However, some Teams disagree with this

approach.

The above has implicitly assumed that devices will be sited in one

straight line array. However, in practice a wave energy station would

require a number of arrays which would be deployed to suit sea bed

conditions. They would change course to follow contours and avoid

unsuitable underwater topography. It is clear that arrays and devices

will interfere with each other's resource, some devices shielding

certain directional components from others.

Typical device,

In the above sketch arrays ( A ) and (C) will shield devices in array (B)

and reduce the resource available to (B). Thus model tests based on the

appreciated that spectral data used for model testing and assessment of

productivity, whilst being a significant advance from monochromatic and

Pierson-Moskowitz seas, is far from perfect and can only be used to give

comparisons and approximate estimates.

As has already been stated, devices have been proposed which would be

sited in depths different from 42m. Estimates for the resource at these

sites have been made by interpolation between data available for water

depths of 15m, 25m and 100m. Long term mean power levels have been

predicted by IOS for these depths by comparing spectra recorded

simultaneously by buoys at these locations and the buoy at 42m.

Buoy Depth Long term mean

(m) power density (kw/m)

Deep water 100 59.2

Offshore 4 2 47.8

Inshore 3 2 5 36.2

Inshore 1 15 15.3

Values are related to the reference power density of 47.8 kw/m at 42m,

but measured data is such that the proportions can be expressed with

confidence. Thus it may be thought at first sight that the available

resource is reducing in shallower water depths. Several mechanisms

have been suggested to explain the reducing values, but there is no

complete, satisfactory explanation. Power can be lost in a number of

ways, eg. turbulence from waves breaking or friction applied by bed

roughness and submarine growth. Such means are necessary to explain the

rapid decay of power in depths shallower than 25m, but work by HRS using

a refraction model suggests that no power is lost in water deeper than

this. The apparent reduction in power density is merely due to dilution

as wave crests are turned and lengthened.

Shore

Orfhogonal --- P&-allel covlburs

No energy c r o s s e s t h e o r t h o g o n a l s and hence t h e d e n s i t y r educes a s t h e

c r e s t l e n g t h s i n c r e a s e . The energy d e n s i t y i s what i s measured by a

buoy. The energy f l u x normal t o t h e c o n t o u r s i s unchanged. It should

be no ted t h a t t h e d imension between two o r t h o g o n a l s measured p a r a l l e l

t o t h e c o n t o u r s i s c o n s t a n t . Thus t h e l e n g t h o f c o a s t l i n e occupied by a

wave does no t p r o g r e s s i v e l y i n c r e a s e a s i t moves i n s h o r e , a common

m i s i n t e r p r e t a t i o n o f t h e above diagram and one which would c l e a r l y be

i m p o s s i b l e .

The HRS r e f r a c t i o n model i n c o r p o r a t e s t h e c h a r t e d s e a bed c o n t o u r s o f f

t h e Hebr ides . The i r r e g u l a r i t y of t h e s e c o n t o u r s i s such t h a t t h e

p a t t e r n o f r e f r a c t i o n of waves i s v e r y complex and n o t e a s y t o v i s u a l i s e

a s i n t h e above i d e a l i s e d s k e t c h . R e f r a c t i o n c a u s e s power d e n s i t y t o be

l o c a l l y c o n c e n t r a t e d and s p r e a d . T h e r e f o r e t h e d i s t r i b u t i o n of power

d e n s i t y o f f South U i s t v a r i e s a long contours. a s w e l l a s w i t h d e p t h .

E s t i m a t e s a t f i v e d i f f e r e n t l o c a t i o n s on t h e 25m c o n t o u r u s i n g t h e model

range from 27.7 kW/m t o 37.3 kW/m w i t h a mean of 30.6 kW/m. Thus

a c c o r d i n g t o HRS i t a p p e a r s t h a t t h e v a l u e o f 36.2 kW/m p r e d i c t e d from

I n s h o r e buoy 3 cou ld be a n o v e r e s t i m a t e o f t h e mean power d e n s i t y

a v a i l a b l e on t h a t c o n t o u r . F u r t h e r work i s n e c e s s a r y . M o d i f i c a t i o n of

s p e c t r a by r e f r a c t i o n o v e r p a r a l l e l c o n t o u r s runn ing nor th - sou th a long

t h e Hebr idean c o a s t w i l l y i e l d a more t y p i c a l mean power d e n s i t y

d i s t r i b u t i o n f o r a long l e n g t h o f c o a s t l i n e , which would be r e q u i r e d f o r

an a r r a y o f wave energy d e v i c e s . T h i s i s y e t a n o t h e r i l l u s t r a t i o n of

t h e u n c e r t a i n t y a s s o c i a t e d w i t h t h e a v a i l a b l e r e s o u r c e o f f South U i s t .

R e f r a c t i o n i s b e l i e v e d t o p l a y a major r o l e i n modifying t h e waves from

t h e Of f shore t o t h e Inshore-3 buoy. However, HRS do n o t r e g a r d i t a s

b e i n g a s i g n i f i c a n t e f f e c t i n d e e p e r w a t e r . Thus f u r t h e r mechanisms

have t o be sought f o r t h e a p p a r e n t l y enhanced r e s o u r c e a t 100m. The

s i t e l i e s approx imate ly 30 km o f f s h o r e and hence h a s a g r e a t e r f e t c h

a v a i l a b l e t o t h e e a s t t h a n t h e o t h e r buoy s i t e s f o r s e a s t o be g e n e r a t e d

by winds blowing o f f s h o r e . Also i t i s i n a more exposed l o c a t i o n and

t h e r e f o r e could be i n a p o s i t i o n t o be a f f e c t e d by waves from around t h e

n o r t h c o a s t of S c o t l a n d which would be s h i e l d e d from t h e o t h e r buoy

s i t e s by t h e Monach I s l a n d s and North U i s t . S a l t e r h a s pu t forward a

t h e o r y t h a t r e l a t i v e l y s m a l l , r e g u l a r u n d u l a t i o n s i n t h e sandy bed a t

t h i s d e p t h a r e r e s p o n s i b l e f o r s e l e c t i v e l y a t t e n u a t i n g c e r t a i n wave

f r e q u e n c i e s . However, t h e answer i s a s y e t unknown,

For the present, with no further data for tank testing and productivity

assessment, RPT have set out a linear transformation for the IOS spectra

determined for 42m depth to produce an available wave climate for

devices at other depths. This is based on the long term power density

predicted for all the buoy sites. The transformation applies to water

depths deeper than 30m for which depths it has had to be assumed that

the directionality remains constant. For 25m depth, where the

directional band of wave energy has been narrowed due to refraction,

spectra resulting from the HRS refraction model have been used. Doubts

concerning their representativeness have already been expressed.

In conclusion, the answer to the question posed at the beginning of this

discussion is that after nearly 6 years of recording there are still

many unknowns and it is not possible to state with confidence the mean

power a device will be exposed to during its lifetime. At the site with

the best data (42m depth) the accepted value for long term mean power

density of 47.8 kW/m used as a reference for all sites, is an estimate

and its directional distribution has had to be inferred from wind data.

Even less confidence can be put on data for other sites owing to

refraction, shielding, energy dissipation and perhaps other, as yet

unidentified effects. Tank tests at this stage should be used to

compare devices, not to assess their absolute productivity, but even so

it must be realised that fair comparisons may not be possible without

further understanding of wave behaviour off South Uist. Finally it is

important to realise what is implied in defining the available resource

using a power density only. Due to device shape, interaction and

shielding this is not the power per metre run the devices are exposed

to.