oscillating wind energy conversion system

8/19/2019 Oscillating Wind Energy Conversion System

1/24

SERl/TR 211 1911

UC Category: 60

DE84000087

Oscillating Wind Energy

Conversion Systems

Peter South

Richard Mitchell

December 1983

Prepared under Task No. 1067.10

WPA NO.171 83

Solar Energy Research lnstitute

A

Division of Midwest Research Institute

1617

Cole Boulevard

Golden Colorado 80401

Prepared

for

the

U S Department of Energy

Contract No. DE-AC02-83CH10093


2/24

Printed in the United States of America

Available from:

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

Springfield VA 22161

Price:

Microfiche A01

Printed Copy A02

NOTI E

This report was prepared as an account of work sponsored by the United States

Government. Neither the United States nor the United States Department of Energy

nor any of their employees nor any of their contractors subcontractors or their

employees makes any warranty express or implied or assumes any legal liability

or responsibility for the accuracy completeness or usefulness of any information

apparatus product or process disclosed or represents that its use would not

infringe privately owned rights.


3/24

PREFACE

The i n fo rmat i c rn i n t h i s docriment sui:qcst ; t : je C)sci n :.in;: [. iiigJ E~?el-,zyCon-

v e r s i o n S ys Cm s 6:-I n o t a p p e a r t o have s i ~ r j i f i c n ~ rt lv ;~r . tn re : ;

o v e r

ecl~ii\.-

a l e n t c o n v e n t i o n a l r o t a t i n r - l l e n e n t wind t3nt rgy conver s ion svs t c>ms . I n

f a c t ,

n m o s t c a s e s i t a p p e ar s t h a t t h e y h a ve s c v c r a l d i sa c lv a nt a gt 3 s.

Tnc

doc~:mi?nt

a d d re s s es t h e o s c i l l a t i n g c a b le - t y pe w i n d e n e r g y c o n v e r s i o n s v s t c l r l

i t s

w e l l

a s

t h o s c i l l a t i n g v an e a nd t h e o s c i l l n t i n g wing. I i~dv;lnt ;lgrss and d i s -

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

case

compar i son

i s

made bc t seen i t a n d a c o n v e t l t i or l a l r o t a t i - n g - e l e m e n t w i nd

c n t t r f y

c o l l v e r s i o n

d e v i c e . t a p p e a r s u n l i k e l y t h a t a ny of the: o s c i l l a t i n g e le m e n t c or lc e pt s c a n

c om pe te w i t h t h e p r e s e n t g e n e r a t i o n o f c o n v e n t i o n al w in d e n e r f y s ys te ms .

Approved f o r

S0LP.R

ENERGY

RESE RCH I N S T I T U T E

.

Donald Ritchie, P lana ger

Solar FJectr ic Conversion

Research

Division


4/24

s n TI?-1911

T BLE

O

CONTENTS

aqe

.0 In t roduc t i on 1

.0

Os ci ll at in g- Ca bl e WECS

7

.0

Oscillating-Vane WECS 11

Q Osci lla tin g-Wi ng IJECS 15

5.0 Conclusions 17

6.0 k f e r e n c e s 1 9

LIST

O

FIGURES

-1 Cross Se cti on of

a

Typical O s c i l l a t i n g - A i r fo i l WECS 2

-2 Osc il la ti ng -C ab le WECS 2

-3 Os ci ll at ing- Va ne WECS

3

4

Rigid Wing O sc i l l a t i ng i n a Support ing Track

4

-1 Comparable Skipping-Rope Dar r i eus ) and Osc il l at ing -Cab le WECS 10

-1

Oscillating-Vane

WECS

Rielawa Model)

2

3-2 VAWT Comparable t o th e Osc illa ting -Va ne WECS

12


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SECTION 1 0

INTRODU TION

In te re s t i n os ci l l a t in g- el em en t wind energy convers i on systems (WECS) was

generated when

i t

was s u g g e s t e d t h a t t h e s e s y st e ms c o ul d b e b u i l t w i t h r e l a -

t i v e l y s imple e lements . Because th e main pa r t of th e s t ru c t u r e would be

e x t r a c t i n g e ne r gy f ro m t h e wind , t h e c o s t o f t h a t e n er g y would b e r e l a t i v e l y

low. F igure 1-1 shows a c r os s se c t io n o f a ty p i ca l os c i l l a t in g- a i r f o i l WECS.

Three b a s i c ty pe s of osci l l a t in g- el em en t WECS have been proposed. In t h e

f i r s t t y p e , t h e o s c i l l a t i n g - c a b l e WECS, t h e g a l l o pi n g c h a r a c t e r i s t i c o f

a

s t r e t c h e d c a b l e i s enhanced by va r i ous aerodynamic shapes . The s t r u c t u r e i s

mainly made up of a set of ca b l es s t r e t ch ed be tween two anchor po in t s , and

power

i s

e x t r a c t e d from e i t h e r t h e l a t e r a l o r a x i a l m ot io n o f t h e ca b le s . The

os ci l l a t in g- ca bl e WECS

i s

shown sc he ma ti ca l l y i n Figure 1-2.

The second typ e of osc i l l a t ing -e l eme nt WECS use s an a c t iv e e lement t h a t i s

c a n t i l e v e r e d f r o n a b as e . The a er od yn am ic p r o p e r t i e s of t h i s a c t i v e e l em e nt

a r e c o n t r o l l e d t o p ro du ce t h e a p p r o p r i a t e o s c i l l a t o r y f o r c e s . Thi.s t y p e of

o s c i l l a t i n g WECS, t h e os ci ll at in g- va ne WECS, i s shown schematical ly i n

Figure 1-3.

The t h i r d t y p e o f o s c i l l a t i n g - e l em e n t WECS u s e s a w i ng t h a t moves i n a d i r ec -

t i o n n orma l t o t h e w in d. T h is n o t i o n i s con s t r a in ed by some fo rm of t ra ck ,

and power i s e x t r a c t e d f ro m t h e m o t io n o f t h i s wing. T h i s t y p e , t h e o s c i l -

lating-wing WECS,

i s

shown i n Fi gu re 1-4.

The be ne fi t of a WECS, ene rgy prod uct io n, must be compared wi th t h e co st of

bu i ld ing , in s ta l l i ng , and main t a in ing th e WECS. The e f fe c t iv en es s o f any WECS

depends on

i t s

o v e r a l l b en e f i t - t o -co s t (B/ C) r a t i o . T hu s, t h e m os t i m p o r t an t

p a ram e t er of i n t e r e s t i n ev a l u a t i n g a WECS

i s

t h i s r a t i o .

t

i s u s u a l l y p o s -

s i b l e t o o b t a i n a r e as o na b ly a c c u r a t e power c o e f f i c i e n t (C b a se d o n s we pt

P

a r e a ( t h e s p ac e oc cu pi ed by t h e r o t a t i n g o r o s c i l l a t i n g b l a d e ) , b ut t h i s

p a r a m e t er h a s

l i t t l e

meaning un less

i t

i s d i v i d ed by t h e c o s t p e r u n i t o f t h e

swept ar ea of th e WECS. Hence, comparing wid ely d i f f e r e n t WE S s o l e l y o n t h e

b a s i s o f o b t a i n a b l e power c o e f f i c i e n t s d o e s n o t a c c u r a t e l y compare t h e c o s t o f

t h e en e rg y t h a t t h ey p ro d u ce .

T he power co e f f i c i en t b a s ed on s wept a r ea ca n b e p a r t i cu l a r l y m i s l ead i n g when

i t i s

app l ie d t o dev ices l i k e th e osc i l l a t ing -e l eme nt WECS, where the swep t

a r e a i s p r o p o rt i o n a l t o al lo we d mo ti on a s w e l l a s t o t h e s i z e of t h e s t r u c -

t u re . For ex am pl e, i f i n a g i v en s i t u a t i o n , d o u b l in g t h e amount of t h e e l e -

men t ' s mot ion p roduces

1.5

t i m e s t h e power o b t a i n e d p r e v i o u s l y , t h e p would

only be 75 of what

i t

was befo r e , hu t t he power ou tpu t f rom th e s t ru c t u r e

w oul d i n c r e a se . S i n c e c o s t s p e r t a i n t o t h e s t r u c t u r e a nd n o t t o t h e amount of

motion

i t

a l l ows , i n our example

i t

i s obv ious th a t th e co s t o f energy would

b e r ed u ced by u s i n g a l o wer po wer co e f f i c i e n t .

more p r ac t i ca l parameter i s th e power loa d ing parameter , TAP Power o t~ tpu t

i s d i v i d e d

by

t h e power f l o wi n g i n

a

s t r eam t u b e h av i n g a c r o s s - s e c t i o n a l a r e a


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7/24


8/24


9/24

e q u al t o t h e a r e a of t h e a c t i v e s t r u c t u r a l ~ l c n e n t . : lax imizing the po mr

l o a d i n g p ar a m et e r, t h e n , m ax im iz es t h e p ow er a v a i l a b l e f r m t h e s t r : l c t u r e .

The power loa di ng par am et er , however,

i s

n o t a u sef t 1 1 t oo l. f o r c o ~ ~~ p a r i . n p

wide ly d i f f e r e n t WECS.

rt

fact

i t

could

h e

a rg ut ?d t l l i ~ t h e o n l y r e l e v a n t

p ar am et er of r e a l i n t e r e s t i n e v al . u at i np a

I E S

i s t h e c o s t of h u i l d i n g an d

m a i n t a in i n g o n e f o r a g i v e n e n er gy o u t p ut . % v l o u s l v , i t i s n o t p o s s i b l e t n

e s t i m a t e c o s t s a c c u r a t e l y a t a v e r y e a r l y s t n a e i n t h e clevelopm ent o f

c o n ce p t. R e g a r d l e s s o f how go od a n y p a r t i ci l l . n r p a r m e t e r a p p e a r s t o h e , t h e

concept i s v a l u a b l e o n l y i f : i t produces a B /C r i l t i o b e t t e r t h a n t h a t o f a ny

comparable dev ice . Probab ly th e be s t method

i s

t o co npc ?re t h e d e v i c e w i t h a

comparably des igned con ven t io nal system and t hen a nal yze the wav i n which

t h e i r a s s o c ia t e d c o s t s and b e n e f i t s d i f f e r .

The power c oe f f i c i e n t hased on swept a r ea can be us e fu l a s an in d i ca to r o f

p e rf o rm a nc e a n d c a n b e u se d t o d e t e r m i n e t i l e l ip p er

l i m i t

of th e de v ic e ' s power

o u t p u t . If t h e c a l c u l a t e d p ower c o e f f i c i e n t b a se d o n swe pt a r e a e x c e e d s , o r

e v e n c l o s e l y a p p r o a c he s , 0.59,

i t

i s

a g ood i n d i c a t i o n t h a t e i t h e r t h e c a l-

c u l a t i o n s a r e i d e a l i z e d o r t h e r e h a s b een a n e r r o r .

Tine prima ry power e x t r a c t i o n mecharlism i n

a VECS

c a n h e e i t h e r a e ro dy na ., i

r

l i f t o r ae rodynamic d rag . However, ae rodynan ic d ra g i s a s so c i a t e d w i t h r e 1 . a -

t i v e l y low s p e e d s , l a r g e f o r c e s , a nd l a r g e a c t i v e a r e a s , and i t r e s u l t s i n a

r e l a t i v e l y h i g h e n e rg y c o s t , e x c ep t i n v e r y s p e c i a l i z e d a p p l i c a t i o n s . Hence,

t h e f o l l ow i n g d i s c u s s i o n

i s

c o n ce r n ed p r i na r i 1 . y w i t h d e v i c e s t h a t ris aero-

dynamic l i f t a s the p r imary power ex t ra c t io n nechan i sm.

W it h ae ro d yn a mi c l i f t , p ower i s e x t r a c t e d f r om t h e w in d by m ovinp t h e l i f t i n g

e le m en t a c r o s s t h e w in d. g e n e r a l c h a r a c t e r i s t i c o f l i f t i n g a c ti . ve -e le m en t

WECS

i s

t h a t f o r a g iv e n Cp t h e r e q ui re d s o l i d i t y ( t h e r a t i o of t h e b la de

a r e a t o t h e swep t a r e a ) i s r e l a t e d t o spe ed r a t i o . The h i ~ h e r h e r a t i o of

l i f t i n g e le me nt s p ee d t o wind s p ee d , t h e l o w er t h e r e q u i r e d s o l i d i t y . A t low

s o l i d i t i e s and h i gh sp eed r a t i o s , t h e r e qu i re d s o l i d i t y n i s a p p ro x i ma t el y

i n v e r s el y p r o p o r t io n a l t o t h e s q u a r e o f t h e s pe ed r a t j o f o r a n i d e n t i c a l Cp.

F or a n y . IJECS w i t h l i f t i n p e l e m e n t s , t h e c h o i c e , t h e n , i s b e tw ee n h z vi n g a

r e l a t i v e l y l a r g e a c t i v e a r e a n ov in g a t a low s pe ed o r r e l a t i v e l y s m a ll

a c t i v e a r e a m ov ing a t a h i g h s p ee d , o r a n y co m b in a ti o n o f t h e s e b et we en t h e s e

two extre mes. The ch oi ce i s a f un da me nt al o n e, h c c a ~ ~ s e i g h - s o l i d i t v ,

lo w- sp eed a i r f o i l s a r e s u b j e c t e d t o f a i r l y low p r e s s u r e s a nd c s n be made r e l a -

t i v e l y c r u d e l y frorn l ow- gr ad e m a t e r i a l s ; l o w- sol -i d it v, h ig h- sp ee d a i r f o i l s ,

h ow ev er , r e q u i r e n o r e s o p h i s t i c a t e d d e s i g n , m a n u f a ct t ~ r e , an( m a t e r i a l s u se .

( No te t h a t , wh i l e t h e ae r o d y n a n ic p r e s su r e s N / m L )

a r e

q u i t e d i f f e r e n t , a er o -

dynamic loads K ) a r e s i m i la r .

he c o s t o f c o nv e r si o n t o e l e c t r i c a l power u s u a l l y i n cr e ii s es :>it ? tile naximun

fo rc e o r to rqu e produced by t he p r imary dev ice . On I .arge nac: >iqes , t l ic power

conversion mechanism i s a s i g n i f i c a n t f r a c t i o n of t h e o v e r a l l c a s t of t h e

machine; henc e , power c onver sion co st s tend t c prc?do~nignte and t o ?e na l i ze

h i g h - s o l i d i t y m a c h in e s.


10/24


11/24

SECTION

2 0

OSC ILL TING C BLE WECS

The phenomenon of ca hl e os c i l l a t i o n has been

a ma:jor ? r o \ l e n

f o r u s e r s

o f

t r a ns n i i s s i on l i n e s f o r s om et im e.

t

beco~.rles part icu .arly se ve re when th e

shape of the ca h l e changes because of t he acc re t io n

of

i c e . 'iurnerous in ve st i . -

g a t o r s h av e s t u d i e d t h i s p r o b l e n , h o pi ng t o f i n d some

vay

t o a l l . e v i a t e

t s

a d ve r se e f f e c t s . Althoug h i n v e s t i g a t o r s u nd er st oo d t h a t t h i s o s c i l l a t i o n

n e c e s s i t a t e s a n e x t r a c t i o n o f e ne rg y f ro m t h e w in d, n o s e r i o u s p r o p o s a l s

t c

us e t h e phenomenon a s a p r a c t i c a l w ind ene r gy e x t r a c t i on d e v i c e w e re pu t f o r t h

u n t i l Payne d i d s o i n 1 9 7 7 [ I ] . Payne a l s o s u g g es t ed t h a t v e r y l a r g e , o s c i l -

l a t i n g - c a b l e WECS m ight be f e a s i b l e and a dva nt a geous when na t u r a l t e r r a i n i s

u s ed f o r s u p p o rt .

Other

i n v e s t i g a t o r s may h av e b ee n d e t e r r e d f r om p u r s u i n g c a b l e o s c i l l a t i o n a s

an energy ex t rac t ion mechani sm because

i t

i s

no t ve r y e f f i c i e n t when c oup le d

wi th t he geometry and aerodynamic mechanisms th a t op er a t e i n a na t ur a l

e nv ir on me nt . I n a ny c a s e , t h e i r e f f o r t s w er e aimed a t s u p p r e s s in g t h i s

phenomenon.

n

f a c t , u s in g c a b l e o s c i l l a t i o n a s a n e ne rg y e x t r a c t i o n mech-

a n i s a r e q u i r e s a l oo k i n t h e o p p o s i te d i r e c t i o n , i . e. , e nh an ci ng th e n a t u r a l

phenomenon s o t h a t

i t

becom es a v i a b l e ( more e f f i c i e n t ) enerCqy e x t r a c t i on

mechanism. In a s t ud y funded by SER I [ 2 ] Payne analyzed hot11 cable osci l -

l a t i o n and t h e b i na r y f l u t t e r o f a c a b l e s t r u c t u r e m o di fi ed t o form an

a i r f o i l .

T h at a n a l y s i s o f c a b l e o s c i l l a t i o n s u g g e s t s t h a t r ea s o n a b l e power c o e f f i c i e n t s

b as ed on s wept a r e a a r e o b t a i n ab l e a t r e l a t i v e l y hi g h ca b l e f l u t t e r f r e -

que nc i e s . To s i m p l i f y t h e a n a l y s i s , t h e ve l o c i t i e s t h a t wou1.d be i nduc ed

n or ma l t o t h e wind d i r e c t i o n a r e u s u a l l y i g n o re d .

And

i n f a c t , t h e d ynamic

p r e s s u r e v i r t u a l l y i gno r e s t ha t no r ma l componen t be c a us e o f t he ].ow c a b l e

v e l o c i t y. Hence, t h e a n a l y s i s s t r i c t l y a p p l i e s o n l y when t h e l a t e r a l v e l o c i t v

o f t h e c a b l e i s s m a l l c om pa re d w i t h w ind v e l oc i t y and when th e cab le ' s

d iamete r i s s m a l l com pared w i t h t h e l a t e r a l m o ti on. Along w i t h t he s e qu a l i -

f i c a t i o n s , t h e a n a l y s i s a l s o shows t h a t a s i m pl e c a b l e

WECS

presents some

formidable p r a c t i c a l p robl.er is.

more i n t e r e s t i n g p o s s i b i l i t y t h a t Payne i n v e s t i g a t e d

i s

t he b in a ry f l u t t e r

WECS

i n w hic h

a

d ev ic e t h a t a c t s a s a n a i r f o i l

i s

s t re tc he d between two

c a b l e s . t h a s b e e n s u g ge s te d t h a t a n i n e x p e n si v e m a t e r i a l c o ul d b e s t r e t c h e d

between the t$ iO c a b l e s t o p r ov i de t h e s u r f a c e of t h e a i r f o i l . T his i s

a

q u a s i - st e a d y - st a t e a n a l y s i s i n wh ic h t h e v e l o c i t i e s t h a t a r e i nd uc ed n or ma l t o

t he wind d i r e c t i o n a r e i gno r e d a nd t he a ng l e of p i t c h

i s

assumed t o

h e

sm al l . ' h e a s s m p t i o n s a l s o imply t h a t t h e a i r f o i l v e l o c i t y i s small compared

wi th th e wind ve loc i ty .

The a n a l y s i s a l s o s u g g e s t s t h a t , i d e a l l y , t h e d e v i c e ca n h av e a

Cp

t h n t

reaches the Zanches ter-Betz

l i m i t

However , i n or de r t o ach ieve a h i ,gh pow r

c o e f f i c i e n t , t h e e f f e c t i v e c ho rd ( t h e d i s t a n c e betw ee n thc two cahles ) nus t

g r e a t e r t h a n t h e v e r t i c a l m ot io n an d t h e v e r t i , c al v e l o c i t y

of

t he a i r f o i l

mist

e xc ee d t h e w ind ve l oc i t y . The h i gh vc 1o c i . t ~ nd r e l a t i v e l : , ~ 1 .a rge c ho r d or t h e

a i r f o i . 1 te nd t o v i o l a t e some o f t h e i n it i t 3 1 a s s u m p t i ~ n s

of

t h e a n a l y s i s

nil i


12/24

make th e r e s u l t s somewhat q ~ e s i . onab le ; however, t he r e su l t s i nd i ca t e t ha t

some g e n er a l t r e n d s e x i s t .

As

wi th any o t he r l i f t i ng -e l em en t

WECS

we must

e l t h e r ha ve a h i gh r e l a t i v e s pe ed o r a l a r g e s u r f a c e a r ea .

Because s t re tch ing

th e a i r f o i l between two cab l es makes h igh speeds im poss ib le , a l a rge su r fac e

a r e a

i s

requi red .

Payne s an al ys i s s ugg es t s power outp uts f rom such

a

de vi ce based on a power

coeff ic ien t tha t approaches the Lanches ter -Retz l i m i t . R e a l i s t i c a l l y , t h e

o b t a i n a b l e power w ould p ro ba bl y b e s i g n i f i c a n t l y l e s s , a f t e r v a r i o u s l o s s e s

a r e t aken i n to accoun t .

The power e xt ra ct io n method proposed would emanate from th e re ci pr oc at i ng

a x ia l motion of the ends of the cable . This a x ia l motion could be used t o

pump a working f l u i d throu gh some con ve rs ion mechanism t o produce u sa bl e

power. The i n i t i a l conversion, however, from an enormous fo rc e t r av el in g a

s h o r t d i s ta n c e a t a

l o w

s pe e d p r e s e n t s a s i g n i f i c a n t t e c h n i c a l problem .

For example, i f th e average wind speed normal t o a c a b l e i s 6.7 m / s (15 mph),

a s t r e t c he d cab l e wing 1524 m (5000 f t ) l ong wi th a 152- (500- f t) cho rd t h a t

o p er a te s a t a

p

of 0.4 would produ ce an av er ag e of abo ut 10

W

of power

(as suning t ha t t he dev i ce opera t es e f f i c i e n t l y over a wide range of wind

spe eds ). The i n s t a l l e d power would be about 70

MW

The a i r f o i l would be

cycle d through a 46m (150-f t) range a t midpoin t and would produce an a x i a l

motion of about 3.7 m (12

f

) a t one end of t he cab l e i f t he o the r end were

fixe d, Ass min g a frequency of 0.07 z and two power s t ro ke s pe r cy cle , an

8

average fo rc e of about 13.3 x 10 N would be exerted on the power conversion

mechanisn. To make t h e change i n ca bl e le ng th cause d by power loa ds rel a-

t i ve ly smal l compared wi th th e d i sp lacement , a s t r e s s l ev e l of about 6.9 x 10

7

N/m2 ( 10 ,0 00 p s i ) would b e i n d i c a t e d f o r a s t e e l c a b l e ( t h e o v e r a l l s t r e s s du e

t o pre ten s ion would be much gre ate r ) . Hence, a t o t a l cab le cro ss -s ect iona l

a rea o f

1.9

m2

(3000 in.2) i s i n d i c a t e d f o r a c a b l e m ss of about

22.7

x

lo6 Kg.

The s k i n s t r e t ch ed be tween t h e two cab l es would c a r ry an ave rage p res su re d i f -

fe re nc e of a few newtons pe r squa re meter a t maximum power. For a di st a n c e

between ca bl e s of 152

m

( 50 0 f t ) , a t e n s i l e l o a d o n t h e o r d e r o f 454 kg/m

(1000 l b / f t ) of l eng th would be expected ; t h i s

i s

a cy c l i ca l l oad ing . There

would a l so be load s caused by r a in and snow, and ma te r i a l would be subj ect ed

t o u l t r a v i o l e t r a d i a t i o n . T aking a l l t h e s e f a c t o r 3 i n t o a c e u n t , t h e minimum

5

weight of th e sk i n would probably be about 96 ~ / m 2 l b / f t

.

For a 1524-

(5000-ft ) by 152-m (500-ft ) ar ea , th e t o t a l weight of th e ski n would be about

5 mil l ion pounds.

6If th e wing s t ru ct ur e weighed about 22.7 x 10

Kg,

a s t h e s e r o u h c a l c u l a t i o n s

sug ges t , a dynamic pre ssu re of about 888

N /m 2 (18.5 l b l f t a t a l i f t

c o e f f i c i e n t o f 1.3 would b e r e q u i r e d t o s u pp o r t t h e w ei gh t s t a t i c a l l y .

A

dynamic pr es su re of 888 ~ / m ~18.5 1b/f t 2 ) corresponds t o a wind speed of

about 37.7

m / s

(843 mph). O sc i l la t i on s can occu r a t wind speed s much lower

than t ha t , bu t a s ig n i f i ca n t amount of t ime would be requi r ed fo r the ampli -

t u de t o b u i l d u p t o t h e optimum. I h e g r e a t w e ig ht a l s o i m p l i e s t h a t , u n l e s s

g r e a t c a r e

i s

t ak en t o re du ce i n t e r n a l f r i c t i o n , t h e r e would be l i t t l e n e t

outp ut a t moderate winds .


13/24

T:-

~ l e lbo;re c a l . c u f s t ion w s c a r r i e d o u t f o r a l a r g e - s c a l e s ys te m t o i n c l u d e t h e

a d v an t a ge s t h a t h a ve S e en c la i me d f o r l a r g e s ys t em s .

t

d o e s n o t i mp ly t h a t

a n a i r f o i l s t r e t c he d betwe en two c a b l e s c a n ne ver be e c onom ica l , bu t

t

doe s

sug ges t t h a t t h e well-known squ are cube law becomes burdensome a t a s pan of

1524 5000 f t ) . I f th e span and chord were reduced by

a

fa c t o r of two,

power o ut pu t would be red uced by

a

f a c t o r of f o u r; t h e s t r u c t u r a l w ei gh t,

however, coul.0 he reduced by a f a c t o r of e i g h t i f t h e s t re s s l e v e l s w ere t h e

same. Hence , t h e s t r u c t u r a l we igh t p e r u n i t o f power wou ld he ha lve d.

f

t h e

o s c i l l a t i n g ca hle WECS

i s

t o b e c o m p et i t i v e , t h e n ,

t

would h a ve t o b e a t

s i z e s rnuch sm a l l e r t ha n 100 MW

h i. gh -m od ul us , l o w -d e ns i ty c a b l e m a t e r i a l w i t h l ow i n t e r n a l l o s s e s c o u ld b e

a n a l t e r n a t i v e t o t h e s t e e l c u r r e n t l y pro po sed .

A t

p r e s e n t , t h o u g h , m a t e r i a l s

t h a t h av e p r o p e r t ie s s u p e r i o r t o s t e e l t e nd t o b e e xp en si ve.

The s t r e tc hed -ca ble , o s c i l l a t i n g WECS

i s

a na logous t o t he c o nve n t iona l c ur ve d-

bla de Dar r ieus machine ; a s imple compar ison be tween th es e two n i gh t prove

i n s t r u c t i v e . A t h igh t ip - spe e d r a t i o s , t h e a e rodyna mic pe rf o rm a nc e o f t he two

d e v i c e s s h o u ld be v e r y s i m i l a r a t t h e same ti p - sp e e d r a t i o s an d s o l i d i t y .

A t

t h e same maximum t i p sp eeds and th e same maximum di me ns io ns , t h e maximum

a c c e le r a t io n of th e b la de would a l s o be s i m i l a r i n bo th WECS. The m otion o f

th e Darr ieus- ty pe bECS would be s i m i l a r t o a sk ip pi ng rop e Fig ure 2-1). The

m a jo r d i f f e r e n c e s be tw ee n t h e two d e v i c e s a r e

1)

i n t h e Darr ie us- t ype WECS,

t h e r e

i s

n o need f o r en er gy t o b e s t o r e d t o r e v e r s e t h e d i r e c t i o n of m ot io n o f

t h e wing, and 2 ) power i n t h e D ar ri eu s WECS is p r ov i de d i n t h e f or m o f r o t a r y

m ot ion. Thus, f o r sm a l l kXCS, t he s e two a dva n ta ge s in d i c a te th a t t he Da r r i e us

ty p e WECS would he more t e c h n i c a l l y and econ omic ally v ia bl e. For l a r g e WECS,

t h e p r e vi o u s a n a l y s i s i n d i c a t e s t h a t o s c i l l a t i n g c a b l es would n o t b e

p r a c t i c a l . A t n o s i z e , h owever, d oe s t h e o s c i l l a t i n g c a b l e , g a l l o p i n g o r

bimary f l u t t e r , a p pe ar t o be c o m p e t it i v e w i t h t h e c o n v e nt i o n al h o r i zo n t a l - o r

v e r t i c a l - a x i s WECS.


14/24


15/24

SECTION 3 0

OSCILLATINGVANE UE S

L ik e t h e o s c i l l a t i n g c a b l e , t h e o s c i 1 1- at in g- va ne WE S has

i t s

o r i g i n s i n a n

undesirable phenomenon.

It

i s d i r e c t l y r e l a t e d t o t h e f l u t t e r plicnomenon t h a t

h as cau sed t h e d e s t ru c t i o n o f a number of a i r c r a f t , a l t h o u g h T ~ i o r n y c r o f t ' s

w ind mo to r p r op o s al h e a r s l i t t l e re se mb la nc e t o t h e f l u t t e r .

o f

a wing

131.

Again, the wind ene rgy approach has been t o enhance the phenomenon, r a t h e r

t h a n t o s u p p r e ss i t by m eans o f c o n ce p t s l i k e t h e o s c i l l a t i n g vane.

The ad van t ag e c l ai m ed f o r t h e o s c i l l a t i n g v an e

i s

t h a t i f t h e vane

i s

c a n t i -

l e v er e d f ro m a b as e , t h e n t h e most e f f e c t i v e p a r t , t h e t i p , i s i n t h e h i g h -

en e rgy a rea o f t h e f l o w fa r t h e s t f ro m t h e grou nd an d t h u s

i s

ae ro d y n am i ca l l y

m o s t e f f e c t i v e .

It

i s a l s o ar gu ed t h a t ( 1) t h e ~ n a i n a r t of t h e s t r u c t u r e

i s

i n v o l v ed i n t h e p r im ary ex t r ac t i o n o f p ower , ( 2 ) t h i s s t ru c t u r e can b e manu-

f a c t u r e d w i t h r e l a t i v e l y l ow - to le r an c e c o n s t r u c t i o n t e c h n i qu e s , ( 3 ) t h e power

conversion mechanism

i s

l o c a t e d a t g ro un d l e v e l , and

( 4 )

the concep t

i s

i n h e r e n t l y s e l f - s t a r t i n g .

T he m a jo r d i s a d v a n t a g e s of t h i s WECS a r e t h a t

( 1 )

b ecau s e

i t i s

a n o s c i l l a t i n e

s y s tem , t h e fo u n d a t i o n s must be d esi g n ed t o w i t h s t an d o s c i l l a t i n g l o ad s ; and

( 2 ) t h e po wer -co n ve r si o n s y s t en , whi ch u s e s t h e o s c i l l a t i n g m ot io n an d pro-

duces cons tan t - f requency

AC

power, coul d be expens ive.

R ie la w a h a s s t u d i e d t h e o s c i l l a t i n g - v a n e c o n ce p t [ 4 ] an d r ep o r t ed o n t h e

r e s u l t s of some t e s t s on a smal l model (Fi gur e 3-1). The measured power coef-

f i c i e n t s w er e q u i t e s m a l l , l e s s t h a n 0.1. The power l o a d i n g ,

Lp

was a l s o

low, wi th a maximum value of about 0.45. A s w i t h t h e o s c i l l a t i n g c a h l e, t h e

b l ad e a r ea r e q u i r e d f o r a g i v en power o u t p u t was much p re a t e r t h an t h a t

requ i red by conv en t io na l h igh- t ip -spee d-ra t io mach ines .

It seems r e a s o n a b l e t h a t f u r t h e r d e ve l op n en t work c o u ld b e done t o r a i s e t h a t

power c o e f f i c i e n t t o a ?:,re r e s p ec t ab l e v a l u e , and t h a t t h e power l o ad i n g

c o ul d a l s o be i n c r e a s e d

substantially. It i s

u n l i k e l y , ho we ve r, t h a t

i t w i l l

be p o s s i b l e t o r e a c h t h e t i p s p e ed r e q u i r e d t o m a i n t a i n a h i g h po we r- lo ad in g

c o e f f i c i e n t e v e n a t m o de r at e wind s p e ed s .

T h e o s c i l l a t i n g -v an e WE S can b e d i r ec t l y compared wi t h a v e r t i c a l - ax i s w in d

t u r b i n e (VAWT) ( F i g u r e 3 - 2 . Assuming t h a t , a t t h e same t i p s p e e d a nd t h e

same inaxirnum de f le c t i on , th e os c i l l a t i n g vane would have an aero dyna ~xicper-

f orm an ce s i m i l a r t o t h a t o f t h e a i r f o i l ( w hic h r o t a t e s ab ou t a p i vo t a t t h e

bas e) , and th e maximum ac ce le ra t i on s and s t r e s s e s would be s i m i l a r , t h e t w o

b l a d e d e s i g n s w ou ld b e q u i t e s i m i l a r . However, a s l o n g a s t li e t i p - s p e e d r a t i o

i s s u f f i c i e n t l y h i g h , t h e r o t a t i n g v a ne do e s n ot n eed

a

c y c l i c p i t c h c o :l tr o l

t o a c hi e ve

reas o r i ab l e ae ro d y n am i c e f f i c i en cy

It ap p ea r s t h a t t h e d es i g n and m an ufac tu re of a t ap e red v ane t h a t c an t s o u t -

wards a t an an g l e o f 45' f rom t h e base and ha s a

t i p

s o l i d i t y nf

i . 5

wg,.??d

n ot b e d i f f i c u l t f o r t i p s pe e ds o n t h e o r d e r of 30.5

m / s 10;1

f t / s ) . 1.f t h a

r o t a t i n g v a n e i s co m p ared wi t h an o s c i l l . a t i r l ~ :vane

t lat

o p e r a t e s tlhrouz'i a

rang e of f45" a t th e same maximum t i p sp ee ds , and th e vane c e s i f n

i s

s im-i l . a r ,


16/24


17/24

t he maximum s t r e s s l e ve l s due t o t he a c c e l e r a t i on would a l s o be s i a i l a r . Ho d

e v e r , w i t h a n o s ci 1 .L a ti n g v an e , t h e d i r e c t i o n o f t h e s c r e s s rt ? ve r se s

c y c l i c a l l y ; w i t h t h e r o t a t i n g v a ne , i t r e m ai ns c o ns t a n t , a l t hough t he a e r o -

dy nam ic f o r c e s a r e c y c l i c a l . The l o a d s o n t h e f o : ~ n d a t i o n s

7oul.d

h e s i;qi l. ar i n

magni tude i n bo th c as es , a l tho l igh wi-tli t h e o s c i l l a t i n g vane , th e fo rc es wou1.d

o c c u r i n o n e p l a n e.

I f

h ow ever, t h e o s c i l l a t i n g va ne

i s

des ign ed f o r omni-

d i r e c t i o n a l w in d s, t h e f o u n d at i o n s w i l l he s i m i l a r i n t he two c a s e s .

The

e s s e n t i a l d i f f e r e n c e b et we en t h e two s y s tt m s i s t h a t a n o s c i l l a t i n g v an e would

r e q u i r e a n e l a s t i c h i n g e an d an o s c i l l a t o r y power c o n v e r s io n n l e ch ~ ni s , ,w h i l e

a comparable VAW would have a ro ta ry be ar in g artd ro ta r y power con ver s ion

mechanism.

On b o t h t h e o s c i l l a t i n g v a ne an d t h e c om p a ra b le

V.4\7T

t h e d yn am ic f o r c e s a nd

moments can be reduced by th e use of tuned masses o r ba lan ce we igh ts , resp ec-

t i v e l y . R e ga rd in g t h e comparable

VAWT m eth od s a r e a v a i l a b l e t o d r a m a t i ca l l y

reduce t he bending moment on the vane and th e reb y reduce the c os t o f t h e

s t r u c t u r e . A l so , r o t a r y power c o n v e rs i o n d e v i c e s a r e more r e a d i l y

a v a i l a b l e .

It

a p p e a r s , t h e n , t h a t mo st of t h e a d v an t ag e s of t h e o s c i l l a t i n g

va ne a r e t h e same a s t h os e o f t h e c om pa ra b l e VAWT, a nd t h a t t h e r o t a t i ng va ne

h a s a d v an t a g e s t h a t t h e o s c i l l a t i n g v an e d o e s n o t ha ve .


18/24


19/24

SECTION 4.0

OSCILLATINGWING

WECS

It

a p p e a rs t h a t t h e o s c i l l a t i n g - u i u g s ys te n c o n ce p t o r i g i n a t e d i n t h e h el -i e f

t h a t m ax in un power c a n h e e x t r a c t e t i f ro m a l i f t i n g e l e m e nt i i t

i s

a l l ow e d

t o

rilove i n t h e d i r e c t i o n of t h e i f t f o r c e . On t h e s u r f a c e , t h i s

i s

a

v e r y r e a -

s o n a b l e :z ss:l mp tio n, s i n c e t h e work o n e i.s t h e f o r c e m u l t i p l ie d h v t h e

d-is-

tar ice t r a v e l e d i n tl le d i r e c t i o r : o f t h e f o r c e . Wit h t h e a i r f o i l , l ~ ow e ve r , h e

l i f t f o r c e

i s

normal t o t h e r e l a t i v e

velar-ity;

a n y n o t i o n n o rm a l t o t h e wind

c a u s e s a t i l t i n t h e l i f t v e ct o r . Assurning c o: ls ta nt l i f t c o e f f i c i e n t , t h e

ma gni tud e of t h e l i f t f o r c e i s p r o p o r t i o n a l

t o

t h e s q u a re

o f

t h e r e l a t i v e wind

speed .

A t

h i g h r e l a t i v e s p e e d s, t h e p o w er -e x~ ra ct in ): c a p a b i l i t y

of

a n

i s o l a t e d win g

i s

n e ar l y p r o p o r t i o n al t o t h e s q u a r e o f i t s r e l a t i v e s p ee d; i t

i s t h e n

noving

i n a d i r e c t i s n t h a t i s n e a r l y no rma l t o t h e l i f t v e c t o r .

Even i t h e b a s i c p re m is e i s n o t c o r r e c t , t h e o s c i l l a t i n g wing s ho u ld be

examined

3

i t s o m n e r i t s as a i-EGS. T t

i s

r e a s on a b l e t o h el i . ev e t h a t f o r

a

c a r e f u l l y d e si g n ed o s c i l l a t i n g v i n g , a power c o e f f i c i e n t c a n b e o b t a i n ed

t ;aC

i s

not much worse than th a t ob ta i i l ed f o r convenc iona . WECS. However , the

po wer i o a d i n g c o e f f i c i e n t x . il .1 b e d e p e n d e nt u p o ~ b o t h

t h e

s o l i t ' i i t y an d t h e

s pe ed r a t i o , 3 , e b e nd i ng mo nent s t h a t e x i s t as t h e d i r e c t i o n o f m o tl on i i :

r e v e r s e d

a c

t h e

l i n i t s

of t r a v e l i ~ i l i ove r n t h e maximum s pe e d a t t a i n a b l e .

R ence , a s i n o t h e r o s c i l l a t i n g co n c e p t s, a r e l a t i v e l y l a r g e , lo w--co st w ic g

i s

i n d i c a t e d .

To c o n v e r t t h e p ow er t o a u s e f u l f o m , some a r i v e n s y s t e m m u st

h e

a t t a c h e 5 t o

t h e wing. .Al though conce ptu a l mechanisms e x i s t , a r e l i a b l e . e f f i c i e n t power

co? ive rs i on mechanism must s t i l l

be

producsd a t

a

c o s t c o mp ar ab le t o t h a t o f

c o n v e n t i o n a l d e v i c e s .

T h e

3sc i . l l a t i i ;g -w ing

i n C S i s ana l oz o ; l s

t o t h e C i r o n i l l

[ 5 ] .

t ? lc s m e t o t a l

sc. .idi t y , :naxii::-m - t i ~ - - s r ; e ? d

ratio,^,

2nd o v s r a l i d i ~ e n a t o n s , h e a e r~ d yn a i r i

p ~ ~ ' ; : - r ~ i a n c ef

'i:e two dey; -iz?s s .oi?:ri

5e qs.i i te similar.

f d k e w i s e ,

a t

t i l e same

ri~:.::.nvz

~ i z g

P ~ ~ C ~ S

he

;naxF-v.>n dyrlanic Ioadi: an2 stresses shn ;? d

h e

si. :?iIar

". ;

f.,?t: .he < : i r v m i i i tiie

osc - : ;

l : . . ~ i n p~ . i i nc .~- ? owr.ver,

f o r t h e f i x e d- p i t 2 r;

G< r . = . ? ; : i . l 1 ar_c..c.lerat-ng f : : ~ c c s an: :


20/24


21/24

ST:

:>

. _

8:sciIZa 5r . i~-c lemi ;~t ._.

'YTCS

are

interest ing

e nz r gy - e x t r a c

tion

r ~ e c ? ~ a n i s m s .

TI . a :ey

a p p e a r

t o

have

no c l ea r -c i lt a d v a n t a ~ e over cor3parahle

r c r . z t i ng MECS;

n

f a c t , they a p pe ar t o have scme s i g n f f i c a n t d i sa d va n ta g es .

i int? c i tile ar jp l i : t . i l t~

n f ~ v o r

f

s u c h s:~scttns i s t h a t o s c i l . l a t i n g - e l e n e n t WECS

e: . lpl~y . ,

r

.

;:-.ea of low-cost m a t e r i a l , whfch r e p r e s e n t s an o v e r a l l c o s t

s a v i r ? . ~ v r t l?e s m l l e r , r e l a t i v e l y e xp en si ve m a t e r i a l now used. This

i s

ail

arg:in eni. tl:zt car, b e a p p l i e d e q u a l l y w e l l t o

IE S

sing r o t a t i n g e l e m e z t s , n

r o t a t i z q - e l e m e n t

I\ECS

i n f a c t , u s i n g r e l a t i v e l y s i na ll -s iz e, s o p h i s t i c a t e d

e i c n e n t s has

proven

t o

be

m ore e c onom i c a l l y v i a b l e t ha n u s i ng l a r g e - s i z e , low -

c o s t

. r? lmen ts .

S i nc e o s c i l l a t i ng - e l e m c n i . WECS d c n o t a p p e a r t o h a ve a ny s i g -

n i f i c a n t a dva r t t i z ge s O ve r e qu i va l e n t r c t a t i r : g - e l e m e n t WECS i t i s u n l i k e l y that

t h e y

c a n coi-i l~e

e w i t h c h e p r e s e n t g e n e r a t i o n o f c o n v e n t i o n a l wind e n e rg y

sys tems .


22/24


23/24

SECTION 6 0

REFERENCES

1. Payne,

P.

R . k o l i a n W i n d n i l l , U.S. Pa t e n t 4 , 0 2 4 ,4 0 9 , ? lay 17, 1977.

2 .

Payne,

P. R . A

T h e o r e t i c a l A n a l y s i s o f O s c i l l a t i n g C a b l e Wind E n e r w S y s-

te ms , SERI/TR-0-9173-1, Gol den ,

GO

S o la r Energy R e ~ a r c h n s t i t u t e ,

September 1951.

3 . Tnornyc rof t , J. I . Wind Mot or, U.S. P a t e n t 1,4 90, 787 , A p r i l 1.5, 1944.

4. Bielawa,

R.

L . Development of an O s ci l l a t i n g Vane Concept a s an Innova-

t i v e Wind En er w Convers ion Sys tem,

S E R I / T R - ? ~ ~ O ~ ~ - ~

olden, CO: S o l a r

Energy Resea rch In s t i t u t e , March 1982.

5. McConnell,

R.

D. G i ro m il l Overvi ew, SERI/TP-35-263, Golden ,

CO:

S o l a r

Energy b s e a r c h I n s t i t u t e , Play 1979.


24/24

Doc~ment

ontrol

1 SERI Report No 2. N i l s Access~onNo

3.

Recipient s Accession No

Page I SERI/TR-211-1911

I

I

4. Title and Subtttle

5.

Publication Date

December 1983

Osc i 1 a t i n g Wind Energy C onvers ion Sys tems

I

I

7 Author(s)

8 Performing Organization Rept. No.

12 Sponsoring Organization Name and Address

13. Type of Report Period Covered

P e t e r S o ut h, R i c k M i t c h e l l

9. Performing Organization Name and Address

S o l a r E n e r g y R e s e a r c h I n s t i t u t e

1617 Co le Bou levard

Go1 den, Co lor ad o 80401

T ec hn i c a l R epo r t

14.

15. Supplementary Notes

10. ProjecVTask/Work Uni t NO.

1067.10

11. Contract (C) or Grant (G) No

(C)

16. Abstract (Limit: 200 words)

The i n f o r m a t i o n i n t h i s d ocu me nt s u g ge s ts t h a t O s c i l l a t i n g W ind E n er gy C o nv e rs io n

S yste ms d o n o t a p p e ar t o h a ve an y s i g n i f i c a n t a d va n ta g es o v e r e q u i v a l e n t c o n-

v e n t i o n a l r o t a t i n g - e l e m e n t w i n d e n er gy c o n v e r s i o n s ys te ms . I n f a c t , i n m os t

cases

i t

appears t h a t th ey have seve ra l d i sad van tage s . The document addresses

t h e o s c i l l a t i n g c a b l e - t yp e w i nd e ne rg y co n v e rs i o n s ys te m as w e l l as t h e o s c i l -

l a t i n g vane and t h e o s c i l l a t i n g w i ng .

The advantages and d isadvan tage s o f each

t y p e o f s y st em a r e ev a l u a t ed , and i n eac h c ase a . c om pa r i s on i s made bet ween

i t

and a c o n v e n t i o n a l r o t a t i n g - e l e m e n t w i n d en e r g y c o n v e r s i o n d e v i c e .

t

appears

u n l i k e l y t h a t a ny o f t h e o s c i l l a t i n g e le me nt c o n ce p ts c an compete w i t h t h e

p r e s e n t g e n e r a t i o n o f c o n v e n t i o n a l w i n d e n e r gy s ys te m s.

17 Document Analysis

a.Descriptors

irfoils Cables Girornill Turbines Oscillations Power

Coefficient Vanes Wind Power Wind Turbines

b. Identifiers/Open-Ended Terms

I

c. UC Categories

U.S. Dep artmen t o f Commerce

5285 Port Royal Road

S p r i n g f i e l d , V i r g i n i a 22161

.

20. Price

18. Ava~labilityStatement

N a t i o n a l T e c h n ic a l I n f o r m a t i o n S e r v i c e

19. No. of Pages

25

oscillating wind energy conversion system

Documents