introduction to ocean wave conversion.falcon/wt/ihptalks/babarit.pdf · laboratoire de mécanique...

Institut Henri Poincaré – Wave Turbulence Workshop - April, 10th, 20091

Introduction to Ocean

Wave

Energy

Conversion.

Aurélien Babarit

Hydrodynamic and Ocean Engineering Group

Laboratoire de Mécanique des Fluides (CNRS UMR 6598)Ecole Centrale de Nantes


Outline

> Introduction

> Ocean wave energy : resource

> Wave energy converters : a review of the technology.

> Current issues.

> The full scale test site : SEM-REV


The

Hydrodynamic

and

Ocean

Engineering Group

Hydrodynamic and Ocean Engineering GroupStaff : 39/19, Head : Bertrand Alessandrini

Laboratoire de Mécanique des FluidesStaff : 88/37, Director : Alain Clément

EMCI EMN DAH

• Free surface flows• Scale of floating structures (ships, offshore platforms)• Numerical and experimental approaches

Tools :

Numerical tanks Bassins numériquesExperimental tanks Full scale test site

Expertise :

Research interests :• Ocean wave modelling and propagation• Performances (ship resistance, seakeeping, manoeuvrability)• Impact – Violent Flows.• Marine Renewable Energy


Marine Renewable

Energy

Tidal Energy.

The Rance’s barrage, 240MWc

Marine Current Energy.

Seagen, 1.2MWc

Ocean Wave energy.

Pelamis, 750MWc

Offshore Wind Energy.

Hywind, 5MWc

Pacific OTEC, 5MW © OCEES International

Ocean Thermal Energy.

Osmotic energy.

Statkraft, 20 MWc

Estimation of the harnessable energy = 120 000 TWh/an. Source International Energy Agency.


Ocean Wave Energy : Resource


Ocean

waves

> Sun Wind Ocean waves

> Measurement

Sea surface of hurricane Isabel© Mike Black @ NOAA


Ocean

waves

Wave> A random phenomenon

FT

Wave energy spectrum :> Steady on a hour scale> Parameters :

• T1 peak period• H13 significative height

T1 (s) H1/3 (m) P (kW/m)

6 1 2.4

9 2.5 22.5

17 14 2500Measured during Hurricane Katrina


Estimation of

the

Wave

Energy

Resource

> Power available by wave front in a given sea state (T1 , H13 ) :

> Scatter diagram of probabilities of occurrence C (T1 , H13 ) of sea states at a given location • From met-ocean models.• From measurements (datawells, waveriders)

over several years

> Mean annual power available on a given state : île d’Yeu (46°41.45‘N / 2°25.65'W)

( ) 23/113/11 4.0, HTHTPwave =

( )( )∑>=<

3/11 ,

23/113/11,4.0

HTwave HTHTCP


World wave

energy

resource

Estimation of the harnessable wave energy ~20000 TWh/an (International Energy Agency)


Wave energy converters.


Wave

energy

conversion

> Started in the 70’s (first and second oil crisis)

> Almost stopped in the 80’s (cheap oil again)

> Re-started in the beginning of the 90’s.

> At the moment, more than 60 projects (technologies) in development around the world (mainly Europe)


Three

main categories

> Oscillating Water Columns (OWC)

> Overtopping systems

> Wave activated bodies

+ uncommons…

LIMPET (500kW)

pelamis (750kW)

Seawave


Configurations

Attenuator

Terminator

Point absorber

λ = wavelength, ~50 à 150 m


Overtopping

systems

> Principle


TAPCHAN (Norvège)

> Built in 1985, close to Bergden> 350 kW> Stopped in 1991


TAPCHAN


Seawave

Slot-cone

Generator

(Norvège)

> 1/15 model tested in 2005


Wavedragon

> Prototype : ¼ scale> 237 t> 20 kW


Wavedragon


Oscillating

Water

Columns

> Principle :

LAND


The

Pico plant (Azores)

> Wells turbine

> 400 kW

> 12x12 m chamber

> Production : 0.54 GWh/an

> 1.3 M€

> 0.23 €/kWh


LIMPET

> Construction


OWC in a harbour

> Sakata harbor (Japon)


OWC in a floating

structure

OSPREY 2000

2MW

WAVEGEN UK

OSPREY 2000

2MW

WAVEGEN UK

Energetech (Australie)

Sperbuoy (UK)

The mighty whale (Japon)

BBDB (Irlande)


Wave

activated

bodies wave

energy

converters.

> Salter’s duck (1983)> 14 m diameter, 90 m long, 11000 t


Mc

Cabe

wave

pump

(Ireland)

> Application to dessalinasation> 1996, 40 m long> 60 kW ~ 300000 m3/an, 0.2€/m3


AWS (Pays bas)

DémonstrateurÉchelle 1/1

2MW

Mise à l’eau été. 2004Leixoes(Portugal)

> Direct drive


Pelamis

(Ecosse)

> 4 x 30 m, 3.5m diameter – 750kW> Hydraulic Power Take Offs


Pelamis

(Scotland)

1/20 scale model test at Ecole Centrale de Nantes (every year since 2003)

1/7 scale model test


Pelamis

(Scotland)

March 2004

April 2004: first full scale trials at sea

Since september 2008: first commercial wave energy power plant connected to the grid in Portugal


SEAREV (Nantes)

> Principle :• A moving mass in a closed buoy• Relative motion is used to drive a Power

Take Off.> Advantages :

• Closed system, all moving parts are dries• Internal reference.• No end stops : the moving mass is a

cylinder with an off centered gravity center.

> The relative motion is controlled.

> 2 patents (2006, 2008, property of CNRS)

> Collaborations

Yoke

Hull

Heavy

cylinder


Artistic

view

Hull

Cylinder

Hydrauliccylinders

HP accumulator

Hydraulic motor Generator

Electric cable

BP accumulator


Numerical

models

> Frequency and time domain> Linear and non linear hydrostatic and Froude

Krylov forces (calculation on the exact wetted surface).

> Linear and non linear moorings.> Fluid structures interactions using potentiel

theory


The

SEAREV model

+ Measurement of the incident wave using wave probes+ Motion tracking system using video cameras (Qualisys).+ Brakes for application of the latching control.

Electrical motor Inertial measurement unit

Cylinder

Buoy

Measurement of the relative motion


The

Hydrodynamic

and

Ocean

Engineering Wave

Tank

Dimensions: 50 x 30 x 5 m + Pit 5x5x10m

48 PC-controlled flaps (electrical motors)

Reflected waves absorption (wavemaker)

Motion tracking system

Parabolic-shape stainless-steel beach

T = 0.5 ~ 5 s

Hmax ⁄

2 mIrregular and regular waves

Unidirectional and crossed waves


Tank tests

> Two sets of tank tests in 2006.• Scale 1/12.• Development of control algorithms.• Validation and calibration of numerical models.

> New experiments.• New design• Scale 1/25th • Experiments on moorings and survivabilities

issues.


Measured

transfer

function


Towards

a full scale

prototype

> Technical feasbility proven in 2007.

> Towards a full scale prototype.

• 25 m, 1000 t.> Looking for industrial

partners.


> A powerful resource

> Many (too much?) technologies in development• No consensus on the technological solution (contrarily to land based

wind energy).

> First (pre) commercial plant at sea (25c€/kWh)

> Many technical and scientific issues remain to be tackled to bring costs (and risk) down.

Summary.


> Scientific issues :

Wave

energy

converters

Hydrodynamicprocess

Power TakeOff

ResourceMechanicalEnergy Electricity

Wave energy converters

Seakeeping : large amplitude of motions

Interactions in arrays of wave energy converters

…

Direct drive

Storage and smoothing of the power

…

Control - command

Optimal control

Control strategies for arrays

Strong coupling

Sea state description

Wave prediction

Main area of ourresearch activites

Collaborations


The full scale test site : SEM-REV


The

SEM-REV facility

: Full scale

test site

ECNLaboratory

Wave EnergyGrid connectedTest centre


• one berth, grid connected (2.5 MW)• 30m water depth, flat and sandy bottom• 1 km2 fully instrumented sea area (ADCPs, waveriders buoys, HF radar, …)• radio link (data) to the onshore base

• Budget : 5.5 M€• Operational in 2010

Characteristics


Thank

you

for your

attention

« Utilisez la nature, cette immense auxiliaire dédaignée. (…) Réfléchissez au mouvement des vagues, au flux et reflux, au va-et-vient des marées. Qu'est-ce que l'océan? une énorme force perdue. Comme la terre est bête! Ne pas employer l'océan! »

Victor HUGO, Quatre-vingt treize (1874)

Books on wave energy :

• Falnes J., 2000, Ocean Waves and Oscillating Systems : Linear interactions including wave-energy extraction, Cambridge University Press

• Cruz J., 2008, Ocean Wave Energy : Current Status and Future Perspectives, Springer.


Latching

control


Seakeeping

: Large amplitude of

the

motion

> Usual methodology for designing offshore structures (platforms, off-loading buoys, …)

PrototypeTank testingNumerical simulation

Virtual mode Small scale model (1/20) Full scale

> Methodology inadapted in case of wave energy converters, because :• Linearity assumptoins.• Wave energy converters are designed by purpose for large amplitude of motions.

> Standard CFD tools are non satisfactory:• CPU time : 1day / wave period. • Inaccuracy in modelling and propagating ocean waves, especially in random waves.

New class of numerical methods, based on potential theory under weak-scatter assumptions.


Temps adimensionnel

Ang

lede

tang

age

(°)

0 0.2 0.4 0.6 0.8 1-20

-10

0

10

20

Potentiel linéaireIcareExperience

Large amplitude of

the

motion : SWENSE approach

> Improvement of the accuracy

> CPU time is long : ~semaine.

Green : ExperimentsBlue : Linear theoryRed : RANSE solver


Wave

interactions in large arrays

of

wave

energy

converters

> Wave interactions between systems can be :• destructive : masking effects.• constructive : focusing.

> Issues : • (Very) large arrays (>10)• Environmental impacts.

Experimental model Comparison between experiments and numerical model

introduction to ocean wave conversion.falcon/wt/ihptalks/babarit.pdf · laboratoire de mécanique...

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