The Oscillating Wave Surge Converter

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-Professor Trevor Whittaker FREng. -Dr. Matt Folley
26 – 05 - 2005 Queen’s University Belfast

 Wave resource & characteristics

 Design challenges & options
 Examples of wave power systems

 Essential wave power plant features
 Case study – OWSC

 The way forward
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Global wave resource

Average annual wave resource kW/m deep water
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European wave resource
European Resource 400 TWh 17% of EU UK Resource

61-87 TWh
20% of load

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Characteristics of waves
Deep water

Shallow water

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Design challenges in wave energy
 Convert KE & PE in waves to useable form
 Elliptic fluid particle motion – large cyclic forces  Irregular frequency, amplitude, direction  Extreme loads can be > 100 x average working

 Wave power converters must
 Survive extremes  Produce a predictable defined output  Compete with other forms of generators  Have a substantial positive energy balance
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Configuration options & design choices
moving structure - relative to sea bed

Frame of
fixed structures - moving water relative motion of components

Power conversion
hydraulic mechanical pneumatic

Device types
Terminators Point absorbers Attenuators
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Pelamis - raft, array, attenuator
•Relative motion between floats

•attenuator line array
•high pressure hydraulics •active stiffness control

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Archimedes Wave Swing
• Sea bed mounted • Point absorber

• Linear generator

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Wave Dragon
• Reaction - physical size
• Low head hydro PTO • Physical focusing • Energy storage

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• Sea bed reaction • Physical focusing • Oscillating water column

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Wave Powered Navigation Buoys

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QUB 75 kW Device -Islay
• 1st UK Shoreline Device • Islay, Scotland • 75 kW Capacity • Successful Prototype

1988 - 1999

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Schematic of LIMPET

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LIMPET shoreline OWC

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Desirable characteristics for WEC’s
 For economic energy production
 Primary wave/body interface a good wave-maker
Most common waves Progressive decoupling as waves increase

 Avoid extreme loads in storms
Intrinsic ‘fail safe’ response Can’t afford structure to resist extremes

 Short direct load paths
Maximise structural efficiency Minimise material used

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Desirable characteristics for WEC’s – cont.
 Appropriately broad bandwidth response
Multi resonance, slow tuning, phase control Better accommodation of variation in seas

 Highest efficiency in most common seas
More consistent energy production throughout year Maximise use of installed capacity Generation in extreme seas at very low efficiency

 System not site specific & mass produced
Standardised design and production
Wide availability of sites

 Easy to service
‘plug & play’ whole or part Queen’s University Belfast

OWSC evolution - application of desirable characteristics
 EPSRC funded research (shoreline top hinged)
(1st April 03 to 30th Sept. 05)

 QUB – concept development experimental test programme
 MMU – numerical modelling  QUB/MMU – design guidance  2D testing in progress  Initial 2D numerical models working  PIV measurement and 3D testing in progress

 Concept evolution
 Bottom hinged nearshore
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Logic of concept evolution
 Top hinge – embedded shoreline device
 A natural development from LIMPET  Direct load path, waves – flap – hinges – rock on either side of gully

 Can ‘park’ in air out of storm waves
 Installation, maintenance above sea level, no underwater construction

 Niche markets only due to limited number of sites
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Logic of concept evolution
 Bottom hinge – embedded shoreline device
 No performance advantage over top hinge

 More difficult construction & maintenance
 Limited number of shoreline sites

Shoreline devices are better top hinged More commercial potential with nearshore devices
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Logic of concept evolution
 Top hinged nearshore
 Not an optimum nearshore concept due to structure required for long load path, up to hinge then down to sea bed

Bottom hinged flap has shortest load path and hence minimum structure

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Logic of concept evolution
 Bottom hinged nearshore – back wall
 Most suited to terminator configuration
Back wall eliminates transmission Increases efficiency in 2D

 Back wall little advantage in line array configuration 3D

Every component must pay for itself

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Nearshore OWSC
 Bottom hinged nearshore
 Simple wave power configuration  Reasonable point absorber efficiency  Excellent potential for survivability  Direct load transfer into sea bed

Focus of current research

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OWSC-B model

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Queen’s University Belfast

Optimum damping for 6 standard seastates
0.7 Te = 13secs Pi = 40kW/m Te = 10secs Pi = 40kW/m Te = 10secs Pi = 20kW/m 0.6 Te = 10secs Pi = 10kW/m Te = 7secs Te = 7secs 0.5 Pi = 20kW/m Pi = 10kW/m

Capture Factor





0 0 500 1000 1500 RMS Torque (kNm) 2000 2500 3000

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Power capture for OWSC
180 160



Power (kW)






0 Te = 7secs Pi = 10kW/m Te = 7secs Pi = 20kW/m Te = 10secs Pi = 10kW/m Te = 10secs Pi = 20kW/m Te = 10secs Pi = 40kW/m Te = 13secs Pi = 40kW/m

Sea State

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Effect of tidal range on performance
0.8 0.7 0.6
Capture Factor

0.5 0.4 0.3 0.2 0.1 0 Te = 7secs Te = 7secs Te = 10secs Te = 10secs Te = 10secs Te = 13secs Pi = 10kW/m Pi = 20kW/m Pi = 10kW/m Pi = 20kW/m Pi = 40kW/m Pi = 40kW/m Sea State

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Queen’s University Belfast

Queen’s University Belfast

Model tests show that essential criteria can be met
 Bottom hinged flap most common type of wavemaker
 Avoids extreme wave loads in storms
Decouples as rotation increases

 Direct load path – minimal structure
Wave flap hinges/ rams sea bed

 Broad bandwidth response
Ideally suited to slow tuning and phase control

 Highest efficiency in most common seas
In 10m depth naturally tuned to 10s

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Wave power – the way forward
 Agree essential criteria to select systems  Concentrate on 2 or 3 systems in total for offshore, nearshore and shoreline locations
 Funding spread too thinly at present– much is wasted on designs which
could never be economic
have too much embedded energy would not survive storms can not be serviced economically

Queen’s University Belfast

Wave power plants need to demonstrate
 Cost effective energy generation  Availability of output
 Consistency of wave climate  Reliability/serviceability of wave power plant

Resource utilisation is not an objective now or in the near future

Queen’s University Belfast

In conclusion
 Wave energy is a significant resource
 To date wave power conversion has been demonstrated technically but not economically  We believe economic wave power systems can be developed
 but the industry will have to focus not diversify

 A set of essential characteristics is proposed and a system which meets the criteria presented

Queen’s University Belfast

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