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Modelling and Design of an Oscillating Wave Energy Converter
Jason Fairhurst
Supervisor: Prof. JL Van Niekerk Department of Mechanical and Mechatronic Engineering,
Stellenbosch University 13 July 2015
Introduction
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• The SWEC born in 1980’s
• Estimate of 25 kW/m along South Africa’s West coast 700 km long
• Other WEC’s and claimed conversion efficiencies:
Archemides Wave Swing - 50% (Fiaz and Salari, 2011)
Oscillating surge converter – 60% (Folley, 2004)
OWC , Limpet – 60% (Wittaker et al., 2004)
Over-topping device – 18% (Tedd, 2007)
Pelamis – 70% (Yemm et al., 2011)
The SWEC
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Submerged SWEC ‘V’ (adapted from Retief et al., 1982)
The SWEC
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SWEC during crest of the wave (Bavesh, 2006)
The SWEC
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SWEC during trough of the wave (Bavesh, 2006)
Problem Statement
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Past studies have not been able to accurately
model the SWEC:
Not able to produce accurate results for high frequency wave inputs
An unaccounted-for loss variable has often been added
Objectives
• Extensive experimental testing:
Use results to verify simulation models
Make conclusions on the viability of the SWEC as a WEC and the affect of orientation angle
• Produce two verified simulation models:
Surface SWEC
Submerged SWEC
Use models to optimise chamber design
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Methodology
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• Scale model of a single SWEC chamber
• Measurement apparatus: Orifice flow meter – 5 different plate sizes
Wave probes
• Test two configurations in Civil engineering wave flume
• Develop simulation models for two configurations
• Verify simulation models
• Optimise chamber
• Draw conclusions
Experimental testing
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CAD drawing of model. Photo of experimental setup
Surface SWEC configuration
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Schematic of Surface SWEC configuration
Submerged SWEC configuration
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Schematic of Submerged SWEC configuration
Experimental testing
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p(t)×(t)V =(t)P converted
gC8
gH =P
2
wave
wave
converted
P
P =
(Zhang et al., 2012)
(McCormick, 1981)
Mathematical modelling
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Linear wave theory
Trapped air cavity theory
Newton’s second law
Ideal gas law
Isentropic relationship
Head loss equation
Energy equation for pipe flow
Results – Surface SWEC
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-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
10 12 14 16 18 20 22 24
z(m
)
Time (s)
Inner chamber surface level: z
Experimental
Simulated
H: 0.06m T: 2.5s
Results – Surface SWEC
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H: 0.06m T: 2.5s
-250
-200
-150
-100
-50
0
50
100
150
200
250
11 12 13 14 15 16 17 18 19 20 21
De
lta
P (
pa)
Time (s)
Pressure difference between chambers
Measured
Simulated
Results – Surface SWEC
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0
5
10
15
20
1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25
n (
%)
T (s)
Efficiency - 0.25% Plate
Measured - H:0.06
Simulated - H:0.06
Results – Surface SWEC
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0
5
10
15
20
25
30
35
1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25
n (
%)
T (s)
Efficiency - 0.5% Plate
Measured - H:0.06
Simulated - H:0.06
Results – Submerged SWEC
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0
5
10
15
20
25
1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25
n(%
)
T(s)
Efficiency - 0.5% Plate
Measured - H:0.09
Simulated - H:0.09
Results – Submerged SWEC
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0
5
10
15
20
25
1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25
n(%
)
T(s)
Efficiencies - 1% Plate
Measured - H:0.09
Simulated - H:0.09
Results – Submerged SWEC
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0
5
10
15
20
1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25
n(%
)
T (s)
Varoious orientations - H: 0.09 - 0.5% Plate
Orientation 1
Orientation 2
Orientation 3
Orientation 4
Orientation 5
Conclusions
• Experimental results show maximum conversion efficiency of 15% and 13% at operating conditions
• Reaching up to 17% orientation 2 not at operating conditions
• Both models predict conversion efficiency with +- 2% average error
• Optimisation still to be carried out
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Thanks
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