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
2015/08/04
1
Introduction
• 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)
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The SWEC
Submerged SWEC ‘V’ (adapted from Retief et al., 1982)
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The SWEC
SWEC during crest of the wave (Bavesh, 2006)
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The SWEC
SWEC during trough of the wave (Bavesh, 2006)
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Problem Statement
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
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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
• 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
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Experimental testing
CAD drawing of model.
Photo of experimental setup
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Surface SWEC configuration
Schematic of Surface SWEC configuration
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Submerged SWEC configuration
Schematic of Submerged SWEC configuration
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Experimental testing
 (t)× p(t)
Pconverted (t) = V
Pwave =
gH
8
(Zhang et al., 2012)
2
Cg
(McCormick, 1981)
P converted
=
Pwave
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Mathematical modelling
Linear wave theory
Trapped air cavity theory
Newton’s second law
Ideal gas law
Isentropic relationship
Head loss equation
Energy equation for pipe flow
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Results – Surface SWEC
Inner chamber surface level: z
0.04
0.03
0.02
Experimental
0.01
z(m)
Simulated
0
10
12
14
16
18
20
22
24
-0.01
-0.02
-0.03
H: 0.06m
T: 2.5s
Time (s)
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Results – Surface SWEC
Pressure difference between chambers
250
Measured
200
Simulated
150
Delta P (pa)
100
50
0
-50
11
12
13
14
15
16
17
18
19
20
21
-100
-150
-200
-250
Time (s)
H: 0.06m
T: 2.5s
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Results – Surface SWEC
Efficiency - 0.25% Plate
20
Measured - H:0.06
Simulated - H:0.06
n (%)
15
10
5
0
1.25
1.5
1.75
2
2.25
2.5
2.75
3
3.25
T (s)
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Results – Surface SWEC
Efficiency - 0.5% Plate
35
Measured - H:0.06
30
Simulated - H:0.06
25
n (%)
20
15
10
5
0
1.25
1.5
1.75
2
2.25
2.5
2.75
3
3.25
T (s)
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Results – Submerged SWEC
Efficiency - 0.5% Plate
25
Measured - H:0.09
20
Simulated - H:0.09
n(%)
15
10
5
0
1.25
1.5
1.75
2
2.25
2.5
2.75
3
3.25
T(s)
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Results – Submerged SWEC
Efficiencies - 1% Plate
25
Measured - H:0.09
20
Simulated - H:0.09
n(%)
15
10
5
0
1.25
1.5
1.75
2
2.25
2.5
2.75
3
3.25
T(s)
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Results – Submerged SWEC
Varoious orientations - H: 0.09 - 0.5% Plate
20
Orientation 1
Orientation 2
Orientation 3
Orientation 4
Orientation 5
n(%)
15
10
5
0
1.25
1.5
1.75
2
2.25
T (s)
2.5
2.75
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3.25
20
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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