The performance of a wave energy converter in shallow water

The performance of a wave energy converter in shallow water PowerPoint PPT Presentation


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A surging point absorber in shallow water. kD < 1.0. . . . . kh < 1.0. . . . An ideal point absorber. Power capture = Pi . ? / pTypical seaT = 10 secs, Pi = 50 kW/mPower capture

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The performance of a wave energy converter in shallow water

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1. The performance of a wave energy converter in shallow water Matt Folley Trevor Whittaker Alan Henry

2. A surging point absorber in shallow water

3. An ideal point absorber Power capture = Pi . ? / p Typical sea T = 10 secs, Pi = 50 kW/m Power capture ˜ 2.5 MW 2.5 MW » power capture of any projected point absorber

4. Effect of motion constraints Power capture, P = Pmax(2r-r2) r = X / X0 X0 = F / 2?B Pmax = F2 / 8B F = wave force, B = hydrodynamic damping P = 0.5 F?X (1 – r/2) Power capture proportional to wave force for highly constrained motion

5. Effect of viscous losses Power capture, P = F2 / 8(B + Bv) Bv = viscous damping coefficient Power capture proportional to wave force squared as B / Bv ? 0

6. Long wave approximation of surge wave force Wave force proportional to horizontal water particle acceleration Horizontal acceleration increases with reduction in water depth x = horizontal water particle amplitude, y0 = deep water particle amplitude, kh = non-dimensional water depth

7. Surge wave force ratio

8. Effect of water depth on incident wave power Reduction in incident wave power due to seabed friction and wave breaking Department of Energy nearshore wave energy resource study (1992) indicates that the reduction in incident wave power for commonly occurring sea-states from a water depth of 40 metres to 10 metres is typically about 10% The larger difference in average annual incident wave power is due to a greater reduction in rarely occurring, highly energetic sea-states that contribute disproportionately to the average annual incident wave power

9. Comparative performance of a surging point absorber in deep and shallow water Flap-type wave energy converter Flap width = 12.0 metres Flap draft = 10.5 metres Flap thickness = 1.0 metres Flap natural period = 12.0 seconds Shallow water depth = 12.0 metres Deep water depth = 50.0 metres Reduction in wave power = 20% Quadratic viscous drag coefficient = 388 kNs2/m2

10. Equations of motion

11. Power capture with linear damper

12. Power capture with complex conjugate control

13. Power capture with reduced viscous losses, CD = 100 kNs2/m2

14. Power capture with shallow water incident wave power reduction of 50%

15. Conclusions Power capture depends on incident wave force for small surging WEC’s Surge wave force is larger in shallow water due to increased horizontal water particle motion Incident wave power of commonly occurring sea-states not dramatically reduced by water depth Small surging WEC’s typically have a higher power capture in shallow water

16. Further work Improved modelling of the reduction in incident wave power reduction with water depth Wave-tank modelling of WEC power capture in deep and shallow water

17. Power per unit volume (CCC)

18. Capture factor (CCC)

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