1. NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. MEDA Model 5 – Bottom-hinged pitching wave energy system design and analysis Ye Li – NREL Yi-Hsiang Yu– NREL Robert Thresher – NREL MEDA Model Meeting State College, PA August 23-24, 2011

2. NATIONAL RENEWABLE ENERGY LABORATORY Presentation outline 2 Concept definition Computational fluid dynamics (CFD) hydrodynamic modeling

3. NATIONAL RENEWABLE ENERGY LABORATORY Background: several developed device concepts 3 BioWaveWaveRoller Oyster

4. NATIONAL RENEWABLE ENERGY LABORATORY Several design variables need to be considered 4 Dimensions and Shape Flap height (including the part is above the mean water surface) Flap thickness (buoyancy induced pitching stiffness) Flap width (3D effect) Flap edge shape (3D effect) Design water depth Structural integrity

5. NATIONAL RENEWABLE ENERGY LABORATORY Device design 5 The device design was obtained from Sandia National Lab *Overview of Large Dimensions Device is attached to the seabed and designed to operate in water depths of 20-25m.

6. NATIONAL RENEWABLE ENERGY LABORATORY Modeling Plan 6 Potential code modeling (WAMIT or other BEM code) for basic geometry and thickness designs CFD simulations (FVM or SPH) for more detail analysis. Validation with experimental test Optimization based on hydrodynamic analysis results

7. NATIONAL RENEWABLE ENERGY LABORATORY Numerical Settings for CFD Simulation 7 Water surface Sponge-layer damping zone Seabed Mean water Depth = 25 m Incident waves: Wave height=4m Wave period=10sec Plate size: Height=10m Thickness=2m Supporting arm currently was not included in the CFD simulation

8. NATIONAL RENEWABLE ENERGY LABORATORY Computational Grid 8 Preliminary computational grid is very coarse (N≈45,000), and a grid refinement study is planned.

9. NATIONAL RENEWABLE ENERGY LABORATORY Preliminary Result 9 Wave condition: H=4m; T=10 sec The top of the flap is 1.25m below the mean water surface. Maximum normal forceMaximum pitch angle 15 kN/per unit width10 degrees

10. NATIONAL RENEWABLE ENERGY LABORATORY Smooth Particle Hydrodynamics 10

11. NATIONAL RENEWABLE ENERGY LABORATORY Discussions 11 In the current preliminary design, wave energy may be lost due to the cap between the water surface and the flap. To accurately predict and investigate the performance of this type of wave energy device( with extreme wave breaking and overtopping), CFD simulation is needed. Experimental test must be conducted in parallel with the numerical method development to ensure the quality of the design