Theoretical Investigation on an Oscillating Wave Energy Converter in Different Degrees of Freedom in Front of a Seawall

The interaction between regular waves and an oscillating wave energy converter (WEC) in front of a vertical seawall is investigated using a 2D analytical model. A three-degree of freedom (DOF) WEC and a WEC hinged to the seawall (constrained to pitch mode) are considered to examine the influence of the DOF of the WEC on the wave energy extraction performance. Results show that the piston-mode water resonance in the gap and the coupled WEC and water column resonant motion significantly influence the wave energy extraction efficiency. At low frequency, the case with a 3-DOF WEC has a broader high-efficiency bandwidth than that with a heaving WEC. However, 3-DOF WEC exhibits worse performance at high frequencies. The frequency response of the wave energy capture width ratio (CWR) for the pitching WEC case shows a trimodal trend under the specified conditions. It showcases the best overall wave energy extraction performance in terms of the high-efficiency bandwidth. Furthermore, a parametric study indicates that the gap distance between the WEC and the seawall has tremendous effects on the CWR of both cases. As the position of the hinge point of the pitching WEC changes, the CWR at the low and high frequencies shows opposite trends.