Sensitivity analysis of geometric characteristics on the cavity-buoy for energy capture efficiency enhancement of a semi-submersible floating-array-buoy wave energy converter system

To investigate the conditions where wave energy resource is sparse, a novel semi-submersible floating-arraybuoy wave energy converter (SFABWEC) system was proposed. This system integrates oscillating-array buoys with a semi-submersible floating platform. Geometric characteristics of the energy-capturing mechanisms, cavity-type oscillating-array buoys, were sensitively analyzed to improve the wave energy capture performance. Herein, the effects of different cavity-buoy geometries and the geometry-influenced hydrodynamic coefficients on the motion response and energy capture efficiency of the SFABWEC were evaluated through frequencydomain and time-domain analysis considering regular and irregular waves. A mathematical model was developed to calculate the primary efficiency of buoy-capturing wave energy, and the optimization model was established by comparing the root-mean-square (RMS) efficiency performances of different models. The results show that cavity-buoy with a frustum cone-bottom cylindrical shape, relatively larger size (a diameter of 2.8 m), and larger mass (8070 kg) exhibited higher energy capture efficiency for the given wave condition. With coupled power take-off (PTO) damping, the RMS wave energy capture efficiencies of the optimal-geometric cavity-buoy can reach 18.84% in regular waves and 17.39% in irregular waves, offering significant improvement over the basic model. The numerical results were validated by the experimental results of the test rig provided.