Abstract: To alleviate energy crisis and environmental degradation and enhance the development and use of renewable energy, this study develops a numerical model of a semi-submersible multi-floating body wave power plant through combining wave energy conversion technologies of point absorption and raft type. The device is mainly composed of a central floating platform, an array of oscillating floats, a hydraulic system, and structure connecting floats to the platform, and collects wave energy from the oscillating floats on the sea surface. To improve its collecting efficiency, we numerically simulate and examine its energy conversion using AQWA hydrodynamic simulations, and analyze the frequency domain responses of a single float with different values of parameters such as the mass, size, and structure of the floats. And a detailed analysis is made on the time domain responses of a single float and the whole device under sea conditions of wave height of 1 m and wave periods of 5 s and 3 s. The results show that the geometry of the underwater part of the float has a great influence on its added mass and wave excitation force, and that a cylindrical float of 2 m in diameter features larger amplitude of vertical oscillations. This suggests that in the condition of low wave frequencies, the floats with such a design can capture wave energy closer to the maximum extent, thereby improving overall efficiency. For the floats working at high wave frequencies, they should have a conical shape, the diameter increased appropriately, and the weight reduced so as to capture more wave energy. By optimizing float structure, the energy collection efficiency of the device is raised by about 95%, indicating the importance of float structure in efficiency improvement.

Key words: wave energy, hydrodynamic performance, semi-submersible, multi-floating, oscillation buoy