Modeling and Experimental Investigation on Performance of a Wave Energy Converter with Mechanical Power Take-Off

Abstract

This paper presents an experimental investigation on the hydrodynamic performance and energy conversion efficiency of an efficient wave energy converter using a simple conceptual design. The system is based on a mechanical device power take-off (PTO) so-called a bidirectional rotary motion converter (BRMC), which can absorb wave energy by converting bidirectional motion of ocean waves into one-way rotation of an electric generator. First, a prototype system is designed, fabricated and assembled in the Research Institute of Small & Medium Shipbuilding (RIMS). The tests are carried out under different conditions, such as wave profiles, the resistive load coefficients and supplementary masses. A wave simulator is controlled to make harmonic waves with different amplitudes and frequencies. Metal plates are added and fixed on the buoy as supplementary masses. Closed-loop torque control has been applied on the Magneto-Rheological (MR) brake to simulate the induced torque of an electric generator. Moreover, the rotary angle compared to vertical direction, is adjusted to investigate the influence of surge mode and heave mode combination on the absorption energy. The output power is calculated and compared with maximum theoretical absorbed power in heave mode to evaluate the efficiency of the prototype under different conditions. Finally, at optimum condition, the efficiency of the PTO system can reach 80.4% including frictional loss, and the capture width ratio is up to 41.6%.