The influence of mass optimization on the energy absorption efficiency of a submerged body of a two-body wave energy converter

A procedure is proposed to minimise the submerged body's total mass in a two-body wave energy converter. To this end, three modelling steps are considered, with two default values: the absorber buoy geometry and the wave characteristics. The total mass, which includes both the submerged body's mass and its hydrodynamic added mass, is calculated based on the absorber buoy's specifications and its wave-energy absorption bandwidth. In the first step, the submerged body's optimal mass is achieved 66% of the buoy's mass. The second step is the effect of the body's shape on the model's efficiency. With an optimal mass and proper shape for the submerged body, the maximum power is absorbed, about 62% more than the single-body power, in the resonance region. Moreover, the modelling method establishes identical conditions for comparing the performance of multiple bodies during energy absorption. It was found that two important criteria for the body's shape, which are the ratio of its hydrodynamic coefficients to the wave period, significantly affect the model's efficiency. The results show that higher efficiencies are achieved when a geometrically suitable body substantially reduces the added mass and radiation damping of the model's buoy relative to its free oscillation.