In order to design a floating OWC (Oscillating Water Column)-type wave energy converter such as Backward Bent Duct Buoy (BBDB) optimally, it is necessary to develop a numerical method to make clear an optimal hull shape which maximizes the generating electrical energy.

In this paper, a two-dimensional numerical method in time domain to estimate the primary conversion efficiency of a floating OWC-type wave energy converter with arbitrary cross section is proposed. The fluid motion in water waves is calculated by using vortex method which can consider viscosity of the fluid, vortex generation from the floating body surface and diffusion of the vortex into the fluid. For air flow in air chamber, equations of state, conservation of mass and energy with the assumption of air being the perfect gas are used. From these equations, motions of floating body, air pressure and free surface elevation in air chamber and primary conversion efficiency etc. are calculated. Wave tank tests are also carried out for BBDB in regular waves. Numerical results are compared with experimental results.