OPTIMAL HEAVE MOTION OF SOME AXISYMMETRICAL WAVE ENERGY DEVICES IN SINUSOIDAL WAVES

We present a mathematical model of the transient motion of a floating body wave energy device, including memory and an impulsive term. The m emory is calculated from the damping coefficients in the frequency dom ain, and forms the kernel of an integral which is a component of the e quation of motion to be solved numerically. The impulsive term is calc ulated from the added mass. Convergence of both memory and impulsive t erms in water of finite depth is considered. It is shown that the (mor e general) transient memory model agrees with the usual added mass and damping model for the large time behaviour of a body with linear exte rnal constraints (power take-off), but that the full memory model is e ssential for studying either transient motion or motion with non-linea r constraints. An examination of the equation of motion in the time do main suggests the possibility of implementing non-linear strategies su ch as latching to improve the efficiency of the system. Results are pr esented for a heaving hemisphere and two different truncated vertical circular cylinders (with geometries given by the Swedish and Danish he aving buoy devices). (C) 1997 Elsevier Science Ltd.