Abstract: Floating body design is the key to energy capture in an oscillating body wave energy capture system. The power output of floating body is often assumed as linear damping in hydrodynamic study. It is more suitable to adopt nonlinear output damping for the hydraulic wave energy conversion. For a heave body hydraulic conversion system, the non-linear dynamic model of the heave body under irregular waves and the non-linear hydraulic conversion system model are established. The influences of cylinder diameter and draft on the motion response of floating body, the dynamic performance and overall characters of hydraulic conversion system are investigated. As the cylinder diameter increases in a certain range, the peak values of irregular wave exciting force, hydraulic cylinder output force, floating body motion response, energy capture and power output all increase significantly, and the mean values of energy capture, capture efficiency, motor power output and speed increase nearly linearly. With the increase of draft in a certain range, the wave exciting force decreases linearly, and hydraulic cylinder output force, energy capture and capture efficiency slowly increase to the maximum then decrease gradually. The cylinder diameter and draft have little effect on hydraulic conversion efficiency. The research results provide a theoretical basis for floating body design of wave energy capture hydraulic system.

Key words: cylindrical floating body, wave energy capture, hydraulic conversion, parameter influence, system performance