FREQUENCY AND TIME-DOMAIN MODELS FOR A TWO-BODY WAVE POWER DEVICE THAT EXTRACTS ENERGY FROM SEA WAVES BY RELATIVE PITCH MOTION

ABSTRACT In this paper analytical and numerical tools are used to describe the behaviour of a new wave power device. This device extracts energy from sea waves by relative pitch motion between their two independent parts. Frequency-domain analysis is carried out assuming that its hydrodynamic performance and its power take-off equipment behaviour may be considered linear. For regular waves optimal mechanical damping coefficients are computed assuming restrictions to hold for relative pitch motion between the two device parts. Useful power, capture length as well as rotations and displacements are computed. Time-domain analysis is necessary if one needs to compute the device's performance under more realistic operational conditions. In order to get device's variables trajectories for irregular sea conditions, a time-domain approach is adopted since the hydraulic power take-off equipment exhibits a non-linear behaviour. Results are obtained for irregular waves, i.e. for different sea states, and thus trajectories for several device variables are presented. Power available to the hydraulic machine is computed and presented