On energy transfer of parametric resonance for wave energy conversion

Parametric resonance has been observed, both numerically and experimentally, in various studies of wave energy converters (WECs). A large motion in heave induces a periodic variation in the metacentric height of a WEC body, and, consequently, causes a harmonic variation in pitch/roll restoring coefficients, which can parametrically excite the pitch/roll modes. Current studies have a specific focus to determine the occurrence conditions of parametric resonance, by detecting the boundaries between stable and unstable regions in the parameter space. In the literature, some studies aim to make use of parametric resonance for improving power capture. In contrast, some studies try to suppress the effect of parametric resonance, as it reduces power capture efficiency. However, how energy transfers from one mode to another is not fully understood. This study aims to analyse the energy transfer between heave and pitch/roll modes when parametric resonance occurs. A generic cylindrical point absorber is studied as a WEC floater to considering non-linear wave-structure interaction, including non-linear Froude-Krylov and viscous forces. A heave-pitch-roll three-degree-of-freedom model is derived for numerical study of the energy transfer between different operation modes.EWTEC 202