Pseudo-nonlinear hydrodynamic coefficients for modelling point absorber wave energy converters

Abstract

This study presents dynamic simulation results of two point absorber wave energy converters comparing between linear, pseudo-nonlinear, and CFD models. When modelling wave energy converters, linear assumptions are commonly used to simplify calculations. One such assumption is that the hydrody- namic parameters do not change with pose. This study proposes the inclusion of position and orientation dependence in force estimation, specifically the hydrodynamic terms. A comparison between linear, the proposed pseudo-nonlinear, and CFD models show the effect of the linear assumption for cylindrical and spherical submerged buoys in three degrees of freedom, subject to regular waves. For the case of strong nonlinear hydrodynamic coupling between degrees of freedom, the linear and pseudo- nonlinear models are compared with published literature trends. Accounting for pose dependence of hydrodynamic forces, drag forces, and infinite frequency inertial effects showed trends closer to CFD results but with generally higher motion amplitudes. Significant differences in results for the cylinder are due to the presence of near-surface nonlinear effects that are not captured using linear potential flow solvers. Furthermore, a second order effect was observed in the results, suggesting the proposed method may be well suited to model sufficiently submerged buoys.