Nonlinear stiffness enhancement of submerged wave energy device in high fidelity model

Abstract

A three degree of freedom submerged wave energy converter with a nonlinear stiffness mechanism was modelled using both linear and nonlinear hydrodynamics. The linear hydrodynamics scenario used linear potential flow methods to predict the fluid–structure interaction, while the nonlinear hydrodynamic scenario use computational fluid dynamics (OpenFOAM). The potential energy of the nonlinear stiffness mechanism was varied relative to the potential energy of the incident wave. The wave energy converter was excited using regular and irregular waves. The nonlinear stiffness scenarios were compared to scenarios with optimised linear control parameters. When compared to optimal conditions, models using linear hydrodynamics to emulate both regular and irregular waves showed no improvement in power generation. In the regular wave nonlinear hydrodynamic scenarios, the nonlinear stiffness showed inconsistent improvements to power production and significant detuning at different levels of nonlinearity. The irregular wave scenario using nonlinear hydrodynamic methods demonstrated a small improvement compared to optimised linear control parameters when the nonlinear stiffness potential energy peak was less than half the potential energy of the incident wave. The nonlinear stiffness improved the robustness of the wave energy converter, and was an effective method for detuning the system, depending on the degree of nonlinearity.