Robust performance improvement of a raft-type wave energy converter using a nonlinear stiffness mechanism

In order to enhance the capture efficiency and broaden the bandwidth, a novel rotation Power Take-off with nonlinear stiffness is proposed and applied to a traditional raft-type wave energy converter (WEC). Refer to Cummins' equation, the governing equations of motion for a WEC with nonlinear stiffness in the time domain is established based on linear hydrodynamic model. The harmonic balance method is employed to solve the set of nonlinear dynamic equations. The characteristics of the wave absorption in regular and irregular waves are analyzed by using numerical simulations. The effects of the systematic parameters and wave conditions on wave energy capture efficiency are analyzed. The numerical results show that the nonlinear stiffness mechanism with appropriate parameters can enhance capture efficiency and broaden frequency bandwidth of the energy capture. Robust performance improvement without complex nonlinear phenomena of jumping and multiple solutions is revealed by using the analytical solutions. The nonlinear stiffness mechanism can provide a role of phase control for the raft-type WEC.