Array buoys with nonlinear stiffness enhance low-frequency wave attenuation and energy capture

Abstract

Extraction of energy and elimination of ocean waves at low frequencies are challenges facing current wave energy devices. A recent idea based on reducing the equivalent stiffness has been applied to such devices for low-frequency wave attenuation and energy capture. This study investigates a model of an array of buoys with an additional nonlinear stiffness mechanism to this end. The problems of hydrodynamic interaction between multiple floating bodies and interactions among nonlinear wave structures are solved by a semi-analytical method that combines the eigenfunction matching expansion method with the multi-harmonic balance method. The physical mechanism of the proposed nonlinear system of multiple buoys was explored, and it was found to deliver good performance in terms of power capture and wave elimination due to its “phase control” feature. Bragg resonance occurred in the arrayed buoys, which was not conducive to hydrodynamic efficiency. The properties of the multi-buoy system were evaluated, and it was found to be superior to a single buoy of equal volume. The results of this study indicate that an attached mechanism with nonlinear stiffness can be beneficial both for exploiting wave energy and reducing transmitted waves.