Fully nonlinear investigations on performance of an OWSC (oscillating wave surge converter) in 3D (three-dimensional) open water

The hydrodynamic behavior of a hinged Oscillating Wave Surge Converter (OWSC) device in open water, including motion response, extracted power and capture efficiency, is numerically investigated through a developed three-dimensional (3D) fully nonlinear higher-order boundary element method (HOBEM) model. In this time-domain mode, an image Green function is adopted in the whole circular domain with radiation condition at far field to avoid re-reflection from the lateral walls and resonance of the transverse standing waves which both occur in 3D numerical wave tank. The calculated surface elevation and the structural response are compared well with the existing measured and numerical results. It can be proved from present results that wave nonlinearity would change the flap's natural frequency and break the limit of highest possible efficiency 50%. An OWSC with thinner thickness and wider width becomes more efficient for extending the applicable extent of wave frequency for performance improvement. In addition, when the OWSC device is installed at the shallow water depth, the energy extraction can be magnified due to shoaling effect. The time series further reveal that the larger wave amplitude leads to the motion response dominated simultaneously by difference frequency, fundamental frequency and higher-order frequencies. (C) 2020 Elsevier Ltd. All rights reserved.