Floating wave energy converters (WECs) are installed at locations with high wave energy and in relatively shallow water where wave nonlinearity is amplified. As a result, wave impact loads constitute a major design consideration for wave energy converters and the violent impact of an extreme wave onto a wave energy converter can be the criterion that determines a number of design parameters. Numerical simulation of the coupled dynamic response of WEC and mooring in storm conditions and under extreme wave loading remains a complex and difficult problem. Nevertheless, quantitative understanding of the wave impact is very important to the efficient performance and long time survivability of a wave energy converter.
A new fully nonlinear CFD technique is developed to assess the wave impacts and dynamic response on wave energy converters. Wave breaking and overtopping occur under extreme wave loading on offshore WECs. Both the water and air that may be entrained when a wave breaks or overtops a structure should be modelled, and the interface between them defined with a high resolution free surface capturing technique. In this work, a Navier-Stokes equation model is used to simulate the hydrodynamics. A level set method with the global mass correction is developed to study wave breaking and overtopping, and the immersed boundary method is employed to capture the extreme wave load- ing on offshore WECs.
Calculations have been made for the entry and exit of a cylinder, in which the hydrodynamic force on the cylinder during the first stage of the impact is obtained. The slamming coefficients of the cylinder entry with different entry velocities are calculated and agree well with experimental results. This problem is of importance in the design of various floating structures that experience worst case loading.