Investigation of stepped bottom effects on a multi-float WEC-breakwater system using OpenFOAM

This study systematically investigates the hydrodynamic performance of a hybrid Wave Energy Converter (WEC)-breakwater system with a stepped bottom. The open-source Computational Fluid Dynamics (CFD) model, OpenFOAM, is validated with experiments of the hybrid system. The validated model is then used to investigate the influence of submerged step dimensions on the hydrodynamic characteristics of the system, including wave reflection and transmission coefficients, and wave energy conversion efficiency. The impact of Power Take-Off (PTO) damping and wave nonlinearity on its performance as a WEC and breakwater are also examined. It was found that the submerged step effectively reduces wave transmission and enhances energy conversion efficiency. When the step length in front of floats is an integral multiple of a quarter wavelength, L/4, resonance occurs, which amplifies the float motion. Increased step height reduces wave transmission and boosts energy conversion, but raises construction costs. Notably, vortex generation at the float and step dissipates wave energy, therefore, significantly weaken wave transmission. While an optimal damping coefficient exists for energy conversion in a linear PTO system, employing a larger damping coefficient does not significantly reduce energy conversion efficiency but effectively enhance wave attenuation. This study provides insights for design of multi-float WEC-breakwater systems and its enhanced wave attenuation and energy extraction through a stepped bottom.