Numerical Simulation of the Effect of Buoy Geometries on PTO of Wave Energy Converters

Abstract

Moving water has one of the highest energy densities, yet a major untapped and underutilized area of energy production is wave energy. With the recent interest in the Blue Economy, this is about to change. Point Wave Energy Converter (PWEC) absorbs the wave energy at a single point and is characterized by the buoy surface component and a longer subsurface component that is attached to the seabed. The motion of the top buoy is used to pump fluid or drive a linear generator, which in turn provides power. This paper numerically investigates different shaped surface buoys, with a focus on the power-generating ability of the system, for a single point WEC using a non-linear free surface approximation. Three-dimensional simulations of the buoys in various sea states were modeled in OpenFOAM using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with Finite Volume Method (FVM). The dynamic mesh module was integrated with the two-phase solver, and the mechanical system of the WEC was modeled with a forced oscillator mechanism. By studying the displacements, frequency responses, and design parameters, the optimal buoy shape for maximizing energy output was determined. Further, the guidance regarding the effect of changes in the geometry, represented by the length to diameter ratio of the shape, is discussed. The results showed that the spheroid buoy shape with a low length to diameter ratio is a good candidate shape to extract wave energy since it has a large waterplane area.