Non-linear CFD modelling of a submerged sphere wave energy converter

The use of wave energy converters (WECs) as a renewable source of energy is quickly becoming a reality with many prototype designs currently being tested at both model and full scale. Analytical and numerical modelling has been used extensively to predict the performance of these devices using linear, inviscid and irrotational theory as a basis. This work applies a non-linear, viscous volume of fluid RANS model to simulate the diffraction and radiation problems for a single heaving submerged spherical WEC. Two amplitudes of the incident wave and sphere oscillation are considered for three different frequencies. The amplitudes are chosen to correspond to both linear and non-linear wave forms. The results of the model are compared against those of a linear FEM based model with good agreement at small amplitudes. The hydrodynamic coefficients, considered constant under linear theory, are here found to be amplitude dependent as the oscillations become non-linear. Other non-linear effects to surface forces and fluid motions on and near the submerged sphere are also presented and discussed.