Viscous effects on the performance of wave energy converters in shallow water

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 in real wave environments around the world. Mathematical modelling has been used extensively to investigate the performance of these devices. Linear theory has been used successfully to study the performance of various WEC designs but assume inviscid and irrotational conditions allowing for potential flow solutions thus limiting their applicability to deep or intermediate water situations.

The goal of this study is to analyse the forcing and wave fields surrounding a single WEC in the transition from intermediate to shallow water depths. The focus is placed on a submerged sphere oscillating both in heave and surge. The diffracted and radiated waves on the free surface are modelled using a viscous, non-linear volume of fluid numerical wave tank with the commercial software package StarCCM+ and are analyzed against experimental results. This study follows the linear solution approach by solving the diffracted and radiated wave fields separately.

The analysis of the shallow water non-linear effects will focus on the individual fields. The hydrodynamic forces on the sphere and the variations to the diffracted and radiated waves are analyzed, highlighting the main variations caused by the shallow wave non-linear waves. This work will offer an indication of expected WEC performance in shallow water and serve are a benchmark to progress to WEC array studies.