Tidal Currents Effect on the Performance of a Heaving Point Absorber

Point absorbers are the most common type of wave energy converters. This study assesses the vertical motion of a point absorber, which may be simplified as a mass-spring damper system. While some studies have previously investigated the impact of tidal currents on wave energy resources, this research is focused on the impact of tidal currents on the performance of a point absorber. To evaluate how a point absorber is affected by wave-current interaction, a semi-analytical method was developed based on the linear wave theory following the conservation of wave action. Based on this formulation, the hydrodynamic forces on the point absorber were calculated in the presence of currents. For the specific device under consideration, it was shown that a tidal current with a peak of -0.75 m/s could increase the energy extraction by 54% when comparing an opposing current to no current condition. The energy extraction could decrease by 30% when comparing a following current of 0.75 m/s and no current case. Although this study finds an increase in extracted energy for a point absorber due to wave-current interactions, there are issues that require further investigation. Impacts of currents on mooring were not explored in this study and may lead to differences in extracted energy. Furthermore, a very strong tidal current may cause wave breaking or block wave energy propagation which is not considered in linear wave theory.