Influence of distinct bottom geometries on the hydrodynamic performance of an OWC device

The hydrodynamic performance of a shore-fixed oscillating water column (OWC) device in the presence of convex, concave and sloped step-type bottom profiles is investigated. The present study employs two different numerical approaches viz. Boundary Element Method (BEM) and Computational Fluid Dynamics (CFD) to carry out the task. BEM computations in a two-dimensional (2D) Cartesian coordinate system using linear water wave theory are compared with CFD simulations using a numerical wave tank (NWT) built with a multiphase volume of fluid (VOF) approach . Hydrodynamic efficiency analysis was carried out for different curved bottom geometries. In both models, the resonating behaviour and the performance curve follow similar trends for the device. Both models agree upon the fact that the performance of the convex bottom is on the higher side for lower incident wave frequencies. The flow characteristics and the free surface elevations are investigated inside and around the OWC chamber. It was observed that the pattern of wave energy capture is distinct for frequencies lower and higher than the optimal frequency for various bottom curvatures. Also, the differences in efficiency for various bottom geometries compared with the 'flat bottom' case are more prominent for a lower front wall depth of 0.25 m. This study should apply to wave energy converter devices installed nearshore, where the presence of bottom curvature influences the hydrodynamic behaviour and hence the capture efficiency.