Effect of the Incident Wave Angle on the Hydrodynamic Performance of a Land-Based OWC Device

Abstract

AbstractThe majority of experiments on fixed Oscillating Water Column (OWC) systems assume that water waves impact perpendicularly on the front wall of the device. However, this seldom occurs in practice due to wave transformation, which occurs when waves interact with shifting bottom profiles resulting in wave reflection, refraction and shoaling. The wave angle of incidence is of paramount relevance because it can alter the performance of the OWC device, particularly the natural period at which the device resonates. Therefore, this work investigates the interaction of directional waves with a fixed land-based OWC device. Theoretical and experimental techniques to study the effect of wave direction on the device hydrodynamic performance are described. The mathematical problem for the theoretical approaches is formulated using two-dimensional linear wave theory. The conventional eigenfunction expansion method (EEM) and the Boundary Element Method (BEM) are used to solve the governing equation together with the boundary conditions. Then, a series of experimental tests under regular wave conditions were carried out in a directional wave basin to compare and validate the theoretical results. The effects of wave angle of incidence on hydrodynamic efficiency are examined. Analytical and numerical predictions of the resonance frequency for different wave angles of incidence were found to be in good agreement when compared with experimental tests. Findings reveal that the resonant frequency of the system increases exponentially when the incident wave angle increases, a trend that is more visible for wave angles beyond 15\(^\circ \). Results indicate that analytical and numerical techniques can be employed as design tools to estimate the natural frequency of the system when it interacts with oblique regular waves.KeywordsOscillating water columnOblique wavesHydrodynamic efficiencyResonant frequencyWave energy