Impact of wave focusing and transverse sloshing on the wave energy harvesting of an oscillating water column (OWC) in a wave flume

Focusing wave energy on an oscillatory wave column (OWC) is an effective way to enhance its energy harvesting efficiency, which is quantified by the capture width ratio (CWR). A properly designed rectangular OWC can achieve a maximum CWR greater than 100% because of its inherent ability of wave focusing. For an infinite row of OWC devices under perpendicularly incident waves, the hydrodynamic efficiency of each OWC device is affected by two factors: wave focusing and possible transverse sloshing. Due to symmetry, this configuration is equivalent to one OWC device within a wave flume. This study uses numerical simulations to investigate the impact of wave focusing and transverse sloshing on the performance of an OWC device in a wave flume. The peak CWR is found to decrease with a decrease in the flume width. It reduces from 1.402 to 0.946 as the flume-width-to-OWC-width ratio decreases from 5 to 1.05. Through wave ray visualization, this paper found that the fundamental mechanism of transverse sloshing that causes minimum values of CWR is the multiple reflection of the waves between the flume side wall and the centre line of the OWC. • Mechanisms of wave focusing in front of a rectangular OWC device is discovered. • OWC Efficiency of a rectangular OWC reduces with the reduction of the flume width. • Mechanism of transverse sloshing is multiple reflection in the trans-flume direction.