Gap Resonance Effects on the Performance of Oscillating Water Column Under the Influence of Wave Currents

Abstract The efficiency of an oscillating water column (OWC) device is numerically evaluated in the presence of inverted trapezoidal breakwaters (ITBs) under the influence of ocean wave currents, using the multi-domain boundary element method. The gap resonance effects on the performance of the OWC are examined, considering variations in energy efficiency, radiation susceptance, conductance, and force exerted on the wall, under the framework of the small-amplitude wave theory. The impermeable ITBs are placed far away from the OWC device and are assumed to maintain a certain gap to enhance the fluid resonance. The effect of the current, chamber spacing, lip-wall draft, wall inclination, angle of attack, and ITB height is evaluated on the variation of hydrodynamic coefficients for impermeable ITBs. Thereafter, the integrity of the ITB shape in creating harmonic resonance is tested by comparing it with other conventional shapes, such as rectangular, trapezoidal, and triangular breakwaters. The component of porosity is introduced for the multiple ITBs to check the development of the Bragg resonance and its effects on the variation of OWC performance. The harmonic oscillations of engineering coefficients required and non-required resonant effects are highlighted, and their significance on the OWC performance is presented. Efficiency is observed to approach maximum when the ITBs are present. Replacing the ITBs with other structures significantly reduced efficiency at a specific frequency due to altered resonance. The increment of the angle of contact weakens the Bragg resonance by ITBs. Overall, a triple ITBs with seaside lip-wall is suggested to extract higher wave energy using an OWC device.