Evaluation of oscillating water column efficiency in the presence of multiple bottom-standing breakwaters under oblique waves

Abstract

This study proposed an array of bottom-standing breakwaters (BSBs) in the presence of an oscillating water column (OWC) for a better understanding of physical mechanisms, under the framework of a linearized potential flow theory. The free water regions are provided between the multiple BSBs to utilize the gap resonance for energy extraction by OWC. The multi-domain boundary element method is adopted to conduct the parametric study, and the validation of the proposed model is presented. The effect of BSB physical properties, OWC, and incident wave properties are reported on the variation of OWC efficiency, radiation susceptance, conductance, force on the wall, and wave reflection by BSBs against the relative wave frequency and water depth. A comparative study on the variation of coefficients is presented between three types of BSB and flat seabed. The higher number of BSBs enhances the intensity of harmonics and subharmonics of coefficients and strengthens the harmonic trough of efficiency. The Bragg reflection by multiple BSBs diminishes the efficiency of OWC for particular wavelength, and the Bragg peak is suppressed by adopting the permeable property for BSBs. The enlargement of OWC efficiency toward the higher frequencies is observed with an increase in BSB height, width, and chamber length. This study suggests a pair of BSBs with a chamber length equal to water depth for optimal efficiency. Overall, the seaside inclined lip-wall, moderate chamber length, and double BSBs are recommended to diminish the Bragg peak (nearly 18%) and extract the maximum renewable energy for a wider frequency, from the OWC device against the incident waves.