Hydrodynamic performance of a pile-supported oscillating water column breakwater in front of a partially reflecting seawall

Abstract

Integrating wave energy devices with breakwaters can offer an innovative and sustainable approach by combining wave power extraction with wave attenuation. The performance of this integrated system in offshore areas is influenced by the unique characteristics of the coastline. In this paper, a semi-analytical solution was developed using the matching eigenfunction method for the oscillating water column device integrated into a pile-supported breakwater in front of a partially reflective seawall. The model was validated through the energy conservation law, the Haskind relationship, and experimental data. Detailed examinations were conducted on the effects of the seawall's reflection coefficients, the distance between the system and the seawall, the wall draft, and the chamber breadth on hydrodynamic performance. Results show that the presence of the seawall significantly influences hydrodynamic coefficients (hydrodynamic efficiency, reflection coefficient, the relative transmitted amplitude, etc.), accompanied by the piston and sloshing mode resonances inside the chamber and the confined area between the system and the seawall. Due to energy dissipated by a partially reflective seawall, the magnitude of those hydrodynamic coefficients is mitigated, together with the piston and sloshing mode resonances inside the air chamber. The cancellation of the sloshing mode resonance inside the confined area is observed for the smaller seawall's reflection coefficient. The maximum and minimum hydrodynamic efficiency occur when the system is arranged at the wave nodes and antinodes of the formed standing wave field. Lower wave reflection and better wave power extraction can be achieved by properly adjusting the chamber drafts and breadths.