Hydrodynamic performance of a periodic array of flap-type devices installed on the stepped bottom topography in the front of the coastal wall

Abstract

Harnessing wave energy stands as a promising method to mitigate carbon dioxide emissions and address the global energy shortage. The strategic placement of wave energy converters (WECs) in offshore areas is contingent upon the distinctive features of the coastline and the topographical layout. This study is dedicated to scrutinizing the hydrodynamic characteristics and the wave energy absorption of a periodic array of flap-type WECs situated on a stepped bottom topography, strategically positioned in front of a straight coast. The coastline is modeled as a fully reflecting vertical wall. To analyze the oblique wave interaction with this system, we have developed a semi-analytical solution grounded in the linear potential flow theory. We evaluated key performance metrics, including hydrodynamic efficiency, reflection coefficient, wave excitation torque, added inertia torque, and radiation damping. Case studies were conducted to assess the impacts of varying parameters, such as the distance between the flap and the wall, the wave depth above the step, the incident angle, and the step length on the hydrodynamic performance of the current system. The results underscore the substantial influence of the distance between the flap and the coastal wall on wave power efficiency. The trigger condition's frequency downshift, indicative of the standing wave field between the flap and the coastal wall, is observed with a reduction in the wave depth above the step, in contrast to scenarios without the step. In addition, wave resonance above the stepped bottom topography amplifies wave power extraction, albeit with the caveat of a diminished hydrodynamic efficiency due to the presence of Rayleigh–Bloch waves.