Hydrodynamic characteristics of an oscillating water column caisson array mounted on the stepped bottom

This paper presents a semi-analytical solution based on linear potential flow theory for the hydrodynamic performance of an oscillating water column (OWC) caisson array deployed on a stepped seabed, where the array consists of multiple identical OWC units placed side by side with no gap along the alongshore direction. The solution employs a periodic boundary condition in the along-shore direction. The solution is validated by the energy conservation law, the Haskind relationship, and comparison with published computational fluid dynamics results. The geometric parameters used in the parametric study are inspired by the relative proportions of the Mutriku plant. Quantitative results from this inviscid model reveal that hydrodynamic efficiency reaches nearly 100% due to step resonance, representing a theoretical upper bound. Null efficiency occurs when the along-shore length of the chamber equals half the incident wavelength (kl = 0.5π), due to the transverse chamber sloshing mode. The bathymetrically trapped mode, arising from the coupling between the evanescent and propagating modes, appears between klj=−1cr2 and klj=−1cr1. This resonance is essentially a trapped mode related to edge waves and Rayleigh–Bloch waves, producing near-zero efficiency and abrupt changes in both transverse and longitudinal forces. These findings provide guidance for the preliminary design and performance prediction of OWC caisson arrays in offshore areas with variable bathymetry.