<p>This study examines the impact of seabed undulations, shaped as semi-circular and triangular patches, on the hydrodynamic performance of an oscillating water column (OWC) wave energy converter. The undulations are placed at a finite distance from the OWC to create gap resonance under the influence of incident wave-currents. The seabed patch is assumed to be impermeable for most test conditions, and permeability is added to mimic natural sandbars in front of the OWC. The multi-domain boundary element method (MDBEM) is used to solve the boundary value problem, with results validated against experimental and numerical data. The study investigates the influence of current velocity (via Froude number), number of undulations, lip-wall spacing, chamber spacing, lip-wall draft and inclination, wave angle, wavelength, and undulation geometry on key hydrodynamic parameters. These include OWC efficiency, radiation susceptance, conductance, and wall forces. Effects are analyzed across different relative water depths and clear spacing. The influence of semi-circular and triangular undulations, porosity, and undulation count is studied using surface plots. Comparative analysis shows that semi-circular and trapezoidal seabed patches improve OWC efficiency more than a plane seabed. Wave-currents further enhance energy capture, making these configurations more effective for wave energy conversion.</p>