Hydrodynamic Performance of an Oil Rig–Oscillating Water Column in Low Wave Climate

The oscillating water column (OWC) device is one of the most promising ocean wave energy extraction technologies. Most OWC studies focus on high-wave density areas, but there is limited research in low-wave density regions. This study evaluates the hydrodynamic efficiency of a 1:40 scale offshore OWC model in low-wave climates. Experiments were conducted using five different relative gaps (i/d) between the model and horizontal bottom plates, each with three distinct shapes (cone-shaped, circular-shaped, and flat), across seven wave periods in a wave flume. Hydrodynamic performance was measured through the amplification factor (Ai), which is defined as the ratio of water surface elevation inside the chamber to the incident wave height. Higher amplification factors indicate better efficiency, and comparisons were made between OWCs with different bottom plate shapes and configurations with and without a bottom plate. Among the shapes, the circular bottom plate achieved the highest Ai across a wide range of relative widths (B/L), peaking at B/L = 0.04, followed by the cone-shaped and flat plates. The performance peaked at a relative gap of i/d = 0.4 (0.25 m), beyond which efficiency significantly decreased. The absence of a bottom plate increased efficiency by up to 50%, particularly in low-energy wave conditions. Additionally, the presence of bottom plates reduced Ai due to the shoaling effect and seabed interactions under shallow water conditions (d/L < 0.18), limiting wave energy capture. These findings highlight the importance of optimising bottom plate design and relative gaps to enhance OWC efficiency in low-wave climates, contributing to the broader advancement of wave energy technology in similar environmental conditions.