Numerical investigation of a pile-supported oscillating water column breakwater under oblique wave incidence and variable bathymetry

This study carries out a boundary element analysis to numerically investigate the hydrodynamic performance of a pile-supported oscillating water column breakwater wave energy converter subjected to obliquely incident waves, within the framework of linear potential flow theory. A bottom undulation effect, created by varying water depths on the lee and seaward sides, is adopted as an effective strategy to enhance wave power extraction under obliquely incident waves. Key hydrodynamic parameters, including optimal efficiency, wave reflection, transmission, wave loads, damping characteristics, diffraction flux, and optimal power exerted, are systematically investigated. Besides, the key hydrodynamic parameters are formulated and validated against the newly derived Haskind relation for obliquely incident waves. The findings reveal that an optimal chamber width ratio (b/h1=0.15) and front wall submergence (a1/h1=0.15), combined with a rear wall draft of a2/h1=0.40 maximize the energy capture while maintaining structural balance. Additionally, moderate oblique wave angles (30° and 45°) significantly enhance resonance and power output. Furthermore, a lower water depth ratio (h2/h1=0.55) effectively broadens resonance bandwidth and minimizes wave transmission, improving both efficiency and resilience. The study also demonstrates that seabed non-uniformity and concave bottom profiles can significantly enhance energy extraction compared to a conventional stepped seabed by amplifying the wave propulsion of the incident wave within the water column.