Three-stage optimization framework for improving the energy capture of a heaving point absorber wave energy converter through buoy geometry and PTO control

To improve the energy capture of point absorber wave energy converters (WECs) under practical engineering constraints, a three-stage optimization framework integrating buoy geometry and power take-off (PTO) control is proposed. Stage I optimizes the principal dimensions of the buoy through diameter-to-draft ratio (DDR) analysis using a capture-width-based metric. Stage II refines the lower-hull geometry by introducing a parameterized bulbous-bottom configuration characterized by fillet height and protrusion width. Stage III comparatively assesses PTO control strategies to improve phase alignment and energy conversion. Combined frequency-domain and time-domain analyses identify an optimal DDR of 2.8 as a compromise between hydrodynamic efficiency and structural scale, and show that the h1w3 bulbous-bottom configuration delivers the best geometric performance. Among the PTO strategies, reactive control raises the capture width ratio from 0.264 to 0.380 in regular waves and preserves this gain across JONSWAP irregular seas, with the benefit further amplified in long-period conditions, although its implementation requires negative stiffness and bidirectional power flow. Numerical simulations and 1:5 scale model experiments verify the effectiveness of the framework, providing a systematic, engineering-oriented design pathway for point absorber WECs.