Design and Numerical Performance Assessment of a Variable-Geometry Two-Body Wave Energy Converter

Abstract

Wave energy converters (WECs) offer a promising pathway toward diversifying renewable energy portfolios, particularly for coastal and island regions with persistent wave climates. Among existing architectures, two-body WECs are attractive due to their ability to exploit relative motion and multiple degrees of freedom for enhanced energy capture. However, conventional designs often suffer from narrow-band performance and limited adaptability to varying sea states. The objective of this study is to design, numerical modelling, and performance evaluation of a two-body point absorber wave energy converter incorporating a mechanically realizable variable-geometry mechanism. The proposed system consists of a floating body and a submerged body coupled through a direct-drive linear power take-off (PTO), with adjustable float positioning enabled by an ACME power screw and worm-gear actuation. The variable geometry allows controlled modification of hydrostatic stability, restoring moments, and resonance characteristics. Hydrodynamic coefficients were computed using linear boundary element methods in ANSYS AQWA and integrated into WEC-Sim for time-domain simulations under both regular and irregular wave conditions. Structural integrity and fatigue performance were assessed using finite element analysis to ensure survivability under representative operational and extreme sea states. Simulation results demonstrate that float spatial configuration has a pronounced influence on hydrostatic stability, motion response, resonance behaviour, and power absorption efficiency. Among the tested configurations, the intermediate (middle) geometry consistently achieved the most favourable balance between motion amplification and stability, resulting in superior energy capture potential across a wide range of wave periods and heights. The highest configuration provided increased structural safety and reduced fatigue loading, while the lowest configuration exhibited reduced dynamic efficiency due to adverse righting moment characteristics. Overall, the findings confirm that mechanically feasible variable-geometry integration significantly enhances the adaptability and performance of two-body WECs. The proposed design offers a scalable and robust solution for improving wave energy conversion efficiency under realistic, variable sea-state conditions, supporting the advancement of practical and deployable wave energy technologies.