Abstract
This study develops and investigates motion control of a two-body point absorber wave energy converter (WEC) to allow for docking and recharge of an unmanned underwater vehicle (UUV). It addresses the conflicting requirements between power-mode operation, which favors large motions for energy extraction, and docking-mode operation, which requires minimal dock motion for UUV docking compatibility. Four control modes are considered: power mode (PM), passive docking mode (DM) with zero PTO damping, and two active strategies: velocity-proportional (VP) and linear quadratic (LQ) control. Results show that PM produces large dock heave velocities on the order of 0.6–1.4 m/s, which are unfavorable for docking, while DM reduces motion but remains insufficient, particularly in moderate to rough sea states. VP control achieves superior motion regulation, reducing dock velocities to below 0.03 m/s, but requires higher reactive power, resulting in negative net power. In contrast, LQ control reduces velocities to 0.07–0.28 m/s while maintaining positive net power, corresponding to a 70%–85% reduction relative to power-mode operation. Performance is fundamentally constrained by the inherent heave-only WEC power-take-off (PTO) actuation, which limits the ability to control surge and pitch, and motivates system-level improvements in controllability. The results establish docking-mode control as a distinct operational framework and provide guidance for integrated WEC–UUV system and control design.