Three Degree of Freedom Wave Energy Converter Design for Resonant Motion

As multiple-degree-of-freedom (3-DOF) wave energy converters (WECs) have demonstrated the ability to produce more power than single-degree-of-freedom devices, the challenge of designing buoys for efficient energy harvesting has increased in complexity. In this paper, a cylindrical WEC is designed to naturally resonate in surge, pitch, and heave modes at a specific target frequency of 0.2 Hz. By utilizing a penalty-based optimization method to balance buoyancy requirements with natural resonance, the design achieves minimal control force input, thereby reducing fluctuations in energy output and local energy storage requirements. The performance is evaluated under irregular sea states using a Bretschneider spectrum. Results indicate that a buoy optimized to naturally resonate at the modal frequency of a sea state provides consistent power with significantly reduced reactive power demand compared to non-optimized designs.