Performance study and multi-objective optimization of 3D cylindrical oscillating water column wave energy converter: balancing efficiency and structural cost

Striking a balance between energy conversion efficiency and manufacturing costs is crucial for the successful commercialization of wave energy technologies. To achieve this goal, this study first develops a multi-objective optimization framework based on a three-dimensional computational fluid dynamics (CFD) model. This model is then integrated with a surrogate-based optimization algorithm to efficiently optimize the geometry of a cylindrical oscillating water column wave energy converter (OWC-WEC). This novel framework is designed to enhance energy conversion performance while minimizing computational expense. From the numerical results, it is known that the underwater external structure of the OWC device plays a critical role in energy conversion. Furthermore, the draft of the device significantly influences the optimal wave period for maximum power extraction. An increase in wall thickness impedes the ingress of water particles into the chamber and raises manufacturing costs. The opening ratio of the device affects the aerodynamic damping coefficient, which in turn governs the energy conversion efficiency. Under different sea states, optimal configurations tailored to each scenario can be conducted. The optimized design achieves an energy conversion efficiency more than 0.6, with an average efficiency improvement across the operational sea state range, and a maximum increase of 237.8% in specific power output (power per unit structural mass). The methodology provides valuable insights into the integrated hydrodynamic and structural optimization of OWC-WECs.