Basic Research in Resonance Characteristics of a Water Column in the Oscillating Water Column Type Wave Energy Converter by Free Decay Test

Abstract Wave energy, a renewable resource, is gaining attention for its abundance and high energy density. Floating oscillating water column-type wave energy converters (OWC-WECs) are important, combining the simplicity and low maintenance of OWC-WECs with the flexibility and environmental benefits of floating structures. The natural period of the water column in OWC-WECs is typically calculated based on air chamber dimensions, with more advanced estimations using an effective length parameter. However, Power take off (PTO)-damping, a key factor for power generation, is neglected. PTO-damping influences the damping ratio of water column motion and alters the resonant period at which the water column responds to waves. To develop higher-performance OWC-WECs, understanding the water column motion, including PTO damping, is crucial. Computational fluid dynamics (CFD) is effective for analyzing this motion, and while grid-based CFD has been used in OWC-WEC optimization, it must consider survivability in rough conditions and robustness against nonlinear phenomena. This study employed a moving particle simulation (MPS) method to analyze the performance of a floating OWC-WEC. The MPS method, compared to mesh-based CFD, captures free surface dynamics and handles complex fluid-solid interactions. The authors conducted a free decay test and water tank experiment for two OWC shapes—bottom and side openings—and analyzed the natural period, damping ratio, and added mass through numerical simulations.