Irregular deep ocean wave energy attenuation using a cycloidal wave energy converter

Abstract The performance of a lift based wave energy converter in unidirectional irregular deep ocean waves is investigated. The energy converter consists of two hydrofoils attached parallel to a horizontal main shaft at a radius. The main shaft is aligned parallel to the wave crests and submerged at a fixed depth. The local flow field induced by the incident wave will cause the hydrofoils to rotate about the main shaft. The orientation of each hydrofoil is adjusted to produce the desired level of bound circulation. The energy converter and incident wave field are modeled using potential flow theory. The wave field is assumed to be long-crested and the hydrofoil span infinitely long, thereby the resulting flow field is two-dimensional. Each hydrofoil is modeled as a point vortex moving under a free surface. The irregular ocean wave is modeled by linear superposition of a finite number of regular wave components. The amplitude and frequency of each component is determined based on a Bretschneider spectrum. The hydrofoil position and bound circulation are controlled using a sensor located up-wave of the device and wave state estimator. The results demonstrate the converter’s ability to effectively extract energy from multiple wave components simultaneously. Inviscid hydrodynamic efficiencies for incident wave fields consisting of 7 and 10 regular wave components were 85% and 77%, respectively.