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An energy focusing submerged wave energy device with active control

Recent years have seen a considerable resurgence of interest in ocean wave energy conversion systems world wide. Active control of device dynamics can enable smaller, more cost-effective, devices to absorb greater power from the available wave resource. In this poster, we discuss wave energy conversion based on an actively controlled system of dynamically coupled submerged bodies. It is known that submerged, near-surface, stationary circular discs can cause considerable wave-field focusing in their immediate neighborhood. In the three-body axisymmetric device considered here, the vertical oscillations of the bottom disc are controlled to hold the top disc nearly stationary over a wide range of incident wave frequencies. This enables the device to focus the incident wave field over a range of frequencies. We examine here active control using feedback of the absolute position and acceleration of the bottom disc. The oscillations of the middle disc, in response to the focused wave field, are utilized for energy conversion by hydraulic rams or linear generators supported from the top disc. While time domain control of the middle disc for optimal conversion will require wave elevation/oscillation prediction, frequency-domain control and tuning may be accomplished without prediction. Approximate analysis results for capture efficiency under frequency-domain control are discussed.