Hydrodynamic Considerations in Near-Optimal Control of a Small Wave Energy Converter for Ocean Measurement Applications

This paper investigates the use of wave energy to power long-term ocean sensing systems. The device examined here consists of an oceanographic buoy and a shallow-submerged reaction frame that may carry a science instrument. Power conversion is from the relative heave oscillation between the two bodies. The oscillation is controlled on a wave-by-wave basis using near-optimal feedforward control, which requires up-wave surface elevation measurement and deterministic prediction at the device location. This paper presents the dynamic formulation used to evaluate the near-optimal, wave-by-wave control forces in the time domain. Also examined are reaction-frame geometries for their impact on overall power capture through favorable hydrodynamic interactions. Performance is evaluated in a range of wave conditions (from most to least favorable for conversion) sampled over a year at a chosen site of deployment. It is found that control may be able to provide the required amounts of power to sustain instrument operation at the chosen site but also that energy storage options may be worth pursuing.