Utilization of Nonlinear Resonance of Vessels for Ocean-Wave Power Generation
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This research presents a method to utilize the pitch-roll nonlinear energy transfer phenomenon in vessels for off-shore wave power generation. The system proposed here is a power generator which is a horizontal pendulum on board of a vessel. The surface waves result in rocking of the vessel, which in turn results in rotation of the pendulum. The pendulum is connected to a DC generator. The design in this paper utilizes the nonlinear coupling between the roll and pitch motions of the generator vessel. The natural frequency of the pitch motion of the vessel is twice the fundamental frequency of the roll motion. In this specific condition when the vessel is excited in the pitch direction, the energy is nonlinearly transferred to the roll mode and the vessel oscillates in the roll direction. It is shown that the combination of the pitch and roll motions is far superior to the pitch motion since the combination results in full rotations of the generator pendulum. A pendulum in full rotations generates orders of magnitude more power compared to a locally oscillating pendulum. Experimental investigations are carried out to examine if the pendulum performs complete rotations when there are coupled pitch and roll oscillations in the vessel near the pitch resonant frequency. The experimental results show the occurrence of non-linear coupled motion in the vessel and the pendulum also performed spin motion about the axis of rotation.