Wave Power Generation Using Nonlinear Roll-Pitch Coupling in a Ship

When there is a two to one internal resonance ratio between the natural frequencies of the pitch motion and the roll motion of a ship, a nonlinear energy transfer occurs between the modes. If the ship is excited near the pitch natural frequency and at a large enough excitation amplitude, the pitch mode transfers energy to the roll mode. We use this interesting phenomenon to develop a wave power device for off-shore purposes. In this paper, we experimentally show that we can use a horizontal pendulum and use the quadratic nonlinear coupling between the pitch and the roll mode to get full rotation of the pendulum inside the ship. A rotating pendulum will generate orders of magnitude more power than a locally oscillating one when connected to a DC generator. This article measures the angle of the pendulum at the pitch frequency excitation of the ship to experimentally confirm the expected theoretical results on this phenomenon.