A preliminary study of a novel wave energy converter of a Scotch Yoke mechanism-based power take-off

Abstract

This work proposes a novel concept to harvest power from ocean waves using a Scotch Yoke mechanism to transmit the heave motion of the buoy into the rotation of an off-the-shelf rotary generator. The novel transmission mechanism is proposed to tackle some of the main obstacles of ocean waves energy harvesters associated with the reliance on resonance and the high expenses related to the large device dimensions and permanent magnet linear generators. The Scotch Yoke mechanism converts the linear wave motion of a harmonic nature into rotary generator motion, coinciding with the nature of ocean waves. A mathematical model is constructed relating the hydrodynamics of the float to the non-linear resistive forces of the power take-off. Simulations are conducted for two different devices, including a typical large-scale-up wave energy converter device and a relatively small scaled-down wave energy converter device that can be placed close to the shore. The simulation results showcase that the large scale device can have a peak harvesting efficiency of up to 42%, while the small scale device can have a peak harvesting efficiency of up to 34%. This is of great importance as the small device can be used with an off-the-shelf rotary generator, and can be placed close to the shoreline further lowering the cost of manufacturing, installation, and maintenance allowing easier access to the device. Also, to validate the concept, a small scaled-down device has been fabricated, and dry-tested. The tested power take-off is proven to be able to harvest energy from linear harmonic oscillating buoy motions with a peak efficiency of 49% (not including the hydrodynamic efficiency).