A Pivoting Tensioned Offshore Wave Energy Converter with a Motion Rectifier System

The exploitation of wave energy, as already observed in literature, may provide a significant contribution to the generation of clean energy, in accordance with the recent policies aimed at a supporting a sustainable development of energy markets. Nonetheless, several problems are still discussed in the vast literature on this topic and prevent the full achievement of a commercial maturity level for the technologies based on such principle. This paper introduces a wave energy conversion system based on the concept of the wave actuated bodies, comprising two floaters linked together using hinged lever arms. One of the bodies (indicated as the buoy) is left free to rotate around a hinge axis connected to the other body (indicated as platform) which is linked to the seabed by means of tensioned mooring lines needed to reduce the platform motion, thus allowing to increase the relative motion between the two bodies. The lever arms connecting the buoy and the platform are, in fact, linked to a shaft, hinged on the platform; the oscillations of the shaft are then exploited to generate mechanical power supplied to an electrical generator. This study introduces also a mechanical rectification system along the kinematic conversion chain. The alternative and slow oscillating motion, induced by the waves, represents, indeed, a detrimental condition for the operation of typical rotary electrical generators the efficiency of which is maximized when the motion is unidirectional with high and, possibly, constant speed. Thus, in order to improve the overall conversion efficiency, a mechanical rectification system is inserted between the input shaft and the generator so that such system, relying on the use of unidirectional clutches or freewheels, is able to convert the two-way rotational oscillations into a one-way rotation at the generator input. The oscillations of the rotational speed at the generator input are further reduced by the means of a conventional flywheel. The paper presents the main concept of the system under development and the preliminary studies aimed also at the development of an experimental dry test bench to prove the feasibility and the effectiveness of the proposed wave energy conversion device.