Numerical study of a point absorber wave energy converter with tuned variable inerter

Abstract

This paper introduces a novel point absorber wave energy converter (WEC) with tuned variable inerter (TVI). Originally, the tuned inerter (TI), consisting of a tuning spring, an inerter, and a dashpot element, was introduced in the field of civil engineering as a control device for structures subjected to seismic loadings. Moreover, a point absorber WEC equipped with TI, in which a motor is used for the dashpot element, has been proposed and its effectiveness has been shown. However, since the TI mechanism takes advantage of the resonance of the inerter to absorb energy from vibrating buoys, it has been pointed out that the TI could not respond well to the dominant period changes of ocean waves. Thus, for further improvement, a system to control the inerter is developed because the effective period is determined by the tuning spring stiffness and the inerter. In this system, the dominant wave period is calculated by the Fast Fourier Transform using the wave amplitude and the inerter and the motor current are adjusted accordingly. Numerical results obtained from the WEC-Sim showed that the proposed TVI system responded appropriately to the wave period changes and works better than the TI system.