Dynamic modeling and analysis of improved wave energy harvesters with novel X-structured nonlinear inerter mechanism

Abstract

In this paper, a new passive mechanical structure, that is, an X-structured wave energy conversion system with a nonlinear inerter is proposed. The JONSWAP wave spectrum is utilized to simulate irregular waves, and the dynamic equations are deduced by the energy method and one-dimensional linear potential wave theory. The system response is calculated to analyze the performance of the nonlinear system. The potential benefits of nonlinear inerter are discussed in-depth. Increased inertance will result in a gradual decrease in resonance frequency. Whereas, when the inertance is larger than a certain limit value, the resonance frequency will be almost unchanged. Additionally, increasing the inertance helps to suppress the displacement and velocity of the system. This allows higher power to be captured without causing major damage to the mechanical structure of the system. More importantly, increasing inertance is conducive to improving the maximum power generated. In general, a nonlinear WEC system will capture more power than its linear counterpart and the case with no inerter, especially when with a small initial installation parameter. However, when the initial installation parameter becomes large, the nonlinear inerter system will capture less power than the linear inerter system and inerter-free system. This study provides innovative and novel insight into designing nonlinear ocean energy converters exploiting geometrical nonlinearities.