Dynamic modeling, approximate solution, and performance analysis of an umbrella-shaped in-situ wave energy converter with a compact nonlinear stiffness mechanism

Abstract

The lack of continuous energy supply is a key challenge limiting the application of ocean robots in long-endurance and high-load observation operations. Capturing wave energy for power generation is an innovative approach to extend the endurance of ocean robots. This paper proposes a simple and compact nonlinear stiffness mechanism (NSM) to improve the energy capture efficiency of the umbrella-shaped in-situ wave energy converter (UIWEC). A nonlinear time-domain dynamic model with multi-degree-of-freedom coupling is established, and a frequency-domain approximate solution method for the motion response is proposed. Through the analysis of static characteristics and dynamic responses, the influence rules of NSM parameters on UIWEC are revealed. The numerical results show that the reasonable selection of NSM parameters can significantly improve the capture efficiency of UIWEC under irregular wave excitation. Under the common wave conditions in the South China Sea ($T_p=5s,H_s=1m$), the theoretical average wave energy capture power of the nonlinear stiffness UIWEC is 29.13 W, which is increased by 40.3 % compared with the linear stiffness UIWEC. This study provides a feasible solution for improving the efficiency of small-scale in-situ wave energy converter and it is expected to address the energy supply challenges faced by ocean robots during their long-term operation in the deep and open sea.