Nonlinear ocean energy harvesting method for unmanned surface vessels

Long endurance unmanned surface vessels (USVs) play a critical role in ocean monitoring, but traditional energy supply for their monitoring sensors has great problems. Harvesting wave-induced ship vibration energy is a promising solution to meet the long-term energy demands of USVs. However, traditional linear energy harvesters (L-EHs) exhibit poor performance in capturing wave-induced low-frequency vibrations. To address this issue, a bistable mechanism is introduced, and a bistable spring-mass-based EH (B-EH) is studied as an embodiment. A wave-to-wire dynamic model of the B-EH in the USV is established, and a semi-analytic solution method based on the least square method and the harmonic balance method is proposed for the fast solution of the nonlinear electromechanical coupling equations. Furthermore, the static characteristics of the B-EH and the influence of the main parameters on the average power of the B-EH are studied. The results show that the B-EH with proper parameter design has a wider bandwidth at low frequencies compared to the L-EH, making it more suitable for the long-term energy supply of the USV during operation. The bistable mechanism holds great potential to be widely used in inertial type EHs for USVs.