On the performance of multi-stable wave energy converter

Abstract

The thesis investigated the performance of multi-stable wave energy converter (WEC). First, the static analysis of the two-/three-/four-spring coupled WEC found that these WECs have mono-/bi-/tri-/quad-stable modes under specific spring parameters. Then, the dynamic analysis of bi-/tri-/quad-stable WECs is conducted, and the performance of these WECs is evaluated mainly from three aspects: the efficiency, the frequency bandwidth and the device robustness. Compared with the bi-stable mode generated by two-spring coupled WEC (conventional bi-stable WEC or CB-WEC), it is found that part of the bi-stable mode generated by three-/four-spring coupled WEC (improved bi-stable WEC or IB-WEC) has higher efficiency, wider frequency bandwidth and larger robustness against the PTO damping disorder and sea state changes. Furthermore, a tri-stable WEC (Tri-WEC) and a quad-stable WEC (Quad-WEC) are selected and compared with IB-WEC. Results show that these two WECs can achieve higher efficiency than IB-WEC, especially under ultra-low-energy sea states. Moreover, their robustness against PTO damping detuning and sea state changes is also more substantial than IB-WEC. Finally, the four-spring coupled WEC (FS-WEC) performance is assessed at a specific sea site. The power output performance comparison with linear WEC (LN-WEC) shows that the well-tuned FS-WEC has higher energy production and smoother power output flow. The study also shows that the robustness of the FS-WEC against spring parameter changes increases as wave energy level increases.