Theoretical and experimental investigation on the advantages of auxetic nonlinear vortex-induced vibration energy harvesting

Due to its wide applicability, vortex-induced vibration (VIV) from wind and water flow has been explored for piezoelectric energy harvesting. However, the broadband VIV energy harvesting at low wind speeds is still a great challenge. In this paper, an auxetic nonlinear VIV energy harvester (ANVEH) is proposed. For the first time, the advantages of monostable softening behavior using magnetic attraction are investigated. It is found theoretically and experimentally that the monostable softening can broaden the working wind speed range whereas decreasing the peak energy output. Thus, the auxetic structure is proposed to compensate the decrease of peak energy output with the monostable softening due to its negative Poisson's ratio and high stress distribution. Utilizing the experimentally validated theoretical model, parametric investigations are undertaken to examine the effects of various factors, including the magnetic separation distance, the stiffness and mass of the harvester, the dimension of the bluff body, the connected resistance, and the electromechanical coupling coefficient. Results show that no matter how the system parameters vary, the ANVEH has the superior performance than the plain nonlinear VIV energy harvester (PNVEH).