A quasi-zero stiffness two degree-of-freedom nonlinear galloping oscillator for ultra-low wind speed aeroelastic energy harvesting

Inspired by the capability of quasi-zero stiffness (QZS) nonlinearity to maintain a low dynamic natural frequency in vibration isolation and considering the easy manipulation of modal frequencies of a two degree-of-freedom (2DOF) structure, we propose a 2DOF QZS nonlinear galloping energy harvester for advanced wind power generation at ultra-low wind speeds. Conventional 1DOF and 2DOF linear harvesters produce relatively low voltage outputs at low wind speeds, while the commonly acknowledged bistable harvester is trapped in intra-well oscillation when the wind speed is low, also resulting in poor energy harvesting performance that makes it difficult to meet the power requirements for microelectronic devices in practical applications. The 2DOF QZS GEH is shown to significantly outperform the 1DOF linear, 2DOF linear, and 2DOF bistable harvesters, especially over the low wind speed region. A distributed-parameter aero-electro-mechanically coupled theoretical model is established and validated by wind tunnel experiments on a fabricated prototype. The 2DOF QZS GEH improves the voltage output by about 220 % at the wind velocity of 2.5 m/s as compared to the 1DOF linear counterpart and almost 100 % as compared to the 2DOF linear counterpart. The effects of key parameters, including the nonlinear stiffness, mass ratio and frequency ratio between two degrees of freedom, electromechanical coupling strength, and loading resistance, on the voltage and power output performance of the 2DOF QZS GEH are investigated. The results of this article provide a guideline to enhance the performance of nonlinear 2DOF QZS GEHs at low wind speeds from an experimental and theoretical point of view.