Abstract
This paper proposes an electromagnetic bi-stable energy harvester (EBEH) with tunable stiffness for scavenging the hydrokinetic energy from flow-induced vibration (FIV) scenarios. A mathematical model of the magneto-mechanical–electrical coupling system is established considering vortex-induced forces, wake oscillator effect, negative linear stiffness and hybrid excitations. The bi-stable system with adjustable barrier height is employed to enhance state-of-the-art energy scavenging performance of vortex-induced vibration (VIV). Preliminary verification with regard to VIV within a lock-in wind speed range has been implemented by means of CFD simulation. The nonlinear energy transfer capacity and energy conversion performance of the FIV based EBEH are evaluated under solitary vortex-induced vibration (VIV) and hybrid excitations. Simulation results show that EBEH with larger negative linear stiffness has higher energy conversion efficiency and target energy transfer capacity in a wide range of inlet velocities. The large amplitude and low frequency vibration of the VIV of the cylinder is mainly caused by the lift pulsation, meanwhile the small amplitude and high frequency galloping are caused by the perpendicular component pulsation of the drag force. The fluctuations of the lift/drag coefficient at different inflow velocities are directly related to the VIV or galloping amplitude of the cylindrical bluff body. Specifically, the frequency fD is approximately twice the frequency fL in a wide inflow velocity range; The amplitude of fluctuating lift exceeds 2.0 in a wide range of inflow velocity from 1.0 m/s to 20 m/s. The nonlinear energy transfer efficiency of the FIV based EBEH with smaller barrier height is greater than 60% when the inflow velocity ranges from 20 m/s to 30 m/s. The nonlinear energy transfer capability of EBEH with appropriate negative stiffness outperforms its counterpart of cubic stiffness more than ten times. The maximum mean harvested power achieved from EBEH can be increased over 900% than that of the cubic stiffness case. Regardless of negative stiffness alteration, the optimal external load that maximizes the EBEH output power is around 50 Ω. Additionally, when the vortex-induced vibration cannot be woken, intervention of base excitation causes considerable chaotic motion consisting of aperiodic intra-well and inter-well snap-throughs at low inflow velocities. Nevertheless, nonlinear energy transfer efficiency of bi-stable energy harvester is slightly crippled with the increase of the base excitation intensity.