Numerical and experimental investigation of nonlinear vortex induced vibration energy converters

In this paper, effects of bi-stable stiffness and hardening stiffness on the performance of a Vortex induced vibration (VIV) energy converter are theoretically and experimentally studied through a wake oscillator model and a computer-based force-feedback testing platform. Based on the simulation and experimental results, it is found that the bi-stable stiffness is potential to allow the system to operate at low velocity water flows, while the hardening stiffness will extend the operating range at high velocity flows. Subsequently, in order to take the advantages of both types of stiffness, a combined nonlinear stiffness is proposed and verified experimentally to demonstrate its capability in improving the overall operating range of the VIV energy converter.