Vortex-Induced Vibration (VIV) hydrokinetic energy harvesting based on nonlinear damping

The Vortex-Induced Vibration (VIV) hydrokinetic energy converter can be used to harvest low-speed ocean current energy. In order to match the nonlinear resonance response in VIV, the nonlinear damping model is proposed. A two-way CFD numerical model is developed to simulate the VIV responses. The nonlinear damping model (C_t=C_max(V_t/V_max)ⁿ) contains two control parameters: C_max is the maximum preset damping; n is the model exponent. In the nonlinear damping model, when the vibration velocity is low, small damping is adopted to reduce resistance for VIV; when the vibration velocity is high, large damping is adopted to enhance energy transfer performance. It can be found that nonlinear damping is more efficient than constant damping, thereby improving the adaptability of the converter. Besides, the optimal nonlinear damping model belongs to a concave function. For the concave function model, the damping changes sensitively when the vibration velocity is high; when the vibration velocity is low, the damping remains stable. The effects of the model parameters on the VIV response and converted power are nonlinear, so a ridge-shaped fitted response surface of the vibration power is observed. Finally, after introducing nonlinear damping, the vibration power is significantly improved when compared to the optimal constant damping.