Mitigating vortex-induced vibrations of off-shore wind turbine towers using magnetic damper with nonlinear stiffness and eddy current damping

Wind turbine towers (WTT), as tall slender structures, are exposed to complex loading conditions that may cause excessive oscillations affecting structural fatigue life and cost of maintenance; in this regard, vortex-induced vibration (VIV) is a challenging phenomenon to mathematically formulate and attenuating its resulting response in structures through added structural damping requires certain measures especially during assembly. Passive structural control devices have proven to be an effective solution in reducing structural vibrations and certain attributes of novel devices proposed in the literature could be exploited in new applications in a manner to overcome the limitations imposed by traditional dampers. In this paper, the effect of a magnetic damper with nonlinear stiffness and eddy current damping on VIV in off-shore WTT at four stages of installation is numerically investigated. Maximum VIV response of the tower is formulated using a spectral model for the off-shore DTU 10 MW reference wind turbine (RWT), taking into account the feasibility of implementing the device in terms of required space. The study reveals that the nonlinear damping device, in a compact and portable configuration, is capable of mitigating relative maximum normalized displacement and harmonic response due to VIV in off-shore WTTs at different installation stages. Based on the obtained results, the damper may be used as an installation aiding device to help facilitate tower erection and turbine assembly.