Passive structural control for wind turbine towers using a novel dual-track nonlinear energy sink

With larger rotors and taller towers developed to capture more wind energy, the tower structures become slenderer and more sensitive to wind loads, resulting in vortex-induced vibration (VIV) in both downwind and crosswind directions. The vibration control is faced with the challenges of broadband and multi-directional dynamic responses. Thus, this paper proposed a new type of dual-track nonlinear energy sink (NES) aimed to achieve the multi-mode and multi-direction vibration control of wind turbine towers. The two-degree-freedom coupled governing equations of the wind turbine tower with the dual-track NES are established and solved numerically, with full considerations of aerodynamics and fluid-solid interactions. Then, an optimized design of the dual-track NES is performed theoretically. To evaluate the vibration mitigation performance of the dual-track NES, a series of wind tunnel tests are carried out and analyzed further, in terms of the acceleration time-history response, statistical characteristics, frequency and damping ratio. It is demonstrated that the proposed NES functioning as an energy-dissipating device is efficient and robust in mitigating the dynamic response of wind turbine towers, even enabled to address the vortex resonance. It is remarkable that the dual-track NES can synchronously realize the vibration control in multi-mode and multi-direction by increasing the damping ratio of primary structure.