Vibration control of monopile offshore wind turbine using a novel bi-directional rail variable friction pendulum-tuned mass damper

Monopile Offshore Wind Turbines (MOWTs) are vulnerable to multi-hazard effect. When these loads act on the MOWT simultaneously, the lateral dynamic response of the wind turbine significantly increases. This paper introduces a Bi-directional Rail Variable Friction Pendulum-Tuned Mass Damper (BRVFP-TMD) for the bidirectional vibration reduction of Wind Turbines (WTs). This device consists of two orthogonal rails with linearly varying friction coefficients, which can effectively control vibrations of wind turbine in two orthogonal directions. The performance of the BRVFP-TMD is evaluated by taking the example of the National Renewable Energy Lab (NREL) monopile 5 MW baseline wind turbine model. Through the Euler-Lagrange equation, a 12-degree-of-freedom (DOF) dynamic analysis model for MOWTs under uncontrolled conditions is established, and a 14-DOF dynamic model equipped with the BRVFP-TMD at the nacelle is created. Numerical models for aerodynamic, hydrodynamic loading and seismic effect for the MOWTs are developed through the principle of virtual work, considering soil effects through elastic bearing supports. The parameters of the BRVFP-TMD are optimized for the reduction of the displacement of nacelle and tower. The vibration reduction performance is also compared with that obtained from the Bi-directional Tuned Mass Dampers (BTMDs). Simulation results demonstrate that the novel BRVFP‑TMD provides considerable vibration control efficiency on the nacelle displacements than that of conventional bi‑directional viscous TMDs. And the calculated stroke of the device under all load conditions remains within the spatial limits of the nacelle, indicating favorable engineering applicability. Additionally, the damping devices installed in the nacelle exhibit negligible influence on the blade vibration.