Mitigating Wind-Wave Misalignment Induced Vibrations in Semi-Submersible Offshore Wind Turbines using a 2D Adjustable Nonlinear Tuned Mass Damper

This paper addresses the issue of wind-wave misalignment that causes excessive vibrations in floating wind turbines operating in harsh environments. A two-dimensional adjustable nonlinear tuned mass damper (2D-ANTMD) is proposed to mitigate the structural response. The 2D-ANTMD consists of a concentrated mass and two pairs of spring dampers, with the angle between the springs being adjustable to create different nonlinear restoring force characteristics. This feature allows the 2D-ANTMD to adapt to varying wind-wave misalignment conditions, which is an advantage over traditional tuned mass dampers (TMDs) with fixed springs. The parameters of the 2D-ANTMD are optimized using a numerical search method, and its vibration control performance is evaluated on the NREL 5MW semi-submersible wind turbine model. The results show that the 2D-ANTMD can achieve further improvements in vibration control with a smaller mass ratio, effectively suppressing the roll and pitch vibration responses of floating wind turbines under various wind-wave misalignment conditions across a range of environmental loads. Moreover, the 2D-ANTMD is capable of attenuating vibrations not only at the dominant frequency but also over a wider frequency range, which is a unique feature of nonlinear TMDs. These findings provide new insights into the design of nonlinear TMDs and adaptive control of floating wind turbines under complex environmental conditions.