Optimal design of pendulum-tuned mass damper for the vibration control of offshore wind turbines with a flexible monopile foundation

This paper presents an optimal design of a passive-adaptive Pendulum-Tuned Mass Damper (PTMD) to mitigate the structural vibrations of an Offshore Wind Turbine (OWT) with a flexible monopile foundation considering the Pile-Soil Interaction (PSI). The OWT is based on the 5-MW baseline proposed by the National Renewable Energy Lab. The PSI is designed by a pile modeled as beam-column elements supported by nonlinear springs for lateral loads (p-y curves) and axial loads (t-z and Q-z curves), applied at the nodal points between the elements. The estimation of wind and wave spectra, as well as the hydrodynamic and aerodynamic loads, are conducted by using an in-house built MATLAB ® routine working together with an ANSYS ® 3-D finite element global model for evaluating the resultant peak displacement response at the OWT hub by a power spectral density analysis. Optimum design cases of PTMD parameters are obtained by a parametric analysis evaluating the dynamic response along and across directions at the hub and the resultant stress at the base of the tower. These responses and stress are evaluated as a function of the wind velocity at the hub.