Offshore wind energy is an important renewable electricity source in the UK and Europe.Monopiles are currently the most commonly used substructures to support offshore wind turbines. The fatigue life of offshore wind turbines is directly linked to the oscillatory bending stresses caused by wind and wave loading. The dynamic response of the structure is highly dependent on the combined aerodynamic, hydrodynamic, structural, and soil damping present.The fatigue life sensitivity of a reference 5MW wind turbine under operational and nonoperational conditions has been investigated using time-domain finite element simulations. The model uses beam elements for the monopile and tower and includes nonlinear p-y curves for soil-structure interaction. The effects of the wind turbine operation, environmental loads, and variable damping levels on the fatigue life were investigated systematically. The fatigue life increases significantly as a result of reductions in the bending stress caused by increased damping. From a practical point of view, significant cost-savings could be achieved in the design of a wind turbine by fitting supplemental damping devices. An efficient approximate method is proposed to assess the influence of damping, by scaling the vibration amplitudes around the first natural frequency of the system.

Offshore wind turbines supported on monopiles are an important source for renewable energy. Their fatigue life is governed by the environmental loads and in the dynamic behavior, depending on the support stiffness and thus soil‐structure interaction. The effects of scour on the short‐term and long‐term responses of the NREL 5‐MW wind turbine under operational conditions have been analyzed by using a finite element beam model with Winkler springs to model soil‐structure interaction. It was found that due to scour, the modal properties of the wind turbine do not change significantly. However, the maximum bending moment in the monopile increases, leading to a significant reduction in fatigue life. Backfilling the scour hole can recover the fatigue life, depending mostly on the depth after backfilling. An approximate fatigue analysis method is proposed, based on the full time‐domain analysis for 1 scour depth, predicting with good accuracy the fatigue life for different scour depths from the quasi‐static changes in the bending moment.