Soil Masing Behaviour for Offshore Wind Turbines—Fatigue Design and a Simple Damping Model

ABSTRACT Fatigue damage accumulation for offshore wind turbines is highly dependent on damping of the structure and particularly on the soil damping contribution during idling conditions. This paper presents an efficient method to estimate soil damping specific to wind turbine design and offshore environmental conditions. The method assumes a narrow‐banded response, suitable for turbines in low damping conditions. The proposed method demonstrates that soil damping varies significantly with load level and that predictions can be improved over the common industry practice of assuming a constant soil damping value. The fatigue damage predicted using this proposed method is calibrated using a multi‐surface plasticity foundation model. The structural response with this plasticity model is also compared to linear elastic soil modelling without any soil damping. This analysis shows that significant reductions in damage may be observed when soil Masing behaviour is incorporated. Overall, this paper shows that soil plasticity, and its variation with load level, should be included within a design framework and suggests a straightforward way of doing so.