Effect of Stiffness Degradation of Clay in the Dynamic Response of Monopile-Supported Offshore Wind Turbines

Stiffness degradation studies for monopile-supported offshore wind turbines (OWTs) are usually limited to the geotechnical domain, largely ignoring the dynamic loads from the wind and the waves. This paper makes use of a time-domain approach, coupling aerodynamic and hydrodynamic loads, to investigate the influence of stiffness degradation in clay on the response of a monopile-supported OWT in a water depth of 20 m. p-y curves are used to represent the soil-structure interaction (SSI) in the lateral direction and a suitable degradation method is applied to consider the effects of cyclic loading. It is observed that the influence of stiffness degradation wanes with increasing number of load cycles. OWT's being highly dynamic structures; the debilitating effects of stiffness degradation cannot be entirely discounted.