Seismic responses of offshore wind turbines based on a lumped parameter model subjected to complex marine loads at scoured sites

Numerous monopile-supported offshore wind turbines (OWTs) are located in earthquake-prone regions, and the complex marine environment further amplifies seismic responses of OWTs. To determine the seismic responses of OWTs efficiently and accurately, an integrated numerical model based on the OpenSees platform is developed. Dynamic soil-structure interaction phenomena are captured using lumped parameter models (LPMs) which are fitted to the soil-pile impedance functions, and the dynamic beam on Winkler foundation method is adopted, where the pile is discretized into finite elements. Following the validation, to present a comprehensive seismic analysis, the numerical model incorporates the effects of combined seismic, stochastic wind-wave loads and different scour depths (the primary influencing factor at scoured sites) simultaneously. The results indicate that seismic responses become more pronounced under combined loads, and seismic intensities and spectral characteristics also play an important role in it. As scour depth increases, the natural frequency of the OWT significantly decreases, and seismic responses are further exacerbated, affecting normal operations. Additionally, a comparison with the dynamic Beam on Nonlinear Winkler Foundation (BNWF) method indicates that the present method strikes a balance between accuracy and computational efficiency. This positions it as a practical and efficient option for investigating seismic responses of OWTs.