Dynamic Response and Load Transfer Mechanisms of Monopile Offshore Wind Turbines Subjected to Scour Effects

Scour-induced degradation of soil–structure interactions (SSIs) may substantially amplify the dynamic response of monopile offshore wind turbines (OWTs) under combined environmental and seismic loads. To clarify this mechanism and provide guidance for the safety assessment of OWT foundations, this study establishes a coupled numerical model considering wind, wave, earthquake, scour, and SSI effects. Based on this model, the DTU 10 MW OWT is selected as the research object, and its dynamic responses are investigated with different scour morphologies, scour depths, earthquake inputs, and selected soil parameter sets. The results show that scour reduces the lateral stiffness of the soil–structure system, shifts the structural natural frequency toward a lower-frequency range, and amplifies the displacement, acceleration, and stress responses under seismic excitation. With the selected M8 earthquake input, the tower top displacement reaches 4.18 m in the global-2D scour case, which is more than twice that in the non-scoured case. Global scour produces stronger response amplification than local scour because it weakens the SSI constraint around the full circumference of the pile. For the selected soil parameter sets and the adopted p–y formulations, the clayey foundation model produces smaller calculated displacement and stress responses than the sandy foundation model, reflecting differences in the prescribed lateral stiffness and ultimate soil resistance. These results provide comparative insights for the seismic assessment and scour-resistant design of monopile OWT foundations.