Seismic response analysis of offshore wind turbines supported by monopiles on gently sloping sandy seabed

Many nearshore and offshore seabeds are classified as gently sloping seabeds, typically with an inclination angle of less than 10°. This study employs a time-domain coupled dynamic analysis model to investigate a monopile foundation supporting a 5-MW offshore wind turbine (OWT) on a gently sloping sandy seabed, using the finite element software OpenSees. The feasibility of the numerical model for simulating the seismic response of a gently sloping sandy seabed was validated through Liquefaction Experiments and Analysis Projects (LEAP) centrifuge tests. The results indicate that the excess pore water pressure (EPWP) in the sloping seabed is influenced by the interaction between the initial shear stress and the lateral movement of the seabed. The maximum horizontal displacement of OWTs is significantly affected by the seabed slope angle, with the impact occurring through the rotation of the OWT monopile. As the EPWP increases, the dominant vibration frequency of the OWT system tends to approach the natural frequency of OWTs, resulting in a larger horizontal displacement. This process is affected by factors such as the peak of the seismic motion, seismic frequency, and the seabed slope. These findings provide key insights for improving OWT monopile stability under gently sloping seabed conditions.