Evaluation of seismic response of monopile foundation of offshore wind turbines in sandy soil by numerical modeling

Because of the development of wind turbine farms in seismic areas, such as East Asia, southern Europe, and the United States, as well as the importance of the foundation of the wind turbines in the design and implementation, it is necessary to study the seismic behavior of wind turbine foundations. In this study, the seismic behavior of monopile foundation of a simplified offshore wind turbine model under a specific earthquake record was evaluated by using finite element method in OpenSees software. At first, the proposed numerical model was validated by the results of a dynamic centrifuge modeling of a steel pile located in sandy soil. Then, the effects of various parameters such as dimensions of monopile (diameter and length), soil relative density, end bearing pile effect and wind load effect were evaluated. The results of this study showed that the changes of these parameters have significant effects on the seismic behavior of the monopile of offshore wind turbines. Increasing dimensions of monopile (diameter and length) and soil relative density improves the seismic performance of the structure and foundation system and reduces lateral displacement at the top of tower and reduces settlement and rotation of the monopile. Chang of behavior of the monopile from frictional pile to end bearing pile, improves the behavior of the wind turbine structure and foundation under seismic loading. Also, wind loading causes more displacement and rotation to the structure, and static wind load creates more critical conditions than the dynamic wind load.