Dynamic responses of OWT hybrid monopile-bucket foundations in sands under seismic and environmental loading

To improve the bearing performance of the monopile, the innovative hybrid monopile-bucket foundation has been put forward and successfully installed in offshore wind turbine (OWT) pilot projects in China in recent years. However, dynamic responses of hybrid monopile-bucket foundations in sands under seismic and environmental loading are not well covered in the literature. This study presents the development and validation of a three-dimensional numerical model for analyzing dynamic responses of OWT hybrid foundation in sands. Furthermore, this study reveals the rotational mechanism of the hybrid monopile-bucket foundations, examines the variation of pore pressure around the foundation, and investigates the displacement and acceleration responses of the OWT through extensive numerical simulations. It is found that the presence of the suction bucket can improve the soil's liquefaction resistance due to its constraint effect on the soil; the peak ground acceleration significantly impacts the rotation angle of the hybrid foundation, with strong earthquakes potentially causing substantial temporary and permanent rotation due to sand liquefaction; environmental loads, such as wind and waves, often amplify the seismic responses of OWT systems, for example, increasing the rotation angle of the foundation and tower, and accelerating soil liquefaction.