Local scour of composite cylindrical wind turbine foundation on fine sand seabed under combined waves and current

The composite cylindrical wind turbine foundation is characterized by its large-diameter cylindrical base, which offers superior anti-overturning capability, and it is widely used in the soft soil seabed of Jiangsu, China. Due to its complex structural form, the local scour under combined waves and current significantly differs from that of monopile foundations. However, research on the scour characteristics specific to composite cylindrical wind turbine foundations remains scarce. A numerical model for local scour of wind turbine foundations was established in this study, which was verified with the field-measured scour data. A series of numerical simulations of local scour depths for composite cylindrical wind turbine foundations under various water depths and wave-current combinations were conducted. The simulation results indicate that the wake vortex shedding caused by the complex structural form leads to the local scour around the composite cylindrical wind turbine foundation; the normalized scour depth increases with the Keulegan-Carpenter number and the relative current strength; when the relative current strength is greater than 0.6, the influence of the Keulegan-Carpenter number on scour depth tends to be weakened; similarly, as the Keulegan-Carpenter number increases, the effect of the relative current strength on scour depth gradually diminishes. A scour equation of the composite cylindrical wind turbine foundation is suggested to predict the local scour in fine sand bed under waves and current.