Large-scale experimental study on scour around offshore wind monopiles under irregular waves

The Keulegan-Carpenter (KC) number is the main dimensionless parameter that affects the local scour of offshore wind power monopile foundations. This study conducted large-scale (1:13) physical model tests to study the local scour shape, equilibrium scour depth, and local scour volume of offshore wind power monopiles under the action of irregular waves with different KC numbers. Systematic experiments were carried out with the KC number ranging from 1.0 to 13.0. With a small KC number (KC < 6), and especially when the KC number was less than 4, the scour mainly occurred on both cross-flow sides of the monopile with a low scour depth. When the KC number exceeded 4, the shape of the scour hole changed from a fan to an ellipse, and the maximum scour depth increased significantly with KC. With a large KC number (KC > 6), the proposed method better predicted the equilibrium scour depth when the wave broke. In addition, according to the results of three-dimensional terrain scanning, the relationship between the local equilibrium scour volume of a single offshore wind power monopile and the KC number was derived. This provided a rational method for estimation of the riprap redundancy for monopile protection against scour.