Hydrodynamic Characteristic Around the Riprap Protection of Monopile Wind Power Foundation with Scour Pit During Scour

Riprap protection is widely used in offshore wind power foundations. The boundary of riprap will change and affect the hydrodynamics around the foundation during scour. In this study, the experiment was conducted to obtain the topographic data of the riprap failure process. Then, a numerical model of current-pile-riprap-seabed interaction was set using the data to explore the hydrodynamic characteristics around the monopile during the process of stone moving under the action of current. The numerical model is verified through theory and test data. The results show that compared with an unprotected foundation, the maximum flow velocity and range of horseshoe vortex around the monopile with intact riprap will increase, while pressure around the monopile will decrease. During the process of scour, the riprap will sink and be scoured, resulting in increased water cross-section and a velocity decrease of 9.32% to 17.05%. In the process of riprap damage, the height of the diving flow increases, and the horseshoe vortex continuously decreases. The wake vortex near the surface remains stable during the process, while the wake vortex near bed gradually shrinks and disappears. Meanwhile, the pressure around the monopile increases, with maximum pressure increasing by 3.38 times.