Numerical study on local scour characteristics of multi-bucket jacket foundation considering exposed height

Abstract

At present, offshore wind farms around the world have successively applied Multi-Bucket Jacket Foundations (MBJF), but little research has been done on the scour characteristics of MBJF. In this study, a three-dimensional numerical model is established to study the scour characteristics of large-diameter, wide-shallow, and multi-bucket foundations in deep water areas. The simulation results of the single pile foundation erosion based on this model are in good agreement with the existing experimental results. Also, an optimized grid division strategy is proposed based on a large number of comparative analyses, discussing the influence on the flow field, the bed elevation contour, and the scouring depth under different exposed height(h), bucket diameter(D), and bucket spacing(d) of the MBJF. Then, the influence of the upper structure on the scour characteristics is quantified. The results show that two sides of the buckets can form scoop-shaped scour holes with steep front and gentle back, with deposition of sand formed on the front and back sides. As the exposed height increases, the scouring depth initially shows an increasing trend, which then decreases. The scouring depth of the front row buckets decreases as the diameter increases, while it increases as the diameter for the rear row buckets increases. Compared with d=1.5D and d=3D, d=2D has the smallest scouring depth. Within the normal scale range, the maximum deviation coefficient of the influence of the upper jacket structure on the foundation scouring depth does not exceed 5.2%. Finally, based on V(velocity), H (water depth), μ (viscosity) the basic flow variables, the scouring prediction formula based on dimensionless parameters is obtained. The findings can be used to provide a reference for the design and scour protection of MBJF.