Microscopic investigation of shape effect on local scour around the monopile using CFD-DEM

Local scour refers to the erosion or migration of sedimental particles around bridge piers or abutments under the action of water flow. It can potentially undermine the hydraulic structures, resulting in catastrophic damage or even collapse. Under various hydraulic conditions, monopiles with diverse cross-sectional shapes have increasingly been applied to marine foundations. This study aims to investigate the effect of monopile shapes on scour development, and to establish a cross-scale connection between the macroscopic evolution of scour pits and the microscopic characteristics of sediments. The scour processes around monopiles are simulated using a coupled computational fluid dynamics and discrete element method (CFD-DEM). Four monopile shapes are examined, including circular, square, square with rounded corners, and diamond. Macroscopic characteristics such as seabed morphology, maximum scouring depth, and scour areas are analyzed, along with the microscopic characteristics such as the kinetic energy, drag force, and mechanical coordination number. The outcomes highlight that the diamond-shaped pile results in the greatest scour depth and widest scour areas compared to the other shapes. The incorporation of rounded pile corners improves flow characteristics and mitigate scour pit development. Furthermore, the local scour at different areas around the monopiles varies under the influence of different flow features.