Effect of water depth on the Archimedean screw dynamics in air–water–sand media: A CFD–DEM study

The Archimedean screw is a specialized propulsion device for soft terrain, yet its mechanism in amphibious transition environments remains poorly understood. This study applies a coupled computational fluid dynamics (CFD) and discrete element method (DEM) to examine the screw’s kinematics and dynamics over a range of water depths. Slip ratio is adopted as the primary performance metric, and the numerical predictions achieve an average relative error of 6.22% compared with experimental results, confirming the model’s validity. The results indicate that increased water depth amplifies slippage during startup but improves pitch stability and reduces slip during steady motion, with slip ratio rising in proportion to sinkage. Particle interactions overwhelmingly govern thrust and resistance torque, while direct fluid forces and torques are negligible apart from buoyancy effects. Two additional coupling mechanisms are identified: air infiltration when the water and sand interfaces coincide, which disrupts the pore structure, increases sinkage, and degrades performance; and large variations in excess pore water pressure under full submersion, which weaken stress transmission and impair propulsion. These results provide a theoretical foundation for the design and optimization of Archimedean screws in complex multiphase environments.