Study on water entry into shallow-water current using smoothed particle hydrodynamics method

Abstract

Water entry is a typical problem in shipbuilding and ocean engineering. When the ship entering shallow-water current, the combined effects of current and water bottom will complicate the fluid field and further affect the hydrodynamic responses of the ship. In this paper, a two-dimensional bow section entering shallow-water current is studied by smoothed particle hydrodynamics method and the accuracy of the method is first validated. Then, the flows around the hull in shallow and deep water are compared. It is found that the shallow water will produce a more significant effect of flow around the hull, resulting in an increasing in the diffusion velocity of the vortex structure and the related flow-induced forces. The asymmetry of free surface is more obvious in shallow water. Furthermore, the water entries into current and into still water under different water depths are simulated, respectively. When entering shallow-water current, several asymmetrical stagnation-point regions will be induced, which intensify the variation and asymmetric distribution of velocity in the fluid around the hull. Due to the bottom effect in shallow water, the pressure on the hull's lower part increases and two obvious pressure peaks will be caused. The influence of water depth on the pressure gradually disappears as the gauging point gets higher. Accordingly, the vertical force under shallow water also has two peaks and is higher than that under deep water. Moreover, when entering shallow-water current, there will be a greater decrease in vertical velocity than entering still water.