Numerical study of impact force and ricochet behavior of high speed water-entry bodies

Numerical method for computing impact forces and ricochet behavior of the water-entry body was developed. The present method assumes the impact occurs within very short time interval and the fluid viscosity effect does not have enough time to play a significant role during impact. That is, the flow around a water-entry body is assumed as inviscid potential flow and is solved by the source panel method. As the body enters into the water, the elements can be classified into three types of elements: (i) fully submerged into water, (ii) intersected by water surface and, (iii) fully outside of water. Since only submerged portion of the body is considered in the present impact analysis, the elements that are outside of water is excluded. The panels fully submerged into the water are routinely treated and the panels intersected with the water free surface are redefined and reorganized to be amenable to the source panel method. To validate the capability of computing impact forces of the present method, a disk cylinder and two ogives were tested and compared with experimental and other numerical data. Good agreements with those results were obtained. After the impact forces were determined, the ricochet off the free surface was simulated by coupling with the dynamic equations of two degrees of freedom, in case of the changes of the water-entry angle and the weight of the body.