The water entry of slender axisymmetric bodies Physics of Fluids 26, 072108 (2014) Abstract. The investigation on free-surface impact of projectiles has last for more than one hundred years due to its noticeable significance on improving defensive weapon technology. Laboratory-scaled water entry experiments for trajectory stability had been performed with four kinds of projectiles at a speed range of 20~200 m/s. The nose shapes of the cylindrical projectiles were designed into flat, ogive, hemi-sphere and cone to make comparisons on the trajectory deviation when they were launched into water at a certain angle of 0~20°. Two high-speed cameras positioned orthogonal to each other and normal to the water tank were employed to capture the entire process of projectiles' penetration. From the experimental results, the consecutive images in two planes were presented to display the general process of the trajectory deviation. Compared with the effect of impact velocities and nose shape on trajectory deviation, it merited conclude that flat projectiles had a better trajectory stability, while ogival projectiles experienced the largest attitude change. The characteristics of pressure waves were also investigated.

In order to study the buffering effect of the structure when it enters the sea at high speed in the air, an effective test method is established in this paper. The experimental method can effectively observe the motion state of the structure body and the deformation process of the buffer structure, and the impact response data collected by the acceleration sensor provides an important reference for the research. The results show that the cushioning device installed on the head of the structure can effectively reduce the overload at the moment of water impact, and the choice of protective material will affect the cushioning energy absorption effect.

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