Examining the interplay between body shape and stiffness for improving water entry

When a high-velocity rigid body breaches the water surface, the resulting impulse force, while brief,

is significantly high, and often damaging to the body. Here, experimental results show that a segmented

body with a single programmable stiffness element coupled with a nose cone and cylindrical after-body, can

mitigate high-velocity impact forces. Programming the stiffness allows the body to increase the impulse force

duration, and thus, alter the severity of the impact. Utilizing experimental prototypes with 25°, 45°, and

60°half-angle cone shapes, our findings show that the impulse force time decay and cavity shape evolution

can be manipulated directly by varying the stiffness between the segments. The study also demonstrates

the importance of the interplay between the cone shape and body stiffness. Notably, a body with 60°cone

exhibits the highest reduction in maximal impact acceleration, approximately 60% from the initial value of

17.0 g to 6.5 g for the rigid and a spring case, respectively. A preliminary discrete dynamic model is provided

for estimating the impulse forces for bodies with and without segmentation. The model shows reasonable

agreement with the experimental results.