Impact force alleviation effect of surface pattern on disk falling onto water surface

Impact force during water entry is a limiting factor in the design of air-water amphibious systems. We report mitigation of the impact force by patterning a macroscale mesh of square holes on a flat disk falling onto water. The air trapped in the square holes cushions the impact; the air pressure slowly rises then falls, lengthening the impact duration and relieving the peak impact force. While the size and falling speed of the disk determine the total impulse, the alleviation effect is affected by the total volume of holes but not the falling speed and pattern geometry. Theoretical analysis agrees with our experimental results.