Water impact of a surface-patterned disk

Abstract

Solid objects impacting on the free-surface experience peak force at the initial stage. The impact force often causes structural damage to the biological bodies and mechanical systems that cross the air-water interface. Present study proposes a novel way of reducing impact force by surface-patterning. Disk was chosen as an impacting body and the mesh-like surface-pattern was applied on the bottom of the disk. The maximum impact force reduces as the total volume of holes created by the surface patterns increases, and the reduction in dimensionless maximum impact force is characterized by the dimensionless volume of holes. The air is entrapped inside the holes when a surface-patterned disk enters the free surface. The rise and fall of impact force entails the compression and depressurization of the entrapped air bubbles during initial impact phase. Analysis on the impact duration reveals that the increase in the volume of entrapped air leads to the increase in impact duration. The extension of impact duration accompanies the reduction in maximum impact force while maintaining the impulse.