# Water entry of deformable spheres

## TL;DR

This study investigates how deformable elastomeric spheres behave upon water entry, revealing that their deformation and vibration significantly influence cavity formation and can be predicted from material properties and impact conditions.

## Contribution

It is the first experimental analysis of water entry dynamics of deformable spheres, linking deformation and oscillations to impact parameters and material properties.

## Key findings

- Deformable spheres create nested cavities due to material oscillations.
- Deformation and vibration can be predicted from material and impact parameters.
- Effective diameter accounts for deformation, aligning with rigid sphere characteristics.

## Abstract

When a rigid body collides with a liquid surface with sufficient velocity, it creates a splash curtain above the surface and entrains air behind the sphere, creating a cavity below the surface. While cavity dynamics have been studied for over a century, this work focuses on the water entry characteristics of deformable elastomeric spheres, which has not been studied. Upon free surface impact, elastomeric sphere deform significantly, resulting in large-scale material oscillations within the sphere, resulting in unique nested cavities. We study these phenomena experimentally with high speed imaging and image processing techniques. The water entry behavior of deformable spheres differs from rigid spheres because of the pronounced deformation caused at impact as well as the subsequent material vibration. Our results show that this deformation and vibration can be predicted from material properties and impact conditions. Additionally, by accounting for the sphere deformation in an effective diameter term, we recover previously reported characteristics for time to cavity pinch-off and hydrodynamic force coefficients for rigid spheres. Our results also show that velocity change over the first oscillation period scales with a dimensionless ratio of material shear modulus to impact hydrodynamic pressure. Therefore we are able to describe the water entry characteristics of deformable spheres in terms of material properties and impact conditions.