Water entry of deformable spheres

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 has been studied for over a century, this work focuses on the water entry characteri...

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Bibliographic Details
Published in:Journal of fluid mechanics 2017-08, Vol.824, p.912-930
Main Authors: Hurd, Randy C., Belden, Jesse, Jandron, Michael A., Tate Fanning, D., Bower, Allan F., Truscott, Tadd T.
Format: Article
Language:English
Subjects:
Coefficients
Deformation
Deformation effects
Deformation mechanisms
Dynamics
Elastomers
Experiments
Formability
Free surfaces
Hydrodynamic pressure
Hydrodynamics
Image processing
Imaging techniques
Oscillations
Properties
Rigid-body dynamics
Shear modulus
Spheres
Studies
Velocity
Vibration
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Summary: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 has 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, an elastomeric sphere deforms significantly, giving rise to 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 behaviour 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 the 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.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2017.365