Date of Award:

12-2021

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Mechanical and Aerospace Engineering

Committee Chair(s)

Tadd T. Truscott

Committee

Tadd T. Truscott

Committee

Barton Smith

Committee

Jesse Belden

Committee

Som Dutta

Committee

John S. Allen

Abstract

Projectile impacts in quiescent water pool are synonymous with intriguing splash phenomena and rich underwater physics. Depending on the material property, geometry and surface conditions of the impacting projectiles coupled with the geometric properties of the water pool (e.g., depth, width etc.), contrasting events like sub-surface cavity formation or bouncing of macro-droplets unfolds over millimetric timescales.

In this dissertation, I present four different studies that look at different aspects of impact events with the help of high-speed imaging techniques and implementation of other sensory data acquisition instruments. Firstly, I look at the force of impact associated with projectile water entry and the means of reducing said impact force through consecutive entry of projectiles. I show through a canonical sphere study that by means of consecutive entry of spheres, I can reduce the initial peak impact force felt by the second sphere. I extend this idea of multiple sphere water entry problem with a second study looking at side-by-side entry of spheres at low impact velocities. The close proximity of the two sphere-induced cavities break down the symmetric nature of the otherwise axisymmetric cavity formation mechanism, influencing a wide range of important cavity parameters such as deep-seal pinch-off time, creation of the surface Worthington jet and underwater trajectories of the impacting spheres. Thirdly, I look at the characteristic times relating to sealing of underwater cavities created through water entry of projectiles, especially the intermediate-speed (30 m/s - 165 m/s projectile impact speed) surface seal cavities. Lastly, I look at deformable spheres impacting macro-water droplet resting on a hydrophobic surface and study a previously unknown droplet bouncing mechanism seen only for the deformable viscoelastic spheres.

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