Date of Award:

8-2018

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Mechanical and Aerospace Engineering

Advisor/Chair:

Tadd T. Truscott

Abstract

When a sphere or a stream of water hits the surface of a pool of water and enters a crater or air cavity often forms. This topic has been studied, both formally and informally, for a long time. This dissertation investigates four areas of water impact that are still poorly understood using high-speed photography. First, it examines a stream of droplets impacting on a pool of water, similar to a faucet drizzling into a full bucket. For these types of impacts we predict the depth, diameter, velocity, and shape of the cavities that the droplet stream forms. Second, it examines what occurs when a sphere impacts a pool of soapy water, such as a bubble bath or kitchen sink. The minimum velocity for a cavity to form decreases when soap is present. If the water has bubbles on the surface, the sphere will always form a cavity. Third, it examines how different coatings on a sphere (car wax, etc.) affect whether the sphere forms a cavity, and it shows how the coating affect the shape of that cavity. Fourth, when objects impact a water surface they experience a large force, which many people have noticed when participating in cliff jumping, high diving, and belly flop competitions. We show that the force of impact can be reduced by 75% simply by allowing a mass of water to impact in front of the object.

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