Date of Award:

8-2021

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Mechanical and Aerospace Engineering

Committee Chair(s)

Tadd T. Truscott

Committee

Tadd T. Truscott

Committee

Doug Hunsaker

Committee

Kelli Hendrickson

Abstract

When an object enters water, a crater, or air cavity, can form around the object and remain attached as the object travels underwater. Cavities can be beneficial and reduce drag force but there may be times when the cavity needs to be removed. This research proposes a method to remove air cavities by letting air leave the cavity, deflating the cavity similar to how a balloon is deflated. To provide air a path to leave the cavity, a tube with vent holes is attached to the object. The vent holes are located near the object, where the air cavity forms, and allow the air to move from the cavity out through the tube. Cavities for objects with and without the vented tube are compared using images from a high-speed cameras. Different vented tube lengths, vented tube diameters, vent hole areas, and impact velocities are compared. If the vented tube is long enough that it is outside of the cavity then the air will leave and the cavity deflates. As the vented tube length and vented tube diameter increase, the amount of air that leaves the cavity increases. Similarly as vent hole area increases, the amount of air that leaves the cavity increases until the holes get too large and the cavity fills with water before all the air can leave, trapping the remaining air in the cavity. How impact velocity effects the amount of air that leaves the cavity depends on the vented tube length. The critical vented tube length required for deflation to occur depends on the sphere radius, impact velocity, and vented tube diameter. The noise the cavity makes and the acceleration of the object as it travels underwater are compared for deflating cavities and non-deflating cavities and the results show that cavity deflation reduces both noise and acceleration.

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