USING IMAGE ANALYSIS TO QUANTIFY PROPAGATION SPEEDS AND STRESS ANISOTROPY IN GRANULAR ACOUSTIC EXPERIMENTS
Loading...
Authors
Bradley, Kylie C.
Subjects
granular material
nonlinearity
photoelastic
anisotropy
nonlinearity
photoelastic
anisotropy
Advisors
Clark, Abram H., IV
Date of Issue
2019-12
Date
Publisher
Monterey, CA; Naval Postgraduate School
Language
Abstract
Understanding how forces propagate through granular media is broadly relevant in acoustic and non-acoustic warfare applications. For example, sediment type can impact acoustic propagation during bottom bounce events that undersea assets use for navigation. There is not yet a complete theory of force propagation in granular media due to several nonlinearities, like friction and Hertzian contact interactions. Of particular interest is the crossover region between linear and nonlinear regimes, where the propagating stresses are comparable to the initial confining stress in the system, as well as the shock regime, where stresses greatly exceed confining prestress.
Aiming to develop more complete theories of force propagation in these regimes, we perform experimental impact tests and analyze how forces propagate in two-dimensional, frictional granular media. Assemblies of photo elastic disks are subjected to a vertical confining stress and then impacted from the side by a pendulum. Both the confining stress and the impact speed can be varied, and high-speed video captures the forces propagating through the material. We use image processing to quantify the speed of the moving wave and the force network’s structure. In particular, we focus on the phenomenology of the traveling shock and the stress anisotropy of the force networks, which has never before been experimentally measured.
Type
Thesis
Description
Series/Report No
Department
Engineering Acoustics Academic Committee (EAAC)
Organization
Identifiers
NPS Report Number
Sponsors
Funder
Format
Citation
Distribution Statement
Approved for public release; distribution is unlimited.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.