Date of Award

1995

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering and Applied Mechanics

First Advisor

Martin H. Sadd

Abstract

A numerical study of wave propagation in fluid saturated granular materials is presented. Because of their microstructure, granular materials are multi-phase, composed of solid particles along with pore fluid and/or gas. The mechanical response of such materials is quite complicated and difficult to model with classical continuum mechanics. Due to the microscopic heterogeneity of the particulate media, wave propagation in porous or granular materials is governed y complex physical behaviors which are sensitive to slight variations in fluid content or of the solid microstructure.

The numerical routine used to stimulate the wave propagation processes was the discrete element method (DEM). Idealized particulate assemblies are used to model real granular materials. The DEM method uses the simplifying assumption of Newtonian rigid-body dynamics to calculate the translational and rotational motion of each particle in these model assemblies. A new normal contact law governing particle interactions through a fluid was developed based on the theory of elastohydrodynamics. Tangential interactions were accounted for by using a simple shearing approximation and a Coulomb law.

Using these new contact laws, simulations of one- and two-dimensional model assemblies were performed. Specific results for wave speed and amplitude attenuation are presented, and relationships are established between the microstructure or fabric of particulate materials and its macroscopic wave propagation behaviors. Results include the effects of particle size, wavelength, viscosity, interparticle gap spacing, etc. on dynamic load transfers in porous media.

It was observed that the presence of pore fluid can have significant effects on the macroscopic dynamic behaviors of particulate materials by changing the contact response between adjacent particles through hydrodynamic squeeze-film action. Wave attenuation increases and wave velocity decreases with increasing interparticle gap spacing, and these effects are more pronounced at smaller inter particle gap spacing. It was found that there was a slight increase in wave velocity with increasing pore fluid viscosity. Wave velocity was found to be higher through assemblies of stiffer particles. It also can be concluded that wave propagational behaviors of particulate materials are directly related to the microstructure or fabric of them.

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