Date of Award

Fall 1-31-2014

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering - (M.S.)

Department

Mechanical and Industrial Engineering

First Advisor

Anthony D. Rosato

Second Advisor

Pushpendra Singh

Third Advisor

Shawn Alexander Chester

Fourth Advisor

David James Horntrop

Abstract

Granular systems are widely present in the world. Soil, pharmaceutical pills, and silos filled with grain all are examples of granular systems. Experiments have long established an empirical understanding of granular systems, but an analytical understanding has been much more difficult to establish. One of the behaviors of a granular system that is well documented but poorly understood is the change in density the system undergoes when excited, also known as the densification process.

This thesis investigates the densification process of a tapped granular system using Discrete Element Model (DEM) simulations. Contact interactions in the simulations obey a well-established inelastic soft-sphere model. The computational volume consists of a rectangular parallelepiped with a square base that is 12 particle diameters wide and filled with 3456 spheres. A focus of this work is on understanding the influence of the walls on the densification process.

Several systems are observed to stay in a metastable state for thousands of taps before further densification occurs. In addition, bulk lateral movement or drift of the sphere assembly is detected after evolving to maximally dense state, even though the particles come to a complete rest between taps. Simulations conducted with solid lateral walls suggest a reduced rate of densification as compared to the periodic systems, which is hypothesized to be caused in part by a motion restriction of the spheres imposed by the solid walls.

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