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Alenzi, Adel F. (2012) MODELING OF CONSOLIDATION AND FLOW OF GRANULAR MATERIAL UNDER VARYING CONDITIONS. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Granular materials are ubiquitous. They are widely used in many natural and man-made processes such as formation of lunar regolith, dunes and beach sand, as well as processes in pharmaceutical, chemical, and construction industries. Despite their clear industrial relevance, a fundamental understanding of most of the phenomena that involve granular materials in the chemical industry is lacking. Recently, it has been found that cyclic variation of the temperature of a granular bed can cause static particle beds to consolidate (increase their packing fraction) over time due to thermo-mechanical coupling. We employ experimental techniques and numerical simulations, using the thermal particle dynamics method (TPD), to study this phenomenon. In order to simulate many natural phenomena such as lunar regolith formation, one needs to determine a simulation depth of the bed which will yield realistic results yet be manageable computationally. Here we use penetration theory to estimate the required simulation bed height. Lateral periodic boundary conditions are used in our simulations to show that consolidation still occurs during vertical heating even in the absence of confining side walls.

Granular flows in which shearing plays a key role are prevalent in natural and industrial applications and understanding their behavior and flow characteristics is of considerable importance. Nevertheless, difficulties in making accurate experimental measurements, complexities involved in doing bulk characterization, and the non-linear nature of interparticle interactions have made development and testing of theoretical models extremely challenging. For this reason, the discrete element method (DEM) is often used as the gold standard for comparison to continuum-level theories of granular material flows. Due to the fact that this modeling approach is derived from first-principle constructs -- like contact mechanics -- its use in lieu of experimentation is reasonably wide-spread and is becoming a staple even in industrial practice. In this work, we explore various aspects of quantitative validation of DEM simulations using detailed measurements of simple, well-characterized flows that allow us to examine the effect of rough surfaces, rotational rates, collisional and frictional force models on granular flow using different devices. Experimentally, we use digital particle tracking velocimetry (DPTV) to obtain velocity, solids fractions, and granular temperature profiles. Computationally, we compare the results obtained using different contact mechanics force laws to those from experimental measurements and perform sensitivity analyses on device and particle geometry as well as material properties employed. In general, the frictional force models range from pragmatic linear techniques to rigorously more complex (nonlinear) contact mechanics inspired routines. Here, we examine both force models to compare with the experimental measurements. In addition, we examine the robustness of these observations to both particle materials properties as well as systemic variables (such as total system solids fraction).


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Alenzi, Adel
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairMcCarthy, Joseph
Committee MemberParker, Robert S.rparker@pitt.eduRPARKER
Committee MemberEnick, Robert M. rme@pitt.eduRME
Committee MemberVallejo, Luis E. vallejo@pitt.eduVALLEJO
Date: 26 September 2012
Date Type: Publication
Defense Date: 27 June 2012
Approval Date: 26 September 2012
Submission Date: 25 July 2012
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 144
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Chemical Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Particle Dynamics (PD), Thermal Particle Dynamics (TPD), DEM, Thermoelastic Contact, Granular Media, Thermal Cycling, Solid Fraction, Consolidation, Granular Flow, Shear Cell, Collisional Flow, Normal Forces, Frictional Forces.
Date Deposited: 26 Sep 2012 15:04
Last Modified: 15 Nov 2016 14:00


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