Plug flow and the breakdown of Bagnold scaling in cohesive granular flows

Brewster, Robert C.; Grest, Gary S.; Landry, James W.; Levine, Alex

doi:10.1103/physreve.72.061301

Cited by 55 publications

(40 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We adopt the history-dependent shear contact model initially developed by Cundall and Strack [15]. This well-tested model has been used by many others to model the dynamics of granular assemblies [14,[16][17][18][19][20][21][22][23][24]. The essence of this model is to keep track of the elastic shear displacement of two particles throughout the lifetime of their contact, and applying the Coulomb elastic yield criterion when the displacement reaches a critical value.…”

Section: Grain-grain Interactionmentioning

confidence: 99%

Deformation-driven diffusion and plastic flow in amorphous granular pillars

Rieser

Liu

et al. 2015

Phys. Rev. E

View full text Add to dashboard Cite

We report a combined experimental and simulation study of deformation-induced diffusion in compacted quasitwo-dimensional amorphous granular pillars, in which thermal fluctuations play a negligible role. The pillars, consisting of bidisperse cylindrical acetal plastic particles standing upright on a substrate, are deformed uniaxially and quasistatically by a rigid bar moving at a constant speed. The plastic flow and particle rearrangements in the pillars are characterized by computing the best-fit affine transformation strain and nonaffine displacement associated with each particle between two stages of deformation. The nonaffine displacement exhibits exponential crossover from ballistic to diffusive behavior with respect to the cumulative deviatoric strain, indicating that in athermal granular packings, the cumulative deviatoric strain plays the role of time in thermal systems and drives effective particle diffusion. We further study the size-dependent deformation of the granular pillars by simulation, and find that different-sized pillars follow self-similar shape evolution during deformation. In addition, the yield stress of the pillars increases linearly with pillar size. Formation of transient shear lines in the pillars during deformation becomes more evident as pillar size increases. The width of these elementary shear bands is about twice the diameter of a particle, and does not vary with pillar size.

show abstract

Section: Grain-grain Interactionmentioning

confidence: 99%

Deformation-driven diffusion and plastic flow in amorphous granular pillars

Rieser

Liu

et al. 2015

Phys. Rev. E

View full text Add to dashboard Cite

show abstract

“…We quantify the size of these networks by measuring correlations between grain forces and find that there are dramatic changes in the statistics of contact forces as the size of the networks increases. Interactions in realistic granular materials arise due to grain elasticity and friction, but are complicated by various other mechanisms including humidity [5,6,7,8,9], grain shapes [10,11,12], and fracture processes occurring within the material [13]. However, a great deal of theoretical and computational progress has been made using the simple approximation that grains are spherical and perfectly dry [14].…”

Section: Introductionmentioning

confidence: 99%

Spatial force correlations in granular shear flow. I. Numerical evidence

2007

View full text Add to dashboard Cite

We investigate the emergence of long-range correlations in granular shear flow. By increasing the density of a simulated granular flow we observe a spontaneous transition from a dilute regime, where interactions are dominated by binary collisions, to a dense regime characterized by large force networks and collective motions. With increasing density, interacting grains tend to form networks of simultaneous contacts due to the dissipative nature of collisions. We quantify the size of these networks by measuring correlations between grain forces and find that there are dramatic changes in the statistics of contact forces as the size of the networks increases. Interactions in realistic granular materials arise due to grain elasticity and friction, but are complicated by various other mechanisms including humidity [5,6,7,8,9], grain shapes [10,11,12], and fracture processes occurring within the material [13]. However, a great deal of theoretical and computational progress has been made using the simple approximation that grains are spherical and perfectly dry [14]. In this case a purely repulsive force arises when two grains come into contact due to the deformation of grains and friction between grains.Understanding the nature of grain forces and dynamics, even in this relatively simple case, has proven difficult. At very low densities it can safely be assumed that only binary interactions occur and constitutive relations can be determined by statistically tracking the repulsive force created in each interaction. This is the basis of kinetic theory, which has been successfully applied to granular flows [15,16]. However, for very large densities, it is observed that multi-grain contacts always occur [17,18,19] and contact forces are transmitted through "force chain networks" formed by the topology of the contact network [14,21,22,23]. For these high densities the forces between contacting grains still arise from grain deformation and friction, but the extent of the interactions is not localized and depends on properties of the force chain networks.The presence of force chain networks calls into question theories that assume localized interactions and has inspired new models based on properties of the force chains [24,25,26,27,28,29,30]. However, although force networks can be visualized, it has proven difficult to measure quantitative correlations between contact forces [31,32,33,34]. This has led to the speculation that force chain networks are simply a perceived correlation, until recently when long-range correlations were measured between the averaged contact forces in a quasi-static

show abstract

“…This simulation code is welldeveloped and has been used by many authors over a number of years [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. It employs a modified version of a contact model originally employed by Cundall and Strack [33] for the simulation of cohesionless particulates, featuring a normal elastic interaction, viscoelastic terms, history-dependent tangential forces and a Coulomb friction criterion.…”

Section: Introductionmentioning

confidence: 99%

Physical test of a particle simulation model in a sheared granular system

2009

View full text Add to dashboard Cite

We report a detailed comparison of a slow gravity driven sheared granular flow with a computational model performed with the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). To our knowledge, this is the first thorough test of the LAMMPS model with a laboratory granular flow. In the experiments, grains flow inside a silo with a rectangular cross-section, and are sheared by a rough boundary on one side and smooth boundaries on the other sides. Individual grain position and motion are measured using a particle index matching imaging technique where a fluorescent dye is added to the interstitial liquid which has the same refractive index as the glass beads. The boundary imposes a packing order, and the grains are observed to flow in layers which get progressively more disordered with distance from the walls. The computations use a Cundall-Strack contact model between the grains, using contact parameters that have been used in many other previous studies, and ignore the hydrodynamic effects of the interstitial liquid. Computations are performed to understand the effect of particle coefficient of friction, elasticity, contact model, and polydispersity on mean flow properties. After appropriate scaling, we find that the mean velocity of the grains and the number density as a function of flow cross-section observed in the experiments and the simulations are in excellent agreement. The mean flow profile is observed to be unchanged over a broad range of coefficient of friction, except near the smooth wall. We show that the flow profile is not sensitive to at least 10% polydispersity in particle size. Because the grain elasticity used is smaller in the computations as compared with glass grains, wave-like features can be noted over short time scales in the mean velocity and the velocity auto-correlations measured in the simulations. These wave features occur over an intermediate timescale larger than the particle interaction but smaller than the timescale of the macroscopic flow features. The wave features become more prominent as grain elasticity is further reduced. We then perform a detailed comparison of the particle fluctuation properties as measured by the displacement probability distribution function and the mean square displacement. Excellent agreement is observed over a time interval over which particles can be tracked effectively in the experiments. Using the longer tracking intervals possible in the simulations, we find that the diffusion in the layers is greater in the flow direction, than in the perpendicular direction. Further signatures of confinement and hopping between layers is observed. All in all, our study provides strong support for the LAMMPS model of granular flow, and further supports the hypothesis that the interstitial liquid has negligible effects on granular fluctuations provided the flow is slow.

show abstract

Plug flow and the breakdown of Bagnold scaling in cohesive granular flows

Cited by 55 publications

References 30 publications

Deformation-driven diffusion and plastic flow in amorphous granular pillars

Deformation-driven diffusion and plastic flow in amorphous granular pillars

Spatial force correlations in granular shear flow. I. Numerical evidence

Physical test of a particle simulation model in a sheared granular system

Contact Info

Product

Resources

About