Velocity profiles, stresses, and Bagnold scaling of sheared granular system in zero gravity

Baran, Oleh; Kondic, Lou

doi:10.1063/1.1951567

Cited by 13 publications

(18 citation statements)

References 44 publications

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“…The width of the distribution decays more rapidly than expected from the Cen-tral Limit Theorem (CLT) for uncorrelated forces, which is in contrast to alternative previous observations [31,32] on sheared, dynamic, and frictional particle systems.…”

Section: Discussioncontrasting

confidence: 53%

“…In our study we will therefore simplify by switching off friction and shear and, instead of varying particle size, we measure the pressure at the walls with pressure-cells of different sizes. Baran and Kondic [32], on the other hand, observed that the width of the distribution decays slower than for un-correlated forces for larger averaging times and attribute this to the absence of zero-force contacts. Their system, however, was sheared in the collisional and thus dynamic regime, unlike the quasi-static isotropically stressed situation considered in this study.…”

mentioning

confidence: 99%

“…Data on stress fluctuations in sheared systems of frictional particles were reported in Refs. [31,32]. Miller et al [31] observed that the width of the distribution was rather independent of the particle size and thus weakly dependent on the number of particles contributing to the stress measured on their pressure cell.…”

mentioning

confidence: 99%

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Force statistics and correlations in dense granular packings

Müller¹,

Luding²,

Pöschel

2010

Chemical Physics

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In dense, static, polydisperse granular media under isotropic pressure, the probability density and the correlations of particle-wall contact forces are studied.Furthermore, the probability density functions of the populations of pressures measured with different sized circular pressure cells is examined. The questions answered are: (i) What is the number of contacts that has to be considered so that the measured pressure lies within a certain error margin from its expectation value? (ii) What is the statistics of the pressure probability density as function of the size of the pressure cell? Astonishing non-random correlations between contact forces are evidenced that lead to a rapid decay of the width of the distribution and range at least 10 to 15 particle diameters. Finally, an experiment is proposed to tackle and better understand this issue.

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Section: Discussioncontrasting

confidence: 53%

mentioning

confidence: 99%

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Force statistics and correlations in dense granular packings

Müller¹,

Luding²,

Pöschel

2010

Chemical Physics

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“…The advantages of this model for the coefficient of restitution are discussed and demonstrated in Refs. [15,18,19,20,21,22]. We have set ǫ = 0.6, because this value gives the best agreement in terms of particle compaction observed in similarly agitated states in experiments with nylon balls and in our simulations.…”

Section: B System Parametersmentioning

confidence: 99%

Granular circulation in a cylindrical pan: Simulations of reversing radial and tangential flows

et al. 2007

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Granular flows due to simultaneous vertical and horizontal excitations of a flat-bottomed cylindrical pan are investigated using event-driven molecular dynamics simulations. In agreement with recent experimental results, we observe a transition from a solid-like state, to a fluidized state in which circulatory flow occurs simultaneously in the radial and tangential directions. By going beyond the range of conditions explored experimentally, we find that each of these circulations reverse their direction as a function of the control parameters of the motion. We numerically evaluate the dynamical phase diagram for this system and show, using a simple model, that the solid-fluid transition can be understood in terms of a critical value of the radial acceleration of the pan bottom; and that the circulation reversals are controlled by the phase shift relating the horizontal and vertical components of the vibrations. We also discuss the crucial role played by the geometry of the boundary conditions, and point out a relationship of the circulation observed here and the flows generated in vibratory conveyors.

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“…We note that recent experiments [5] on granular media undergoing planar cyclic shear do show slow evolution; however, further experiments are required. Similarly, simulations of frictional granular media undergoing Couette flow in 3D have reported significant time evolution of the measured velocity profiles [21]. To quantify the shape of the velocity profiles as a function of time, we define the degree of nonlinearity as…”

Section: A Time Evolution Of Velocity Profilesmentioning

confidence: 99%

Stabilization of nonlinear velocity profiles in athermal systems undergoing planar shear flow

O’Hern

Kondic

2005

Phys. Rev. E

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We perform molecular dynamics simulations of model granular systems undergoing boundarydriven planar shear flow in two spatial dimensions with the goal of developing a more complete understanding of how dense particulate systems respond to applied shear. In particular, we are interested in determining when these systems will possess linear velocity profiles and when they will develop highly localized velocity profiles in response to shear. In previous work on similar systems we showed that nonlinear velocity profiles form when the speed of the shearing boundary exceeds the speed of shear waves in the material. However, we find that nonlinear velocity profiles in these systems are unstable at very long times. The degree of nonlinearity slowly decreases in time; the velocity profiles become linear when the granular temperature and density profiles are uniform across the system at long times. We measure the time t l required for the velocity profiles to become linear and find that t l increases as a power-law with the speed of the shearing boundary and increases rapidly as the packing fraction approaches random close packing. We also performed simulations in which differences in the granular temperature across the system were maintained by vertically vibrating one of the boundaries during shear flow. We find that nonlinear velocity profiles form and are stable at long times if the difference in the granular temperature across the system exceeds a threshold value that is comparable to the glass transition temperature in an equilibrium system at the same average density. Finally, the sheared and vibrated systems form stable shear bands, or highly localized velocity profiles, when the applied shear stress is lowered below the yield stress of the static part of the system.

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Velocity profiles, stresses, and Bagnold scaling of sheared granular system in zero gravity

Cited by 13 publications

References 44 publications

Force statistics and correlations in dense granular packings

Force statistics and correlations in dense granular packings

Granular circulation in a cylindrical pan: Simulations of reversing radial and tangential flows

Stabilization of nonlinear velocity profiles in athermal systems undergoing planar shear flow

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