Creeping granular motion under variable gravity levels

Arndt, Tim; Brucks, Antje; Ottino, Julio M.; Lueptow, Richard M.

doi:10.1103/physreve.74.031307

Cited by 22 publications

(12 citation statements)

References 24 publications

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“…The relative flowing layer time, τ fl /T , and the solid body rotation residence time, τ /T , were measured for 20 tumbler rotations. Results in Table II indicate that τ /T is slightly longer than the predicted value of 0.5 for f = 50%, probably due to a small degree of internal slip and slight rearrangement [28][29][30] of particles in the fixed bed as the tumbler rotates. τ fl /T is about an order of magnitude less than τ /T .…”

Section: Discussionmentioning

confidence: 80%

Slow axial drift in three-dimensional granular tumbler flow

et al. 2013

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Models of monodisperse particle flow in partially filled three-dimensional tumblers often assume that flow along the axis of rotation is negligible. We test this assumption, for spherical and double cone tumblers, using experiments and discrete element method simulations. Cross sections through the particle bed of a spherical tumbler show that, after a few rotations, a colored band of particles initially perpendicular to the axis of rotation deforms: particles near the surface drift toward the pole, while particles deeper in the flowing layer drift toward the equator. Tracking of mm-sized surface particles in tumblers with diameters of 814 cm shows particle axial displacements of one to two particle diameters, corresponding to axial drift that is 13% of the tumbler diameter, per pass through the flowing layer. The surface axial drift in both double cone and spherical tumblers is zero at the equator, increases moving away from the equator, and then decreases near the poles. Comparing results for the two tumbler geometries shows that wall slope causes axial drift, while drift speed increases with equatorial diameter. The dependence of axial drift on axial position for each tumbler geometry is similar when both are normalized by their respective maximum values PACS numbers: 45.70.Mg

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Section: Discussionmentioning

confidence: 80%

Slow axial drift in three-dimensional granular tumbler flow

et al. 2013

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“…In Ref. [3], the static and dynamic angles of repose are shown to be independent of the apparent gravity in the range g < g ⋆ < 25 g. The Authors also concluded that the flow layer thickness only depends on the particle size and that the apparent gravity only influences the shear rate [2]. These results are questioned in Ref.…”

Section: Introductionmentioning

confidence: 97%

“…Either, the apparent gravity g ⋆ is increased using a Large Diameter Centrifuge (LDC), see Granular material confined in rotating tumbler has been studied under various apparent gravity conditions [2][3][4]. The idea was to determine how avalanches are influenced by the gravity and to determine the role of the gravity in geomorphology of planets.…”

Section: Introductionmentioning

confidence: 99%

Influence of the gravity on the discharge of a silo

et al. 2013

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We performed a series of experiments to investigate the flow of an assembly of non-cohesive spherical grains in both high and low gravity conditions (i.e. above and under the Earth's gravity). In high gravity conditions, we studied the flow of glass beads out of a cylindrical silo and the flow of metallic beads out of a vertical Hele-Shaw rectangular silo. Both silos were loaded in one of the gondolas of the Large Diameter Centrifuge facility (located at ESTEC) in which an apparent gravity up to 20 times the Earth's gravity can be established. To simulate low gravity conditions, we submitted a horizontal monolayer of metallic beads to the centrifuge force of a small rotation device (located at University of Liege). The influences of both gravity and aperture size on the mass flow were analysed in these various conditions. For the three systems (cylindrical silo, the Hele-shaw silo and the monolayer of beads), we demonstrated that (i) the square root scaling of the gravity found by Beverloo is relevant and (ii) the critical aperture size below which the flow is jammed does not significantly increase with the apparent gravity. Moreover, we studied in more details the Hele-Shaw silo in high gravity because this configuration allowed to determine local properties of the flow at the level of the aperture. We measured the velocity profiles and the packing fraction profiles for the various aperture sizes and apparent high gravities. We demonstrate the existence of a slip length for the flow at the level of the aperture. This later fact seems to result from the geometrical configuration of the silo.

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“…An important aspect of this setup is that the shear rate is given solely by external rotation rate and the geometry. At the same time, in this geometry the local strain rate does not depend strongly on the external compression [31], unlike the inclined plane and rotation drum where gravity has a strong effect [24,32,33]. To study the effect of pressure (gravity) and particle softness, we independently vary both gravity and particle softness by two orders of magnitude.…”

Section: Introductionmentioning

confidence: 99%

The role of gravity or pressure and contact stiffness in granular rheology

et al. 2015

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The steady-state shear rheology of granular materials is investigated in slow quasistatic and inertial flows. The effect of gravity (thus the local pressure) and the often-neglected contact stiffness are the focus of this study. A series of particle simulations are performed on a weakly frictional granular assembly in a split-bottom geometry considering various magnitudes of gravity and contact stiffnesses. While traditionally the inertial number, i.e., the ratio of stress to strain-rate time scales, is used to describe the flow rheology, we report that a second dimensionless number, the ratio of softness and stress time scales, must also be included to characterize the bulk flow behavior. For slow, quasistatic flows, the density increases while the effective (macroscopic) friction decreases with increase in either particle softness or local pressure. This trend is added to the μ I ( )rheology and can be traced back to the anisotropy in the contact network, displaying a linear correlation between the effective friction coefficient and deviatoric fabric in the steady state. When the external rotation rate is increased towards the inertial regime, for a given gravity field and contact stiffness, the effective friction increases faster than linearly with the deviatoric fabric.

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Creeping granular motion under variable gravity levels

Cited by 22 publications

References 24 publications

Slow axial drift in three-dimensional granular tumbler flow

Slow axial drift in three-dimensional granular tumbler flow

Influence of the gravity on the discharge of a silo

The role of gravity or pressure and contact stiffness in granular rheology

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