Granular Convection in Microgravity

Murdoch, Naomi; Rozitis, B.; Nordstrom, Kerstin; Green, Simon; Michel, Patrick; Lophem, T. L. de; Losert, Wolfgang

doi:10.1103/physrevlett.110.018307

Cited by 67 publications

(38 citation statements)

References 25 publications

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“…Another related issue that remains untouched is the effect of particle softness and external compression (gravity here) on the non-locality. A study of effect of pressure (gravity) on primary and secondary velocity fields, as done recently in [73,74], also deserves a further study, as well as the effect of softness and pressure on the shear banding. Looking towards the future, we are now in a position to address various important issues, such as unexpectedly high shear strength of the material at low (normal) stress or reduced gravity and a direct relation between the contact anisotropy and the shear strength of the material.…”

Section: Discussionmentioning

confidence: 90%

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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Section: Discussionmentioning

confidence: 90%

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

et al. 2015

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“…shear zone geometries [16][17][18], dilatancy and packing [19][20][21], segregation [22,23], alignment and orientational order [7,24,25], macroscopic viscosities [26,27] and secondary flows [1,28]. The latter was also reported for a slightly different Taylor-Couette geometry [29]. Wortel et al [1] described the following characteristic properties of elongated grains under shear in splitbottom containers: the material formed a heap in the central region, which reached a saturation height after some transient phase.…”

Section: Introductionmentioning

confidence: 89%

Heaping and secondary flows in sheared granular materials

et al. 2016

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Cylindrical containers with a rotating bottom disk (so-called split-bottom geometry) are well established devices to shear granular materials in a continuous way, and to generate well-defined localized shear bands in the granular bed. When material composed of shape-anisotropic grains is sheared in such a container, a secondary flow is generated that leads to the formation of a considerable heap of material near the rotation center. We demonstrate that this effect can be found not only with prolate grains, as shown in a previous study, but also for oblate particle shapes. In addition, the quantitative influence of geometric and dynamic parameters is studied systematically. It is shown that the fill height of the container has considerable influence on the time scale for heap formation, but much less effect on the heap height. Results of numerical simulations agree with the experimental findings and provide insight in the particle dynamics.

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“…Murdoch et al (2013b,c,a) used a Taylor-Couette geometry and measured both sheared and convective flows induced by the shearing. Particularly, Murdoch et al (2013b) reported the effect of gravity to the sheared granular convection. They claimed that the gravity plays an essential role to make a stiff grains network in a bulk granular matter.…”

Section: Gravity Effect To the Granular Convective Velocitymentioning

confidence: 99%

Scaling of convective velocity in a vertically vibrated granular bed

Yamada

Katsuragi

2014

Planetary and Space Science

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We experimentally study the velocity scaling of granular convection which is a possible mechanism of the regolith migration on the surface of small asteroids. In order to evaluate the contribution of granular convection to the regolith migration, the velocity of granular convection under the microgravity condition has to be revealed. Although it is hard to control the gravitational acceleration in laboratory experiments, scaling relations involving the gravitational effect can be evaluated by systematic experiments. Therefore, we perform such a systematic experiment of the vibration-induced granular convection. From the experimental data, a scaling form for the granular convective velocity is obtained. The obtained scaling form implies that the granular convective velocity can be decomposed into two characteristic velocity components: vibrational and gravitational velocities. In addition, the system size dependence is also scaled. According to the scaling form, the granular convective velocity $v$ depends on the gravitational acceleration $g$ as $v \propto g^{0.97}$ when the normalized vibrational acceleration is fixed.Comment: 16pages, 10figure

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Granular Convection in Microgravity

Cited by 67 publications

References 25 publications

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

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

Heaping and secondary flows in sheared granular materials

Scaling of convective velocity in a vertically vibrated granular bed

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