CiteULike: kdesmond's granular_flow

RAPID GRANULAR FLOWS

Isaac Goldhirsch — 2008-03-06T05:32:38-00:00

Annual Review of Fluid Mechanics, Vol. 35, No. 1. (2003), pp. 267-293.

Abstract The recent avalanche of research activity in the field of granular matter has yielded much progress. The use of state-of-the-art (and other) computational and experimental methods has led to the discovery of new states and patterns and enabled detailed tests of theories and models. The application of statistical mechanical methods and phenomenology has contributed to the understanding of the microscopic a nd macroscopic properties of granular systems. Some previously open problems seem to be solved. Fluidized granular systems (rapid granular flows), recently referred to as granular gases, are often modeled by hydrodynamic equations of motion, some of which are based on systematic expansions applied to the pertinent Boltzmann equation. The undeniable success of granular hydrodynamics is somewhat surprising in view of the lack of scale separation in these systems and the neglect of certain correlations in most derivations of the hydrodynamic equations. Microstructures have been recognized as key features of granular gases; explanations for their existence have been proposed, and many of their properties elucidated. Granular-gas multistability can often be traced back to microstructure dynamics. In spite of these and other impressive advances, this field still poses serious challenges.

Compaction force in a confined granular column

D Arroyo-Cetto — 2008-05-03T00:02:33-00:00

Physical Review E, Vol. 68, No. 5. (7 November 2003), 051301.

Flows of Dense Granular Media

Yoel Forterre — 2008-03-06T05:28:36-00:00

Annual Review of Fluid Mechanics, Vol. 40, No. 1. (2008), pp. 1-24.

We review flows of dense cohesionless granular materials, with a special focus on the question of constitutive equations. We first discuss the existence of a dense flow regime characterized by enduring contacts. We then emphasize that dimensional analysis strongly constrains the relation between stresses and shear rates, and show that results from experiments and simulations in different configurations support a description in terms of a frictional visco-plastic constitutive law. We then discuss the successes and limitations of this empirical rheology in light of recent alternative theoretical approaches. Finally, we briefly present depth-averaged methods developed for free surface granular flows.

Scaling vertical drag forces in granular media

G Hill — 2008-05-02T23:58:00-00:00

EPL (Europhysics Letters), Vol. 72, No. 1. (2005), pp. 137-143.

The average drag forces on intruders slowly plunging into and withdrawing from shallow beds of monodisperse smooth glass beads and of sifted rough sand scale with the immersion depth and lateral dimensions of the intruder. The withdrawal forces are comparable for both types of media; however, the plunging forces for sand are substantially greater than for smooth glass beads. Furthermore, for glass beads, the rescaled plunging and withdrawal forces have two different power law dependences on the immersion depth, with exponents greater than unity.

Rheophysics of dense granular materials: Discrete simulation of plane shear flows

Frédéric da Cruz — 2008-05-02T23:57:00-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 72, No. 2. (2005)

We study the plane shear flow of a dense assembly of dissipative disks using discrete simulation and prescribing the pressure and the shear rate. Those shear states are steady and uniform, and become intermittent in the quasistatic regime. In the limit of rigid grains, the shear state is determined by a single dimensionless number, called the inertial number I, which describes the ratio of inertial to pressure forces. Small values of I correspond to the quasistatic critical state of soil mechanics, while large values of I correspond to the fully collisional regime of kinetic theory. When I increases in the intermediate dense flow regime, we measure an approximately linear decrease of the solid fraction from the maximum packing value, and an approximately linear increase of the effective friction coefficient from the static internal friction value. From those dilatancy and friction laws, we deduce the constitutive law for dense granular flows, with a plastic Coulomb term and a viscous Bagnold term. The mechanical characteristics of the grains (restitution, friction, and elasticity) have a small influence in the dense flow regime. Finally, we show that the evolution of the relative velocity fluctuations and of the contact force anisotropy as a function of I provides a simple explanation of the friction law.

Probing creep motion in granular materials with light scattering

Linda Djaoui — 2008-05-02T23:12:19-00:00

Granular Matter, Vol. 7, No. 4. (11 November 2005), pp. 185-190.

We describe a dynamic light scattering experiment designed in order to study creep motion in granular materials. This method is based on the recording of the speckle pattern with a charge coupled device (CCD) camera. The autocorrelation function of the scattered electric field is calculated and related to the displacement field of the beads. As an application, the measurement of the thermal expansion of a granular material subjected to temperature variations is presented.

Flow of dense granular material: towards simple constitutive laws

O Pouliquen — 2006-08-01T00:34:07-00:00

J. Stat. Mech., Vol. 2006, No. 07. (July 2006), P07020.

Dense flows of dry granular material

Olivier Pouliquen — 2008-05-02T23:02:34-00:00

Comptes Rendus Physique, Vol. 3, No. 2. (2002), pp. 163-175.

The behavior of dense assemblies of dry grains submitted to continuous shear deformation is still not well understood. Recently it has been the subject of several experiments and discrete particle simulations. For both confined and free surface geometries, we present the general features of such flows as well as grain-level information. We then describe the main rheological models and their predictions. To cite this article: O. Pouliquen, F. Chevoir, C. R. Physique 3 (2002) 163-175.

On dense granular flows

GDR Midi — 2008-05-02T21:47:15-00:00

The European Physical Journal E - Soft Matter, Vol. 14, No. 4. (2004), pp. 341-365.

The behaviour of dense assemblies of dry grains submitted to continuous shear deformation has been the subject of many experiments and discrete particle simulations. This paper is a collective work carried out among the French research group Groupement de Recherche Milieux Divisés (GDR MiDi). It proceeds from the collection of results on steady uniform granular flows obtained by different groups in six different geometries both in experiments and numerical works. The goal is to achieve a coherent presentation of the relevant quantities to be measured i.e. flowing thresholds, kinematic profiles, effective friction, etc. First, a quantitative comparison between data coming from different experiments in the same geometry identifies the robust features in each case. Second, a transverse analysis of the data across the different configurations, allows us to identify the relevant dimensionless parameters, the different flow regimes and to propose simple interpretations. The present work, more than a simple juxtaposition of results, demonstrates the richness of granular flows and underlines the open problem of defining a single rheology.

A constitutive law for dense granular flows

Pierre Jop — 2006-06-07T20:26:31-00:00

Nature, Vol. 441, No. 7094. (June 2006), pp. 727-730.

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

Robert Brewster — 2008-02-24T06:46:02-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 72, No. 6. (2005)

Cohesive granular media flowing down an inclined plane are studied by discrete element simulations. Previous work on cohesionless granular media demonstrated that within the steady flow regime where gravitational energy is balanced by dissipation arising from intergrain forces, the velocity profile in the flow direction scales with depth in a manner consistent with the predictions of Bagnold. Here we demonstrate that this Bagnold scaling does not hold for the analogous steady flows in cohesive granular media. We develop a generalization of the Bagnold constitutive relation to account for our observation and speculate as to the underlying physical mechanisms responsible for the different constitutive laws for cohesive and noncohesive granular media.

Rheology and Contact Lifetimes in Dense Granular Flows

Leonardo Silbert — 2008-02-24T06:45:24-00:00

Physical Review Letters, Vol. 99, No. 6. (2007)

We study the rheology and distribution of interparticle contact lifetimes for gravity-driven, dense granular flows of noncohesive particles down an inclined plane using large-scale, three dimensional, granular dynamics simulations. Rather than observing a large number of long-lived contacts as might be expected for dense flows, brief binary collisions predominate. In the hard-particle limit, the rheology conforms to Bagnold scaling, where the shear stress is quadratic in the strain rate. As the particles are made softer, however, we find significant deviations from Bagnold rheology; the material flows more like a viscous fluid. We attribute this change in the collective rheology of the material to subtle changes in the contact lifetime distribution involving the increasing lifetime and number of the long-lived contacts in the softer particle systems.

Signatures of granular microstructure in dense shear flows

Daniel Mueth — 2008-02-15T02:49:13-00:00

Nature, Vol. 406 (27 July 2000), pp. 385-389.

Granular materials and ordinary fluids react differently to shear stresses. Rather than deforming uniformly, materials such as dry sand or cohesionless powders develop shear bands1, 2, 3, 4, 5—narrow zones of large relative particle motion, with essentially rigid adjacent regions. Because shear bands mark areas of flow, material failure and energy dissipation, they are important in many industrial, civil engineering and geophysical processes6. They are also relevant to lubricating fluids confined to ultrathin molecular layers7. However, detailed three-dimensional information on motion within a shear band, including the degree of particle rotation and interparticle slip, is lacking. Similarly, very little is known about how the microstructure of individual grains affects movement in densely packed material5. Here we combine magnetic resonance imaging, X-ray tomography and high-speed-video particle tracking to obtain the local steady-state particle velocity, rotation and packing density for shear flow in a three-dimensional Couette geometry. We find that key characteristics of the granular microstructure determine the shape of the velocity profile.

Shocks in sand flowing in a silo

Azadeh Samadani — 2008-01-23T19:16:38-00:00

Journal of Fluid Mechanics, Vol. 452 (2002), pp. 293-301.

We study the formation of shocks on the surface of a granular material draining through an orifice at the bottom of a quasi-two-dimensional silo. At high flow rates, the surface is observed to deviate strongly from a smooth linear inclined profile, giving way to a sharp discontinuity in the height of the surface near the bottom of the incline, the typical response of a choking flow such as encountered in a hydraulic jump in a Newtonian fluid like water. We present experimental results that characterize the conditions for the existence of such a jump, describe its structure and give an explanation for its occurrence.

Diffusion and Mixing in Gravity-Driven Dense Granular Flows

Jaehyuk Choi — 2008-01-23T19:08:39-00:00

Physical Review Letters, Vol. 92, No. 17. (27 April 2004), 174301.

We study the transport properties of particles draining from a silo using imaging and direct particle tracking. The particle displacements show a universal transition from superdiffusion to normal diffusion; as a function of the distance fallen; independent of the flow speed. In the superdiffusive (but sub-ballistic) regime; which occurs before a particle falls through its diameter; the displacements have fat-tailed and anisotropic distributions. In the diffusive regime; we observe very slow cage breaking and Péclet numbers of order 100; contrary to the only previous microscopic model (based on diffusing voids). Overall; our experiments show that diffusion and mixing are dominated by geometry; consistent with long-lasting contacts but not thermal collisions; as in normal fluids.

Lubrication effects on the flow of wet granular materials

Qing Xu — 2008-01-23T19:06:56-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 3. (2007)

We investigate the dynamics of a partially saturated grain-liquid mixture with a rotating drum apparatus. The drum is partially filled with the mixture and then rotated about its horizontal axis. We focus on the continuous avalanching regime and measure the impact of the volume fraction and viscosity of the liquid on the dynamic surface angle. The inclination angle of the surface is observed to increase sharply to a peak and then decrease as a function of liquid volume fraction. The height of the peak is observed to increase with rotation rate. For higher liquid volume fractions, the inclination angle of the surface can decrease with viscosity before increasing. The viscosity where the minimum occurs decreases with the rotation rate of the drum. Limited measurements of the flow depth were made, and these were observed to show only fractional changes with volume fraction and rotation speeds. We show that the qualitative features of our observations can be understood by analyzing the effect of lubrication forces on the time scale over which particles come in contact.