CiteULike: dchen's Behringer

Response to perturbations for granular flow in a hopper

John Wambaugh — 2008-06-10T18:55:24-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 5. (2007)

We experimentally investigate the response to perturbations of circular symmetry for dense granular flow inside a three-dimensional right-conical hopper. These experiments consist of particle tracking velocimetry for the flow at the outer boundary of the hopper. We are able to test commonly used constitutive relations and observe granular flow phenomena that we can model numerically. Unperturbed conical hopper flow has been described as a radial velocity field with no azimuthal component. Guided by numerical models based upon continuum descriptions, we find experimental evidence for secondary, azimuthal circulation in response to perturbation of the symmetry with respect to gravity by tilting. For small perturbations we can discriminate between constitutive relations, based upon the agreement between the numerical predictions they produce and our experimental results. We find that the secondary circulation can be suppressed as wall friction is varied, also in agreement with numerical predictions. For large tilt angles we observe the abrupt onset of circulation for parameters where circulation was previously suppressed. Finally, we observe that for large tilt angles the fluctuations in velocity grow, independent of the onset of circulation.

Stress Fluctuations in a 2D Granular Couette Experiment: A Continuous Transition

Daniel Howell — 2008-04-27T00:21:13-00:00

Physical Review Letters, Vol. 82, No. 26. (28 June 1999), 5241.

Kinematics of a two-dimensional granular Couette experiment at the transition to shearing

CT Veje — 2008-04-27T00:09:50-00:00

Physical Review E, Vol. 59, No. 1. (1 January 1999), 739.

Granular solids, liquids, and gases

Heinrich Jaeger — 2008-03-25T17:44:43-00:00

Reviews of Modern Physics, Vol. 68, No. 4. (October 1996), 1259.

Granular materials are ubiquitous in the world around us. They have properties that are different from those commonly associated with either solids; liquids; or gases. In this review the authors select some of the special properties of granular materials and describe recent research developments.[S0034-6861(96)00204-8]

Footprints in Sand: The Response of a Granular Material to Local Perturbations

Junfei Geng — 2008-04-27T00:00:46-00:00

Physical Review Letters, Vol. 87, No. 3. (2 July 2001), 035506.

Green's function measurements of force transmission in 2D granular materials

Junfei Geng — 2008-03-28T13:14:35-00:00

Physica D: Nonlinear Phenomena, Vol. 182, No. 3-4. (15 August 2003), pp. 274-303.

We describe experiments that probe the response to a point force of 2D granular systems under a variety of conditions. Using photoelastic particles to determine forces at the grain scale, we obtain ensembles of responses for the following particle types, packing geometries and conditions: monodisperse ordered hexagonal packings of disks, bidisperse packings of disks with different amounts of disorder, disks packed in a regular rectangular lattice with different frictional properties, packings of pentagonal particles, systems with forces applied at an arbitrary angle at the surface, and systems prepared with shear deformation, hence with texture or anisotropy. We experimentally show that disorder, packing structure, friction and texture significantly affect the average force response in granular systems. For packings with weak disorder, the mean forces propagate primarily along lattice directions. The width of the response along these preferred directions grows with depth, increasingly so as the disorder of the system grows. Also, as the disorder increases, the two propagation directions of the mean force merge into a single direction. The response function for the mean force in the most strongly disordered system is quantitatively consistent with an elastic description for forces applied nearly normally to a surface, but this description is not as good for non-normal applied forces. These observations are consistent with recent predictions of Bouchaud et al. [Eur. Phys. J. E 4 (2001) 451] and Socolar et al. [Eur. Phys. J. E 7 (2002) 353] and with the anisotropic elasticity models of Goldenberg and Goldhirsch [Phys. Rev. Lett. 89 (2002) 084302]. At this time, it is not possible to distinguish between these two models. The data do not support a diffusive picture, as in the q-model, and they are in conflict with data by Da Silva and Rajchenbach [Nature 406 (2000) 708] that indicate a parabolic response for a system consisting of cuboidal blocks. We also explore the spatial properties of force chains in an anisotropic textured system created by a nearly uniform shear. This system is characterized by stress chains that are strongly oriented along an angle of 45[degree sign], corresponding to the compressive direction of the shear deformation. In this case, the spatial correlation function for force has a range of only one particle size in the direction transverse to the chains, and varies as a power law in the direction of the chains, with an exponent of -0.81. The response to forces is the strongest along the direction of the force chains, as expected. Forces applied in other directions are effectively refocused towards the strong force chain direction.

Elastic energy, fluctuations and temperature for granular materials

L Kondic — 2008-04-26T22:48:36-00:00

EPL (Europhysics Letters), Vol. 67, No. 2. (2004), pp. 205-211.

We probe, using a model system, elastic and kinetic energies for sheared granular materials. For large enough P/Ey (pressure/Young's modulus) and P/rv2 (P/kinetic energy density) elastic dominates kinetic energy, and energy fluctuations become primarily elastic in nature. This regime has likely been reached in recent experiments. We consider a generalization of the granular temperature, Tg, with both kinetic and elastic terms and that changes smoothly from one regime to the other. This Tg is roughly consistent with a temperature adapted from equilibrium statistical mechanics.

Effects of surface friction on a two-dimensional granular system: Numerical model of a granular collider experiment

Meenakshi Dutt — 2008-04-26T22:47:13-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 2. (2007)

We present numerical results from a simulation of a granular collider experiment [B. Painter, M. Dutt, and R. P. Behringer, Physica D 175, 43 (2003)] using a numerical model which accounts for substrate frictional effects [M. Dutt and R. P. Behringer, Phys. Rev. E 70, 061304 (2004)]. We find the gradual birth and growth of a central cluster for the final state of the particles that depends on the system size, the substrate frictional dissipation, and the initial average kinetic energy. For systems where a central cluster is observed in the final state, the autocorrelation function C(r) of the interparticle spacing satisfies a Gaussian functional form C(r)=Ae−(r/)2. We also find that the fluctuation speed distributions adhere to a Maxwell-Boltzmann distribution for times in the vicinity of collapse. Our results strongly indicate that the principal mechanism responsible for the energy and momentum dissipation is the particle-substrate kinetic friction. Our findings reiterate the importance of considering the effects of substrate friction in particle-substrate systems, as shown by the agreement between our numerical results with experimental findings of Painter, Dutt, and Behringer.

Effects of surface friction on a two-dimensional granular system: Cooling bound system

Meenakshi Dutt — 2008-04-26T22:45:56-00:00

Physical Review E, Vol. 70, No. 6. (13 December 2004), 061304.

Comparing simulation and experiment of a 2D granular Couette shear device

M Lätzel — 2008-04-26T22:44:14-00:00

The European Physical Journal E - Soft Matter, Vol. 11, No. 4. (2003), pp. 325-333.

We present experiments along with molecular-dynamics (MD) simulations of a two-dimensional (2D) granular material in a Couette cell undergoing slow shearing. The grains are disks confined between an inner, rotating wheel and a fixed outer ring. The simulation results are compared to experimental studies and quantitative agreement is found. Tracking the positions and orientations of individual particles allows us to obtain density distributions, velocity and particle rotation rates for the system. The key issue of this paper is to show the extent to which quantitative agreement between an experiment and MD simulations is possible. Besides many differences in model details and the experiment, the qualitative features are nicely reproduced. We discuss the quantitative agreement/disagreement, give possible reasons, and outline further research perspectives.

Contact force measurements and stress-induced anisotropy in granular materials

TS Majmudar — 2005-06-23T02:21:24-00:00

Nature, Vol. 435, No. 7045., pp. 1079-1082.

Stress Fluctuations for Continuously Sheared Granular Materials

Brian Miller — 2008-03-24T22:01:06-00:00

Physical Review Letters, Vol. 77, No. 15. (7 October 1996), 3110.

Experiments on continuously sheared granular materials (glass spheres) with diameters 1.0≤ d ≤5 mm show large fluctuations in the normal stress; σ( t ). Experiments are carried out in an annular Couette geometry for rotation rates 0.003 < θ̇ < 1 rad/s. Power spectra from σ( t ); P (ω); show rate invariance in the fluctuations: θ̇ P (ω) is a function only of ω / θ̇; independent of θ̇. θ̇ P (ω) depends relatively weakly on d . The distributions of stresses ρ σ are similar to recent predictions for static arrays; but the width of ρ σ varies only weakly with d ; suggesting stronger spatial correlation effects than expected from theory.

Jamming Transition in Granular Systems

TS Majmudar — 2007-12-31T21:59:04-00:00

Physical Review Letters, Vol. 98, No. 5. (2007)

Recent simulations have predicted that near jamming for collections of spherical particles, there will be a discontinuous increase in the mean contact number Z at a critical volume fraction c. Above c, Z and the pressure P are predicted to increase as power laws in -c. In experiments using photoelastic disks we corroborate a rapid increase in Z at c and power-law behavior above c for Z and P. Specifically we find a power-law increase as a function of -c for Z-Zc with an exponent around 0.5, and for P with an exponent around 1.1. These exponents are in good agreement with simulations. We also find reasonable agreement with a recent mean-field theory for frictionless particles.