Two types of avalanche behaviour in model granular media (original) (raw)
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INTERNAL AVALANCHES IN MODELS OF GRANULAR MEDIA
Fractals, 1999
We study the phenomenon of internal avalanching within the context of recently introduced lattice models of granular media. The avalanche is produced by pulling out a grain at the base of the packing and studying how many grains have to rearrange before the packing is once more stable. We find that the avalanches are long-ranged, decaying as a power-law. We study the distriution of avalanches as a function of the density of the packing and find that the avalanche distribution is a very sensitive structural probe of the system.
Disorder, memory and avalanches in sandpiles
EPL (Europhysics Letters), 1994
We construct a cellular-automaton model of a sandpile with unquenched disorder. This models the behaviour of a real sandpile in which the structure is disordered and grain rearrangements cause the structure to change with time. We find that the avalanches retain a memory of the evolving disorder and do not exhibit Self-Organised Criticality. SOC is retrieved in the limit of no disorder. We construct a phase diagram, for the scaling properties, which is parametrised in terms of disorder and its rate of change and we provide a framework for the interpretation of recent theory and experiments.
Precursors and triggering mechanisms of granular avalanches
Comptes Rendus Physique, 2015
The dynamics of inclined granular packings driven towards their stability limits are studied experimentally using imaging techniques as well as acoustic methods. The formers allow to study grain rearrangements during the tilting. The implementation of both passive and active acoustic methods for probing the granular packings, with capabilities for time resolved measurements, provides information on various elastic properties of the layers along the destabilization process, including the transient precursors. Systematic experiments of granular layer destabilization for various granular media and external conditions are compared and allow to better understand the mechanisms responsible for the appearance, periodicity and intensity of precursors. La dynamique des empilements granulaires inclinés jusqu'à leur limite de stabilité peut etreétudiéeà l'aide d'expériences utilisant des techniques d'imagerie ou des méthodes acoustiques. Les premières permettent l'étude des réarrangements de grains pendant l'inclinaison. L'implémentation de méthodes acoustiques passives et actives pour le sondage d'empilements granulaires en temps réel, permet d'estimer la variation des propriétéś elastiques au cours du processus de déstabilisation, incluant le régime des précurseurs. Des expériences systématiques de déstabilisation de couches granulaires pour divers milieux granulaires et conditions extérieures sont comparées et permettent d'avoir une meilleure compréhension des mécanismes responsables de l'apparition, de la périodicité et de l'intensité des précurseurs.
Lattice-gas model of avalanches in a granular pile
Physical Review E, 1998
A granular media lattice gas (GMLG) model is used to study avalanches in a two-dimensional granular pile. We demonstrate the efficiency of the algorithm by showing that several features of the non-critical behaviour of real sandpile surfaces, such as the bounded outflow statistics or the finitesize effect of the time evolution of the pile mass, can be reproduced by this simulation approach.
Physical Review E, 2000
We describe the surface properties of a simple lattice model of a sandpile that includes evolving structural disorder. We present a dynamical scaling hypothesis for generic sandpile automata, and additionally explore the kinetic roughening of the sandpile surface, indicating its relationship with the sandpile evolution. Finally, we comment on the surprisingly good agreement found between this model, and a previous continuum model of sandpile dynamics, from the viewpoint of critical phenomena. 05.50.+q, 81.05.Rm Avalanches are the signatures of instabilities on an evolving surface: regions on a sandpile, for example, which protrude excessively from the surface, get dislodged by such mechanisms. This most intuitive picture of avalanching is the one we seek to model and study: although presented here in the context of sandpiles, a similar picture may be relevant to intermittent granular flows along an inclined plane , or to sediment consolidation . As deposition occurs on a sandpile surface, clusters of grains grow unevenly at different positions and roughness builds up until further deposition renders some of the clusters unstable. These then start 'toppling', so that grains from an already unstable cluster flow down the sandpile, knocking off grains from other similar clusters which they encounter. The net effect of this is to 'wipe off' protrusions (where there is a surfeit of grains at a cluster) and to 'fill in' dips, where the oncoming avalanche can disburse some of its grains. In short, the surface is smoothed by the passage of the avalanche so that there is a rough precursor surface, and a smoothed post-avalanche surface.
Avalanches and ripples in sandpiles
Modelling Critical and Catastrophic Phenomena in …, 2006
In this paper we unify several approaches taken to model sandpile dynamics, with a focus on avalanches and ripples. Our approaches include a coupled-map lattice model of sand in a rotating cylinder as well as noisy coupled nonlinear equations to model sandpile dynamics and ripple formation.
Development of correlations in the dynamics of wet granular avalanches
Physical review. E, Statistical, nonlinear, and soft matter physics, 2003
A detailed characterization of avalanche dynamics of wet granular media in a rotating drum apparatus is presented. The results confirm the existence of the three wetness regimes observed previously: the granular, the correlated, and the viscoplastic regime. These regimes show qualitatively different dynamic behaviors that are reflected in all the investigated quantities. We discuss the effect of interstitial liquid on the characteristic angles of the material and on the avalanche size distribution. These data also reveal logarithmic aging and allow us to map out the phase diagram of the dynamic behavior as a function of liquid content and flow rate. Via quantitative measurements of the flow velocity and the granular flux during avalanches, we characterize avalanche types unique to wet media. We also explore the details of viscoplastic flow (observed at the highest liquid contents) in which there are lasting contacts during flow, leading to coherence across the entire sample. This co...
Porous Effects in the Description of the Dynamics of Granular Avalanches
Solid Mechanics and Its Applications, 2005
Granular mixtures are porous media of immense importance in geophysical and industrial applications. Snow avalanches, debris-and mud-flows, landslides and rockslides are examples of rapid flows of geomaterials whereas flows of fine granular materials in silos, hoppers, rotating drums and heap formations are examples from process engineering. In order to understand these phenomena properly, one needs physical-mathematical descriptions including appropriate constitutive relations and suitable numerical simulations. We present recently developed model equations by Pudasaini & Hutter for free gravity-driven flows of a single phase dry granular material down complicated real mountain terrains generated by arbitrary space curves with slowly varying curvature and torsion. These are very important extensions to the successful Savage-Hutter (SH) theory. Because of the density preserving assumption the effect of the porosity can only be accounted for in the closure statements. This is done here and its consequences are illustrated. Shock-capturing numerical schemes are used to integrate the model hyperbolic conservation system of equations in order to control spurious jumps in the mapping of the descending masses. The physical significance of the numerical simulations is discussed.
Avalanche Dynamics in Wet Granular Materials
Physical Review Letters, 2002
We have studied the dynamics of avalanching wet granular media in a rotating drum apparatus. Quantitative measurements of the flow velocity and the granular flux during avalanches allow us to characterize novel avalanche types unique to wet media. We also explore the details of viscoplastic flow (observed at the highest liquid contents) in which there are lasting contacts during flow, leading to coherence across the entire sample. This coherence leads to a velocity-independent flow depth at high rotation rates and novel robust pattern formation in the granular surface.
From waves to avalanches: two different mechanisms of sandpile dynamics
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 2000
Time series resulting from wave decomposition show the existence of different correlation patterns for avalanche dynamics. For the d=2 Bak-Tang-Wisenfeld model, long range correlations determine a modification of the wave size distribution under coarse graining in time, and multifractal scaling for avalanches. In the Manna model, the distribution of avalanche coincides with that of waves, which are uncorrelated and obey finite size scaling, a result expected also for the d=3 Bak-Tang-Wiesenfeld sandpile.