Compaction of anisotropic granular materials: Experiments and simulations (original) (raw)

Adsorption-desorption model and its application to vibrated granular materials

Physical Review E, 2000

We investigate both analytically and by numerical simulation the kinetics of a microscopic model of hard rods adsorbing on a linear substrate, a model which is relevant for compaction of granular materials. The computer simulations use an event-driven algorithm which is particularly efficient at very long times. For a small, but finite desorption rate, the system reaches an equilibrium state very slowly, and the long-time kinetics display three successive regimes: an algebraic one where the density varies as 1/t, a logarithmic one where the density varies as 1/ ln(t), followed by a terminal exponential approach. The characteristic relaxation time of the final regime, though incorrectly predicted by a mean field arguments, can be obtained with a systematic gap-distribution approach. The density fluctuations at equilibrium are also investigated, and the associated time-dependent correlation function exhibits a power law regime followed by a final exponential decay. Finally, we show that denser particle packings can be obtained by varying the desorption rate during the process.

Experimental compaction of anisotropic granular media

The European Physical Journal E, 2005

We report on experiments to measure the temporal and spatial evolution of packing arrangements of anisotropic and weakly confined granular material, using high-resolution γ-ray adsorption. In these experiments, the particle configurations start from an initially disordered, low-packing-fraction state and under vertical solicitations evolve to a dense state. We find that the packing fraction evolution is slowed by the grain anisotropy but, as for spherically shaped grains, can be well fitted by a stretched exponential. For a given type of grains, the characteristic times of relaxation and of convection are found to be of the same order of magnitude. On the contrary compaction mechanisms in the media strongly depend on the grain anisotropy.

Microscopic two-dimensional lattice model of dimer granular compaction with friction

2002

We study by Monte Carlo simulation the compaction dynamics of hard dimers in 2D under the action of gravity, subjected to vertical and horizontal shaking, considering also the case in which a friction force acts for horizontal displacements of the dimers. These forces are modeled by introducing effective probabilities for all kinds of moves of the particles. We analyze the dynamics for different values of the time τ during which the shaking is applied to the system and for different intensities of the forces. It turns out that the density evolution in time follows a stretched exponential behavior if τ is not very large, while a power law tail develops for larger values of τ . Moreover, in the absence of friction, a critical value τ * exists which signals the crossover between two different regimes: for τ < τ * the asymptotic density scales with a power law of τ , while for τ > τ * it reaches logarithmically a maximal saturation value. Such behavior smears out when a finite friction force is present. In this situation the dynamics is slower and lower asymptotic densities are attained. In particular, for significant friction forces, the final density decreases linearly with the friction coefficient. We also compare the frictionless single tap dynamics to the sequential tapping dynamics, observing in the latter case an inverse logarithmic behavior of the density evolution, as found in the experiments.

Simple model with facilitated dynamics for granular compaction

Physical Review E, 1999

A simple lattice model is used to study compaction in granular media. As in real experiments, we consider a series of taps separated by large enough waiting times. The relaxation of the density exhibits the characteristic inverse logarithmic law. Moreover, we have been able to identify analytically the relevant time scale, leading to a relaxation law independent of the specific values of the parameters. Also, an expression for the asymptotic density reached in the compaction process has been derived. The theoretical predictions agree fairly well with the results from the Monte Carlo simulation.

A microscopic 2D lattice model of dimer granular compaction with friction

Physical Review E, 2002

We study by Monte Carlo simulation the compaction dynamics of hard dimers in 2D under the action of gravity, subjected to vertical and horizontal shaking, considering also the case in which a friction force acts for horizontal displacements of the dimers. These forces are modeled by introducing effective probabilities for all kinds of moves of the particles. We analyze the

Why shape matters in granular compaction

Journal of Physics A: Mathematical and …, 2003

We present a stochastic model of dynamically interacting grains in one dimension, in the presence of a low vibrational intensity, to investigate the effect of shape on the statics and dynamics of the compaction process. Regularity and irregularity in grain shapes are shown to be centrally important in determining the statics of close-packing states, as well as the nature of zero-and low-temperature dynamics in this columnar model.

Self-Structuring of Granular Media under Internal Avalanching

Physical Review Letters, 1999

We study the phenomenon of internal avalanching within the context of recently proposed "Tetris" lattice models for granular media. We define a recycling dynamics under which the system reaches a steady state which is self-structured, i.e. it shows a complex interplay between textured internal structures and critical avalanche behavior. Furthermore we develop a general mean-field theory for this class of systems and discuss possible scenarios for the breakdown of universality.

Simulation of Granular Compacts in two dimensions

Granular Matter, 2001

Simulations of granular packings in 2-D by throw-any technological or industritd application. Her% we"will .:, ing dEl& ih a rectangular die are performed. Diiferent size ., distributions as bimodal, uniform and gauasian are used. Once the array of particles is done, a relaxation process is carried on using a large-amplitude, low-frequency vertical shaking. This relaxation is performed a number N of times. Then, we measure the density of the package, con-t act distribution, coordination number distribution, entropy md also the' disks size distribution vs. height. The dependence of all these magnitudes on the number N of "shakings" used to relax the packing and on the size distrihution. parameters are explored and discussed.

Compaction of granular systems

World Scientific Lecture Notes in Complex Systems, 2007

When submitted to gentle mechanical taps, a granular packing slowly compacts until it reaches a stationary state that depends on the tap characteristics. This phenomenon, granular compaction, reveals part of the complex nature of granular dynamics. Here, we recall some experimental results on granular compaction and show that, under certain circumstances, order appears in these systems. Investigations on that crystallization are reported.