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1.
The connection between granular gases and sticky gases has recently been considered, leading to the conjecture that inelastic
collapse is avoided for space dimensions higher than 4. We report Molecular Dynamics simulations of hard inelastic spheres
in dimensions 4, 5 and 6. The evolution of the granular medium is monitored throughout the cooling process. The behaviour
is found to be very similar to that of a two-dimensional system, with a shearing-like instability of the velocity field and
inelastic collapse when collisions are inelastic enough, showing that the connection with sticky gases needs to be revised.
Received 17 April 2000 and Received in final form 7 June 2000 相似文献
2.
Magneto-vibratory separation of glass and bronze granular mixtures immersed in a paramagnetic liquid
López-Alcaraz P Catherall AT Hill RJ Leaper MC Swift MR King PJ 《The European physical journal. E, Soft matter》2007,24(2):145-156
A fluid-immersed granular mixture may spontaneously separate when subjected to vertical vibration, separation occurring when
the ratio of particle inertia to fluid drag is sufficiently different between the component species of the mixture. Here,
we describe how fluid-driven separation is influenced by magneto-Archimedes buoyancy, the additional buoyancy force experienced
by a body immersed in a paramagnetic fluid when a strong inhomogeneous magnetic field is applied. In our experiments glass
and bronze mixtures immersed in paramagnetic aqueous solutions of MnCl2 have been subjected to sinusoidal vertical vibration. In the absence of a magnetic field the separation is similar to that
observed when the interstitial fluid is water. However, at modest applied magnetic fields, magneto-Archimedes buoyancy may
balance the inertia/fluid-drag separation mechanism, or it may dominate the separation process. We identify the vibratory
and magnetic conditions for four granular configurations, each having distinctive granular convection. Abrupt transitions
between these states occur at well-defined values of the magnetic and vibrational parameters. In order to gain insight into
the dynamics of the separation process we use computer simulations based on solutions of the Navier-Stokes' equations. The
simulations reproduce the experimental results revealing the important role of convection and gap formation in the stability
of the different states. 相似文献
3.
We analyze the deviations from Maxwell-Boltzmann statistics found in recent experiments studying velocity distributions in
two-dimensional granular gases driven into a non-equilibrium stationary state by a strong vertical vibration. We show that
in its simplest version, the “stochastic thermostat” model of heated inelastic hard spheres, contrary to what has been hitherto
stated, is incompatible with the experimental data, although predicting a reminiscent high-velocity stretched-exponential
behavior with an exponent 3/2. The experimental observations lead to refine a recently proposed random restitution coefficient
model. Very good agreement is then found with experimental velocity distributions within this framework, which appears self-consistent
and further provides relevant probes to investigate the universality of the velocity statistics.
Received: 27 May 2002 / Accepted: 6 May 2003 / Published online: 27 May 2003
RID="a"
ID="a"e-mail: Alain.Barrat@th.u-psud.fr 相似文献
4.
A.E. Kobryn M.V. Tokarchuk Y.A. Humenyuk 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(3):579-583
The Enskog-Landau kinetic equation is considered to describe non-equilibrium processes of a mixture of charged hard spheres.
This equation has been obtained in our previous papers by means of the non-equilibrium statistical operator method. The normal
solution of this kinetic equation found in the first approximation using the standard Chapman-Enskog method is given. On the
basis of the found solution the flows and transport coefficients have been calculated. All transport coefficients for multicomponent
mixture of spherical Coulomb particles are presented analytically for the first time. Numerical calculations of thermal conductivity
and thermal diffusion coefficient are performed for some specific mixtures of noble gases of high density. We compare the
calculations with those ones for point-like neutral and charged particles.
Received 10 June 1999 and Received in final form 15 October 1999 相似文献
5.
G.G.M. Coppa A. D'Angola 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(4):533-539
The paper deals with the stationary distribution of charged particles moving in a material medium, having scattering and absorption
properties, in which a uniform electric field is present. The purpose of the work is finding analytical solutions in simplified
but physically significant situations and comparing different approximations based on a spherical-harmonics expansion of the
velocity distribution.
Received: 28 July 1998 相似文献
6.
Z. M. Jakšić S. B. Vrhovac B. M. Panić Z. Nikolić B. M. Jelenković 《The European physical journal. E, Soft matter》2008,27(4):345-356
We study experimentally the creeping penetration of guest (percolating) grains through densely packed granular media in two dimensions. The evolution of the system of the guest grains during the penetration is studied by image analysis. To quantify the changes in the internal structure of the packing, we use Voronoï tessellation and a certain shape factor which is a clear indicator of the presence of different underlying substructures (domains). We first consider the impact of the effective gravitational acceleration on upward penetration of grains. It is found that the higher effective gravity increases the resistance to upward penetration and enhances structural organization in the system of the percolating grains. We also focus our attention on the dependence of the structural rearrangements of percolating grains on some parameters like polydispersity and the initial packing fraction of the host granular system. It is found that the anisotropy of penetration is larger in the monodisperse case than in the bidisperse one, for the same value of the packing fraction of the host medium. Compaction of initial host granular packing also increases anisotropy of penetration of guest grains. When a binary mixture of large and small guest grains is penetrated into the host granular medium, we observe size segregation patterns. 相似文献
7.
Goujon C Dalloz-Dubrujeaud B Thomas N 《The European physical journal. E, Soft matter》2007,23(2):199-215
Experiments were performed to provide insight into the
flow behavior and structure of bimodal mixtures of grains in
gravity-driven, free-surface flows. Unsteady unconfined flows
were produced by releasing instantaneously a dry granular mass,
composed of two particle sizes, over a rough inclined plane. As a
result of size segregation, the small particles are found at the
bottom of the flow and final deposit, the large particles are
found at the free surface, but also on the lateral borders and at
the front of the flow. The lateral and vertical inhomogeneous
repartitions of particles lead to two main effects that are
completely absent in monodispersed flows. The outline effect
results from the accumulation of large beads on the periphery of
the flow depending on the value of the relative friction of each
particle species on the plane. This effect in turn causes a
narrowing of the flow and/or an increase of length of the final
deposit. The interface effect results of the interaction between
layers of different size particles and causes the modification of
the thickness of the deposit. These effects occur simultaneously
and their combination leads to a great variety of behaviors. In
this investigation, evidence of the diversity of behaviors is
presented as the size ratio, relative friction and concentration
of each particle species are varied. 相似文献
8.
A. Rossani A. M. Scarfone 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):295-298
Test particles interact with a medium by means of a
bimolecular reversible chemical reaction. Two species are assumed to
be much more numerous so that they are distributed according to
fixed distributions: Maxwellians and Dirac's deltas. Equilibrium and
its stability are investigated in the first case. For the second
case, a system is constructed, in view of an approximate solution. 相似文献
9.
É. Falcon S. Fauve C. Laroche 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):183-186
We report experimental results on the behavior of an ensemble of inelastically colliding particles, excited by a vibrated
piston in a vertical cylinder. When the particle number is increased, we observe a transition from a regime where the particles
have erratic motions (“granular gas”) to a collective behavior where all the particles bounce like a nearly solid body. In
the gas-like regime, we measure the density of particles as a function of the altitude and the pressure as a function of the
number N of particles. The atmosphere is found to be exponential far enough from the piston, and the “granular temperature”, T, dependence on the piston velocity, V, is of the form , where is a decreasing function of N. This may explain previous conflicting numerical results.
Received 1 February 1999 相似文献
10.
The avalanche mixing of granular solids in a slowly rotated 2D upright drum is studied. We demonstrate that the account of
the difference δ between the angle of marginal stability and the angle of repose of the granular material leads to a restricted
value of the mixing time τ for a half filled drum. The process of mixing is described by a linear discrete difference equation.
We show that the mixing looks like linear diffusion of fractions with the diffusion coefficient vanishing when δ is an integer
part of π. Introduction of fluctuations of δ suppresses the singularities of τ(δ) and smoothes the dependence τ(δ).
Received 27 October 2000 and Received in final form 13 March 2001 相似文献
11.
We introduce the model of inelastic hard spheres with random restitution coefficient α, in order to account for the fact that,
in a vertically shaken granular system interacting elastically with the vibrating boundary, the energy injected vertically
is transferred to the horizontal degrees of freedom through collisions only, which leads to heating through collisions, i.e. to inelastic horizontal collisions with an effective restitution coefficient that can be larger than 1. This allows the system
to reach a non-equilibrium steady state, where we focus, in particular, on the single-particle velocity distribution f (v) in the horizontal plane, and on its deviation from a Maxwellian. Molecular Dynamics simulations and Direct Simulation Monte
Carlo (DSMC) show that, depending on the distribution of α, different shapes of f (v) can be obtained, with very different high-energy tails. Moreover, the fourth cumulant of the velocity distribution quantifying
the deviations from Gaussian statistics is obtained analytically from the Boltzmann equation and successfully tested against
the simulations.
Received 24 November 2000 and Received in final form 8 February 2001 相似文献
12.
M. Coraddu M. Lissia G. Mezzorani P. Quarati 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(1-2):11-15
In fusion reactions, the Coulomb barrier selects particles from
the high-momentum part of the distribution. Therefore, small
variations of the high-momentum tail of the velocity distribution
can produce strong effects on fusion rates. In plasmas several
potential mechanisms exist that can produce deviations from the
standard Maxwell-Boltzmann distribution. Quantum broadening of
the energy-momentum dispersion relation of the plasma
quasi-particles modifies the high-momentum tail and could explain
the fusion-rate enhancement observed in low-energy nuclear
reaction experiments. 相似文献
13.
Pica Ciamarra M Coniglio A Nicodemi M 《The European physical journal. E, Soft matter》2007,22(3):227-234
We overview the physics of a granular mixture subject to horizontal oscillations,
recently investigated via experiments and molecular dynamics simulations.
First we discuss the rich phenomenology exhibited by this system, which encompasses
both segregation and dynamical instabilities.
Then we show that the phenomenology can be explained
via an effective interaction approach, by which the driven,
non-thermal, granular mixture in mapped into a monodispersed thermal
system of particles interacting via an effective potential.
After determining the effective interaction we discuss its
microscopic origin and investigate how it induces the observed
phenomenology. Finally, as much as in thermal fluids, from the
effective interaction we derive a Cahn-Hilliard dynamics equation,
which appears to capture the essential characteristics of the dynamics
of the granular mixture. 相似文献
14.
The silo discharge process is studied by molecular
dynamics simulations. The development of the velocity profile and
the probability density function for the displacements in the
horizontal and vertical axis are obtained. The PDFs obtained at
the beginning of the discharge reveal non-Gaussian statistics and
superdiffusive behaviors. When the stationary flow is developed,
the PDFs at shorter temporal scales are non-Gaussian too. For big
orifices a well-defined transition between ballistic and diffusive
regime is observed. In the case of a small outlet orifice, no
well-defined transition is observed. We use a nonlinear diffusion
equation introduced in the framework of non-extensive
thermodynamics in order to describe the movements of the grains.
The solution of this equation gives a well-defined relationship
(γ= 2/(3-q)) between the anomalous diffusion exponent
γ and the entropic parameter q introduced by the
non-extensive formalism to fit the PDF of the fluctuations. 相似文献
15.
D. Mostacci V. Molinari M. Premuda 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(1):127-132
The percolation of a liquid through a porous material is investigated with the help of equations of the Onsager type. An expression
is derived for the
molecular attraction, starting from Sutherland’s potential approximation to
the van der Waals interaction. Then appropriate Onsager equations
incorporating this molecular attraction are written from transport theory
considerations, in terms of dimensionless variables. As an application, the
system of self-similar equations so derived is applied to a simplified
situation. 相似文献
16.
17.
Soulié F El Youssoufi MS Cherblanc F Saix C 《The European physical journal. E, Soft matter》2006,21(4):349-357
We investigate the macroscopic mechanical behaviour of wet polydisperse granular media. Capillary bonding between two grains
of unequal diameters is described by a realistic force law implemented in a molecular-dynamics algorithm together with a protocol
for the distribution of water in the bulk. Axial-compression tests are simulated for granular samples at different levels
of water content, and compared to experiments performed in similar conditions. We find good agreement between numerical and
experimental data in terms of the rupture strength as a function of water content. Our results show the importance of the
distribution of water for the mechanical behaviour. 相似文献
18.
Vibrated powders exhibit striking phenomena: subharmonic waves, oscillons, convection, heaping, and even bubbling. We demonstrate novel rectangular profile subharmonic waves for vibrated granular material, that occur uniquely in the two-phase case of grains, and a fluid, such as air. These waves differ substantially from those for the gas-free case, exhibit different dispersion relations, and occur for specific shaking parameters and air pressure, understandable with gas-particle flow models. These waves occur when the gas diffusively penetrates the granular layer in a time comparable to the shaker period. As the pressure is lowered towards P =0, the granular-gas system exhibits a Knudsen regime. This instability provides an opportunity to quantitatively test models of two-phase flow. 相似文献
19.
T. Neumann 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(1):133-138
Cellular automata models play an important role in traffic modeling. For some variants of the Nagel-Schreckenberg model, the
effects of traffic light boundary conditions are considered. Based on previous results, the exact density profiles can be
derived easily for deterministic dynamics. Additionally, the exact average outflow per traffic light cycle is presented not
only in the deterministic case, but also for an important semi-stochastic variant with slow-to-start behaviour. Thereby, the
models are strongly related to the well-known totally asymmetric simple exclusion process (TASEP) which can be regarded as
a generic model for many driven particle systems. 相似文献