共查询到20条相似文献,搜索用时 15 毫秒
1.
P. Boltenhagen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):75-78
We have studied the maximal angle of stability of a granular packing confined between two walls. The effect of the walls is
to increase the angle dramatically. The decay of the angle with the distance between the walls is exponential with a characteristic
length which is a function of the beads diameter. The effect of the roughness of the walls has been also studied.
Received 1 April 1999 相似文献
2.
V. Buchholtz J.A. Freund T. Pöschel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):169-182
We investigate autogenous fragmentation of dry granular material in rotating cylinders using two-dimensional molecular dynamics.
By evaluation of spatial force distributions achieved numerically for various rotation velocities we argue that comminution
occurs mainly due to the existence of force chains. A statistical analysis of these force chains explains the spatial distribution
of comminution efficiency in ball mills as measured experimentally by Rothkegel [1] and Rolf [2]. For animated sequences of
our simulations see http://summa.physik.hu-berlin.de/kies/mill/bm.html
Received 19 January 2000 相似文献
3.
S. Renard T. Schwager T. Pöschel C. Salueña 《The European physical journal. E, Soft matter》2001,4(2):233-239
The onset of surface fluidization of granular material in a vertically vibrated container, z = A cosωt
, is studied experimentally. Recently, for a column of spheres it has been theoretically found (see T. P?schel, T. Schwager,
C. Salue na, Phys. Rev. E 62, 1361 (2000)) that the particles lose contact if a certain condition for the acceleration amplitude ≡Aω2/g = f (ω) holds. This result is in disagreement with other findings where the criterion = = const was found to be the criterion of fluidization. We show that for a column of spheres a critical acceleration is not
a proper criterion for fluidization and compare the results with theory.
Received 21 August 2000 and Received in final form 30 October 2000 相似文献
4.
A model for ripple instabilities in granular media 总被引:1,自引:0,他引:1
O. Terzidis P. Claudin J.-P. Bouchaud 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):245-249
We extend the model of surface granular flow proposed in [#!bcre!#] to account for the effect of an external `wind', which
acts as to dislodge particles from the static bed, such that a stationary state of flowing grains is reached. We discuss in
detail how this mechanism can be described in a phenomenological way, and show that a flat bed is linearly unstable against
ripple formation in a certain region of parameter space. We focus in particular on the (realistic) case where the migration
velocity of the instability is much smaller than the grains' velocity. In this limit, the full dispersion relation can be
established. We relate the critical wave vector to the mean hopping length and to the ratio of the flight time to the `stick'
time. We provide an intuitive interpretation of the instability.
Received: 30 January 1998 / Revised: 12 May 1998 / Accepted: 8 June 1998 相似文献
5.
N.V. Brilliantov T. Pöschel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):299-301
We show that two basic mechanical processes, the collision of particles and rolling motion of a sphere on a plane, are intimately
related. According to our recent findings, the restitution coefficient for colliding spherical particles , which characterizes the energy loss upon collision, is directly related to the rolling friction coefficient for a viscous sphere on a hard plane. We quantify both coefficients in terms of material constants which allows to determine
either of them provided the other is known. This relation between the coefficients may give rise to a novel experimental technique
to determine alternatively the coefficient of restitution or the coefficient of rolling friction.
Received 5 May 1999 相似文献
6.
N. Fraysse H. Thomé L. Petit 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):615-619
Humidity is well-known to significantly affect the mechanical properties, static as well as dynamic, of granular materials.
We present the method of humidification of granular media from an under-saturated vapor that we designed in order to experimentally
quantify such moisture-induced effects under accurately-controlled humidity conditions. We report the quantitative measurements
of the maximum angle of stability of a pile made of small glass beads, as a function of the relative vapor pressure, up to
close to saturation. The results obtained with liquids differing in their wetting properties on glass, namely water and heptane,
are presented. It is shown that the wetting properties of the liquid on the grains have a strong influence on the cohesion
of the non-saturated granular medium.
Received 26 October 1998 and Received in final form 30 March 1999 相似文献
7.
Dynamics of aeolian sand ripples 总被引:1,自引:0,他引:1
Z. Csahók C. Misbah F. Rioual A. Valance 《The European physical journal. E, Soft matter》2000,3(1):71-86
We analyze theoretically the dynamics of aeolian sand ripples. In order to put the study in the context, we first review existing
models. This paper is a continuation of two previous papers (Z. Csahók et al., Physica D 128, 87 (1999); A. Valance et al., Eur. Phys. J. B 10, 543 (1999)), the first one is based on symmetries and the second on a hydrodynamical model. We show how the hydrodynamical
model may be modified to recover the missing terms that are dictated by symmetries. The symmetry and conservation arguments
are powerful in that the form of the equation is model-independent. We then present an extensive numerical and analytical
analysis of the generic sand ripple equation. We find that at the initial stage the wavelength of the ripple is that corresponding
to the linearly most dangerous mode. At later stages the profile undergoes a coarsening process leading to a significant increase
of the wavelength. We find that including the next higher-order nonlinear term in the equation leads naturally to a saturation
of the local slope. We analyze both analytically and numerically the coarsening stage, in terms of a dynamical exponent for
the mean wavelength increase. We discuss some future lines of investigations.
Received 20 January 2000 相似文献
8.
A. Valance F. Rioual 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(3):543-548
Starting from the phenomenological model for sand ripple formation developed in [#!Bouchaud98!#], we proposed a new interpretation
in the light of recent experiments. Furthermore, we derive, close to the threshold of ripple instability, a nonlinear equation
for the spatio-temporal evolution of the sand bed profile, which to leading order has a quadratic nonlinearity. This equation
is identical to that derived recently on the basis of geometry and conservation law [#!Csahok98!#]. Our derivation connects
the coefficients of the nonlinear equation to the underlying physical mechanisms (reptation length...). This equation reveals
ripple structures which then undergo a coarsening process, as observed in wind tunnel experiment. Small, fast moving ripples
are absorbed by larger, slower forms resulting in a growth of the mean wavelength.
Received 5 January 1999 相似文献
9.
Y. Grasselli H.J. Herrmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):673-679
Experimental investigations on the shape of a heap formed in a Hele Shaw cell either on a flat base or in a two-dimensional
silo are presented. We have focused our attention on the shape dependence on mass flux and initial energy of particles poured
into the cell. Two kinds of granular media are considered: glass beads and sand and we shall point out their different behaviors.
We described the variations of the angle of repose and of the size of the tail as a function of the experimental parameters.
We also report the time evolution of the angle of repose during the formation of the heap.
Received 28 September 1998 and Received in final form 20 January 1999 相似文献
10.
J.M. Huntley 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):389-397
The force perturbation field in a two-dimensional pile of frictionless gravity-loaded discs or spheres arising from lattice
distortions is derived to first order. The starting point is the model proposed by Liffman et al. (Powder Technology (1992) pp. 255-267) and Hong (Phys. Rev. E 47, 760-762 (1993)) in which discs of uniform size are arranged on a regular lattice: this predicts a uniform normal stress
distribution at the base of the pile. The analysis is applied to two problems: (i) deformable (rather than rigid) grains that
undergo Hertzian deformation at the points of contact; (ii) a pile containing a gradient in particle size from the centre
to the free surfaces. The former results in the classical pressure dip at the centre; the latter also produces a dip if the
larger particles are at the centre.
Received 29 January 1998 and Received in final form 7 September 1998 相似文献
11.
L. Vanel E. Clément 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):525-533
We report sets of precise and reproducible measurements on the static pressure at the bottom of a granular column. We make
a quantitative analysis of the pressure saturation when the column height is increased. We evidence a great sensitivity of
the measurements with the global packing fraction and the eventual presence of shear bands at the boundaries. We also show
the limit of the classical Janssen model and discuss these experimental results under the scope of recently proposed theoretical
frameworks.
Received 7 September 1998 and Received in final form 28 January 1999 相似文献
12.
Saikat Chakraborty Prabhu R. Nott J. Ravi Prakash 《The European physical journal. E, Soft matter》2000,1(4):265-273
This paper considers the segregation of a granular mixture in a rotating drum. Extending a recent kinematic model for grain
transport on sandpile surfaces to the case of rotating drums, an analysis is presented for radial segregation in the rolling
regime, where a thin layer is avalanching down while the rest of the material follows rigid body rotation. We argue that segregation
is driven not just by differences in the angle of repose of the species, as has been assumed in earlier investigations, but
also by differences in the size and surface properties of the grains. The cases of grains differing only in size (slightly
or widely) and only in surface properties are considered, and the predictions are in qualitative agreement with observations.
The model yields results inconsistent with the assumptions for more general cases, and we speculate on how this may be corrected.
Received 4 June 1999 and Received in final form 28 September 1999 相似文献
13.
C. Coste B. Gilles 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(1):155-168
We discuss the acoustical behavior of a 1D model of granular medium, which is a chain of identical spherical beads. In this
geometry, we are able to test quantitatively alternative models to the Hertz theory of contact between elastic solids. We
compare the predictions of the different models to experimental results that concern linear sound wave propagation in the
chain submitted to a static force, and nonlinear solitary wave propagation in an unconstrained chain. We use elastic, elastic-plastic
and brittle materials, the beads roughness extends on one order of magnitude, and we also use oxidized metallic beads. We
demonstrate experimentally that at low static forces, for all types of beads, the linear acoustic waves propagate in the system
as predicted by Hertz's theory. At larger forces, after onset of permanent plastic deformation at the contacts, the brass
beads exhibit non Hertzian behavior, and hysteresis. Except in the case of brass beads, the nonlinear waves follow the predictions
of Hertz theory.
Revised: 28 May 1998 / Accepted: 27 July 1998 相似文献
14.
H.A. Makse 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(2):271-276
We study the segregation of granular mixtures in two-dimensional silos using a recently proposed set of coupled equations
for surface flows of grains. We study the thick flow regime, where the grains are segregated in the rolling phase. We incorporate
this dynamical segregation process, called kinematic sieving, free-surface segregation or percolation, into the theoretical
formalism and calculate the profiles of the rolling species and the concentration of grains in the bulk in the steady state.
Our solution shows the segregation of the mixture with the large grains being found at the bottom of the pile in qualitative
agreement with experiments.
Received: 6 July 1998 / Revised and Accepted: 13 August 1998 相似文献
15.
T. Boutreux H.A. Makse P.-G. de Gennes 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):105-115
We present the generalization of the minimal model for surface flows of granular mixtures, proposed by Boutreux and de Gennes
[J. Phys. I France 6, 1295 (1996)]. The minimal model was valid for grains differing only in their surface properties. The present model also
takes into account differences in the size of the grains. We apply the model to study segregation in two-dimensional silos
of mixtures of grains differing in size and/or surface properties. When the difference in size is small, the model predicts
that a continuous segregation appears in the static phase during the filling of a silo. When the difference in size is wide,
we take into account the segregation of the grains in the rolling phase, and the model predicts complete segregation and stratification
in agreement with experimental observations.
Received 9 September 1998 and Received in final form 4 November 1998 相似文献
16.
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
17.
T. Boutreux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):419-424
We present the generalization of a theoretical model for segregation of granular mixtures due to surface flows, published
in J. Phys. I France 6, 1295 (1996). Our generalized model is valid for grains differing by their size and/or their surface properties; in the present
paper, we describe the case of two species with the same surface properties but two different sizes. The rolling stream is
assumed to be homogeneous. Exchanges between the grains at rest and the rolling stream are modelized via binary collisions.
The model predicts that during the filling of a two-dimensional silo, continuous segregation appears inside the static phase: small (respectively large) grains tend to stop uphill (respectively downhill), although
both species remain present everywhere. This fits the observations when the size difference between the species is small.
When the size difference is large, a different regime is observed. We argue that in this case, segregation occurs directly inside the rolling stream.
Received: 25 February 1998 / Received in final form and Accepted: 6 July 1998 相似文献
18.
The compaction of granular packings or soils is a collective process which for higher densities becomes increasingly slower
reaching glassy behaviour. We present a study of this problem from various points of view, in particular we will represent
the evolving force network that percolates through the system by an inverse fiber rupture model.
Received 15 March 2002 and Received in final form 29 July 2002 相似文献
19.
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
20.
Oger L Ammi M Valance A Beladjine D 《The European physical journal. E, Soft matter》2005,17(4):467-476
We performed numerical simulations of one-bead collision on the surface of a static granular medium. The simulations have been done for two- and three-dimensional packings of beads. The effect of the incident bead velocity, the shot angle, the mechanical parameters and the packing structure are analyzed for ordered and disordered 2D packings and only disordered 3D packings. The 2D results are in good agreement with experimental available data. The 3D simulations give good preliminaries results about the shock-wave propagation through the stacking and provides new insights in the ejection process (“splash function”). 相似文献