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.
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
3.
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
4.
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
5.
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
6.
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
7.
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
8.
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
9.
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
10.
In horizontally shaken granular material different types of pattern formation have been reported. We want to deal with the
convection instability which has been observed in experiments and which recently has been investigated numerically. Using
two dimensional molecular dynamics we show that the convection pattern depends crucially on the inelastic properties of the
material. The concept of restitution coefficient provides arguments for the change of the behaviour with varying inelasticity.
Received 3 March 1999 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.
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
13.
A. Aradian E. Raphaël P.G. de Gennes 《The European physical journal. E, Soft matter》2000,2(4):367-376
We consider a porous solid covered with a water film (or with a drop) in situations where the liquid is pumped in, either
spontaneously (if the porous medium is hydrophilic) or mechanically (by an external pump). The dynamics of dewetting is then
strongly modified. We analyse a few major examples, a) horizontal films, which break at a certain critical thickness, b) the
“modified Landau-Levich problem” where a porous plate moves up from a bath and carries a film: aspiration towards the plate
limits the height H reached by the film, c) certain situation where the hysteresis of contact angles is important.
Received 5 October 1999 and Received in final form 7 February 2000 相似文献
14.
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
15.
T. Le Pennec M. Ammi J.C. Messager A. Valance 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(4):657-664
We report here experiments on two-dimensional funnel flow of diameter glass beads on an inclined plane. We have investigated the properties of the flow according to the outlet size D of the funnel and the gravity. We have identified three different regimes. For small funnel outlet sizes, there is no significant
change in flow density: the flow is rather steady and homogeneous. For intermediate outlet sizes (), the flow is intermittent, consisting of spatially ordered density waves propagating upwards. At bigger outlet sizes, density
waves do not exhibit any ordering and the flow dynamics becomes chaotic. In addition, we find that the flow dynamics is independent
of the funnel opening angle except close to the channel flow configuration. Finally, it is stressed that the interactions
between the beads and the inclined plane play a crucial role in the mechanism of formation of density waves.
Received: 9 July 1998 / Received in final form and Accepted: 18 September 1998 相似文献
16.
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
17.
E. Falcon C. Laroche S. Fauve C. Coste 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(1):45-57
An experimental study of the behavior of one bead bouncing repeatedly off a static flat horizontal surface is presented. We
observe that the number of bounces made by the bead is finite. When the duration between two successive bounces becomes of
the order of the impact duration, the bead no longer bounces but oscillates on the elastically deformed surface before coming
to rest. This transition is explained with a modified Hertz interaction law in which gravity is taken into account during
the interaction. For each bounce, measurement of both the duration of collision and the restitution coefficient have been
done. The effective restitution coefficient is essentially constant and close to 1 during almost all bounces before decreasing
to zero when the impact velocity vanishes. This is due to an interplay between gravity and viscoelastic dissipation.
Received: 2 December 1997 / Accepted: 5 March 1998 相似文献
18.
Grain segregation mechanism in aeolian sand ripples 总被引:2,自引:0,他引:2
H.A. Makse 《The European physical journal. E, Soft matter》2000,1(2-3):127-135
Many sedimentary rocks are formed by migration of sand ripples. Thin layers of coarse and fine sand are present in these rocks,
and understanding how layers in sandstone are created has been a longstanding question. Here, we propose a mechanism for the
origin of the most common layered sedimentary structures such as inverse graded climbing ripple lamination and cross-stratification
patterns. The mechanism involves a competition between three segregation processes: (i) size-segregation and (ii) shape-segregation
during transport and rolling, and (iii) size segregation due to different hopping lengths of the small and large grains. We
develop a discrete model of grain dynamics which incorporates the coupling between moving grains and the static sand surface,
as well as the different properties of grains, such as size and roughness, in order to test the plausibility of this physical
mechanism.
Received 19 July 1999 and Received in final form 4 August 1999 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.
Scaling approach of the convective drying of a porous medium 总被引:1,自引:0,他引:1
P. Coussot 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):557-566
We propose a simplified, theoretical approach of the evolution of liquid distribution during the convective drying of a granular
packing. In the absence of gravity effects three regimes are distinguished according to the relative importance of surface
evaporation, capillarity or evaporation from the interior of the sample. The evolution of the drying rate as a function of
the saturation can be inferred from the characteristic velocities associated to each of these effects. We also carried out
drying experiments of bead packings saturated with ethanol, at four different velocities of the boundary convection current,
and with bead size ranging from 4.5 to 100 μm. The drying curves exhibit different regimes with a scaling as a function of
particle radius and current velocity as predicted by the theory.
Received 7 June 1999 and Received in final form 25 October 1999 相似文献