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1.
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
2.
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
3.
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
4.
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
5.
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
6.
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
7.
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
8.
In a previous work [#!ref1!#], the flow velocity of a steady two-dimensional granular flow along an inclined wall was investigated.
The scaling law for the velocity field was found in good agreement with recent experimental results. The purpose of the present
paper is to reformulate in more systematic manner and in a somewhat more general context the equations of mass and momentum
conservation for dense granular flow, and also to present some new results with particular emphasis on roughness influence
and dynamic dilatancy. Theoretical results are found in good agreement with experiments.
Received 19 July 1999 and Received in final form 14 October 1999 相似文献
9.
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
10.
We present extensive computational results for the effective temperature,
defined by the fluctuation-dissipation relation between the mean square
displacement and the average displacement of grains, under the action of
a weak, external perturbation, of a sheared, bi-disperse granular packing
of compressible spheres. We study the dependence of this parameter on the
shear rate and volume fractions, the type of particle and the observable
in the fluctuation-dissipation relation. We find the same temperature
for different tracer particles in the system. The temperature becomes
independent on the shear rate for slow enough shear suggesting that it is
the effective temperature of the jammed packing. However, we also show
that the agreement of the effective temperature for different observables
is only approximate, for very long times, suggesting that this defintion
may not capture the full thermodynamics of the system. On the other hand,
we find good agreement between the dynamical effective temperature and a
compactivity calculated assuming that all jammed states are equiprobable.
Therefore, this definition of temperature may capture an instance
of the ergodic hypothesis for granular materials as proposed by theoretical
formalisms for jamming. Finally, our simulations indicate
that the average shear
stress and apparent shear viscosity follow the usual relation with the shear
rate for complex fluids. Our results show that the application of
shear induces jamming in packings whose particles interact
by tangential forces. 相似文献
11.
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
12.
E. Kolb T. Mazozi E. Clément J. Duran 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):483-491
We present series of experiments on the resistance force encountered by a bottom piston pushing a vertical granular column
confined in a two-dimensional cell. We show that, due to the presence of friction at the boundaries and between the grains,
the signal shows many complex features. At slow driving velocities, we observe a transition to a stick-slip dynamic instability.
Depending on the granular material used, the elementary stick-slip events may either be well characterized or largely distributed.
We present a statistical study on the waiting time between events and the distribution of energy release as a function of
the spring stiffness and the driving velocity.
Received 5 August 1998 and Received in final form 22 October 1998 相似文献
13.
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
14.
A. Valance T. Le Pennec 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):223-229
We study granular flows through narrow channels driven by gravity in the framework of the kinetic theory for dissipative dense
gases. We derive equations of motion for quasi-one-dimensional systems. In a certain range of flow density, the steady homogeneous
regime is found to be unstable against the formation of density waves. We show moreover that near the onset of the instability,
the governing equation for the flow density is a mixture of the Korteweg-de-Vries equation, which leads to soliton, and the
Bürger equation which exhibits spatio-temporal chaos. The competition between chaos and solitons may lead either to regular
spatially ordered density waves or to chaotic dynamics. We argue that these two types of dynamics can be encountered experimentally
according to the channel width and the dissipative properties of the granular media.
Received: 11 March 1998 / Revised and Accepted: 3 July 1998 相似文献
15.
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
16.
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
17.
V. Garzó 《The European physical journal. E, Soft matter》2009,29(3):261-274
A theory based on a solution of the inelastic Enskog equation that goes beyond the weak dissipation limit is used to determine
the thermal diffusion factor of a binary granular mixture under gravity. The Enskog equation that aims to describe moderate
densities neglects velocity correlations but retains spatial correlations arising from volume exclusion effects. As expected,
the thermal diffusion factor provides a segregation criterion that shows the transition between the Brazil-nut effect (BNE)
and the reverse Brazil-nut effect (RBNE) by varying the parameters of the system (masses, sizes, composition, density and
coefficients of restitution). The form of the phase diagrams for the BNE/RBNE transition is illustrated in detail in the tracer
limit case, showing that the phase diagrams depend sensitively on the value of gravity relative to the thermal gradient. Two
specific situations are considered: i) absence of gravity, and ii) homogeneous temperature. In the latter case, after some
approximations, our results are consistent with previous theoretical results derived from the Enskog equation. Our results
also indicate that the influence of dissipation on thermal diffusion is more important in the absence of gravity than in the
opposite limit. The present analysis, which is based on a preliminary short report of the author (Phys. Rev. E 78, 020301(R) (2008)), extends previous theoretical results derived in the dilute limit case. 相似文献
18.
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
19.
Fragmentation of grains in a two-dimensional packing 总被引:1,自引:0,他引:1
J.A. Åström H.J. Herrmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):551-554
A numerical model of fragmentation of a two-dimensional granular medium under pressure is investigated. The fragmentation
process is found to be strongly dependent on the type of force used as the criterion for breaking the grains. The fragmentation
mode affects the process less dramatically. There is a power-law divergence in the pressure when the medium approaches the
full packing limit, . Both log-normal and power-law fragment-size distributions are found. Gravity is demonstrated to be an important factor.
Received: 14 December 1997 / Accepted: 17 March 1998 相似文献
20.
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