arXiv subjects

P. Evesque

Publications and source records attributed to P. Evesque.

At least 19 recordsLinked to original sources

arXiv2011

Microgravity and Dissipative Granular Gas in a vibrated container: a gas with an asymmetric speed distribution in the vibration direction, but with a null mean speed everywhere

The main topic of this paper (part 4) is the interpretation of data from extended simulations published in previous Poudres & Grains (see P&G 17, #1 to #18) concerning the dynamics of N equal-size spheres in a 3d rectangular cell excited along Oz in 0 gravity.(N=100, 500, 1000, 1200, 2000, 3000, 4000, 4500). Different Oz excitation kinds have been used (symmetric and non symmetric bi-parabolic, symmetric and non symmetric saw teeth, thermal wall). No rotation is included, dissipation is introduced via a restitution coefficient e= -V'n/Vn, where V'n and Vn are the relative ball speed along normal to ball centres after and before collision. It is proved that the local speed distribution along z is fundamentally dissymmetric in most part of the cell while the mean local speed is 0. This demonstrates the inability of a model based on a thermal bath (with a single local temperature) to describe this dissipative-granular-gas-system, even when assuming that this temperature varies in space. The other (1-3) parts sum up few results obtained in the very low density regime.

physics.flu-dyn↗

arXiv2011

Boundary conditions and the dynamics of a dissipative granular gas: slightly dense case

The effect of different possible kinds of motion of the exciting walls (cyclic, random, ...) is investigated on the dynamics of a granular dissipative gas. It is shown that the real distribution of speed of the wall which interact with the balls depend strongly on the real ball speed, due to a screening effect, so that the transfer of excitation from the walls to the cloud of particles may drastically depend on the ball speed itself. This makes the excitation quite non linear, with a change of efficiency law. This may explain the observation of a biphasic cloud when the mean free path of balls is slightly smaller than the cell size L, or may predict that the particles in the cloud is merely at rest as soon as the mean free path is smaller than L/10. It is obvious that the vibrating cell cannot be considered as a thermostat.

physics.flu-dyn↗

arXiv2011

Granular Media under Vibration in Zero Gravity: Transition from Rattling to Granular Gas

We report on different experimental behaviours of granular dissipative matter excited by vibration as studied during the 43rd ESA campaign of Airbus A300-0g from CNES. The effect of g-jitter is quantified through the generation of a rattle effect. The French-European team's electromagnetic set-up is used, with 20Hz cam recording and high speed camera for a short duration (1s) during each parabola.

physics.flu-dyn↗

arXiv2011

On the complexity/criticality of Jamming during the discharge of granular matter from a silo

This paper is aimed at pursuing a recent discussion about the comparison between Self-Organised Criticality, the jamming process and the percolation theory in the problem of a silo discharge [I. Zuriguel, A. Garcimartin, D. Maza, L.A.Pugnaloni, J.M.Pastor, "Jamming during the discharge of granular matter from a silo", Phys.Rev.E 71, 051303 (2005)]. Statistics of blocking a silo is investigated from different models: percolation, self organised criticality..

physics.flu-dyn↗

arXiv2011

How one can make the bifurcation of Maxwell's demon in Granular Gas Hyper-Critical

Experimental data from Maxwell's demon experiments on granular gas are revisited. It is shown that the transition nature changes from critical to sub-critical via a tri-critical point when frequency of vibration is increased continuously. So (i) the transition is not hyper-critical as asserted previously, but (ii) the fluctuations amplitude is spontaneously reinforced at the tri-critical point compared to the one at other frequencies. So, (iii) this analysis still contradicts a recent study which asserts that the bifurcation is always critical, and that fluctuations shall depend on the number of grains only. Beside, (iv) it is proposed a way to build an experiment, based on some modification of the "Maxwell's demon in granular gas" set up, which undergoes a hyper-critical bifurcation, with the use of some controlled feed-back of the flows. This last idea can be generalised and used in other domains where bifurcation theory applies, i.e. physics, chemistry, population dynamics, economy, to improve regulation, but generating hyper- fluctuations. Finally it is shown that the dynamical result is sensitive to the very-details of the regulation.

physics.flu-dyn↗

arXiv2011

Cyclic Maxwell Demon in granular gas using 2 kinds of spheres with different masses

The problem of Maxwell's demon in granular gas is revisited in the case of a mixture of two particle species. The phase space is found to be 2d. Existence of cyclic orbits, with periodic segregation, is demonstrated by investigating the case of 2 kinds of particles with identical parameters but different masses. At large excitation equi-partition shall be obtained, but convergence towards the steady state is found in spiral. The spiral convergence is imposed due to the rule of kinetic-energy transfer between the two species. It results that the most probable scenario is that the steady state breaks into cyclic orbit at lower amplitude of vibration below a bifurcation threshold. The nature of the bifurcation is not known; it can be critical, subcritical, hypercritical or can exhibit a tri-critical point as varying the control parameters. No conclusion is obtained at very low vibration amplitude: it is guessed two scenarii under further cooling which generates Maxwell's demon and segregation..

physics.flu-dyn↗

arXiv2006

Maxwell demon in Granular gas: a new kind of bifurcation? The hypercritical bifurcation

This paper starts with the investigation of the behaviour of a set of two subsystems which are able to exchange some internal quantity according to a given flux function. It is found that this sytem exhibit a bifurcation when the flux passes through a maximum and that its kind (super-critical/sub-critical) depends on the dissymmetry of the flux function near the maximum. It is also found a new kind of bifurcation when the flux function is symmetric: we call it hypercritical bifurcation because it generates much stronger fluctuations than the super-critical one. The effect of a white noise is then investigated. We show that an experimental set-up, leading to the Maxwell demon in granular gas, displays all these kinds of bifurcation, just by changing the parameters of excitation. It means that this system is much less simple as it was thought.

physics.flu-dyn↗

arXiv2006

Collision statistics in a dilute granular gas fluidized by vibrations in low gravity

We report an experimental study of a dilute "gas" of inelastically colliding particles excited by vibrations in low gravity. We show that recording the collision frequency together with the impulses on a wall of the container gives access to several quantities of interest. We observe that the mean collision frequency does not scale linearly with the number N of particles in the container. This is due to the dissipative nature of the collisions and is also directly related to the non extensive behaviour of the kinetic energy (the granular temperature is not intensive).

cond-mat.other↗

arXiv2005

Is the friction angle the maximum slope of a free surface of a non cohesive material?

Starting from a symmetric triangular pile with a horizontal basis and rotating the basis in the vertical plane, we have determined the evolution of the stress distribution as a function of the basis inclination using Finite Elements method with an elastic-perfectly plastic constitutive model, defined by its friction angle, without cohesion. It is found that when the yield function is the Drucker-Prager one, stress distribution satisfying equilibrium can be found even when one of the free-surface slopes is larger than the friction angle. This means that piles with a slope larger than the friction angle can be (at least) marginally stable and that slope rotation is not always a destabilising perturbation direction. On the contrary, it is found that the slope cannot overpass the friction angle when a Mohr-Coulomb yield function is used. Theoretical explanation of these facts is given which enlightens the role plaid by the intermediate principal stress in both cases of the Mohr-Coulomb criterion and of the Drucker-Prager one. It is then argued that the Mohr-Coulomb criterion assumes a spontaneous symmetry breaking, as soon as the two smallest principal stresses are different ; this is not physical most likely; so this criterion shall be replaced by a Drucker-Prager criterion in the vicinity of the equality, which leads to the previous anomalous behaviour ; so these numerical computations enlighten the avalanche process: they show that no dynamical angle larger than the static one is needed to understand avalanching. It is in agreement with previous experimental results. Furthermore, these results show that the maximum angle of repose can be modified using cyclic rotations; we propose a procedure that allows to achieve a maximum angle of repose to be equal to the friction angle .

cond-mat.soft↗

arXiv2005

Quasi-static mechanics of granular materials

This textbook in French describes the rheology of granular materials in the quasi static regime at a macroscopic scale. It starts defining cohesion, friction and the Coulomb approach, from the large-strain range. Then it focuses on the range of small and intermediate deformation when the medium can dilate if it is dense; different specific typical tests (oedometric, constant pressure, constant volume) are defined, the behaviours they lead are carefully described and their dependences upon initial density recalled. Roles of friction and dilatancy are exemplified and their link with the deviatoric stress too. "Natural" "phase space" is defined, which is (specific volume, mean pressure, axial or deviatoric stress). Then the "critical" state, the "characteristic" state and the Rowe's law of dilatancy are defined, and the previous behaviours analysed in term of plastic deformation, showing that these behaviours obey a specific rule of dissipation. An isotropic incremental modelling is then proposed and studied, with a pseudo Poisson coefficient that evolves with the stress ratio. It shows a good agreement with experimental trends, while the theory keeps simple, which describes in particular the isochoric compression and the oedometric compression correctly. Cyclic behaviours are then described, and their link with soil liquefaction, with a peculiar attention to the role of stress ratio. Basic concepts on micro-macro passage are given, starting with a theoretical approach leading to an exponential distribution of forces ; then it proposes a theory for the compaction of the medium with pressure, that predicts the v-log(p) law for the critical state.

cond-mat.soft↗

arXiv2005

On few aspects of the dynamics of granular matter

This paper, in French, describes a series of completely different behaviours of the mechanics of granular matter, which are obtained experimentally using periodic forcing at different amplitude, frequency and orientation. It starts with the problem of granular dissipative gas which has been investigated in micro-gravity ; it is found that such a gas exists only at very low density ; it is shown also that clustering occurs at larger density. Is this a phase transition ? The problem of dissipative Sinai billiard is then investigated briefly ; is it ergodic ? An experiment on propagation of acoustic wave is studied, with peculiar attention paid to scattering and diffusion that occurs when acoustic wavelength is comparable to the grain size. A third experiment demonstrates that bulk convection can be induced by slow (quasi static) horizontal forcing ; this flow is related to the quasi static rheology of granular matter, but looks rather like convection occurring under "dynamic vibration". A fourth experiment describes pure inertial effect, making the sand behaving as a perfect (non viscous) fluid ; in particular, it is shown that a static swell 9that does not propagate) is enforced at the interface between liquid and sand by strong periodic horizontal forcing . Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn

cond-mat.soft↗

arXiv2005

New corner stones in dissipative granular gases

Theory of granular dissipative gas is discussed based on Boltzmann's equation and in view of recent experimental results in micro-gravity during few CNES and ESA campaigns [9,11]. It is recalled that the Boltzmann's distribution is a steady solution only when collisions are elastic; hence it is not applicable in the case of dissipative granular gas. The first experimental case concerns non-interacting balls in a vibrated cylindrical box, which proves that rotation-induced dissipation has important consequence: it reduces the efficient phase space dimension of this billiard-like system from 13-d to 1-d, since the motion is 1d and quasi-periodic for large enough forcing; the result remains valid with 2 balls. The second experiment concern the dynamics of interacting particles in the case of a small number (N= 12,24,36,48) of grains: The typical speed of a balls is found to vary linearly with the piston speed, but decreases when the number of balls N increases. The distribution of waiting times T1 between successive ball-gauge collisions follows an exponential distribution experimentally, i.e. P(T1)= exp(-T1/To), proving uncorrelated motions of balls. The amplitude I of the ball-gauge impacts is found to decrease exponentially p(I)=exp(-I/Io).This is temptatively explained using a model "a la Boltzmann" associated with the notion of "velostat", and a second model is proposed based on dissipation. Experiments show the coupling between rotation and translation during collisions cannot be neglected, because it generates efficient dissipation.

cond-mat.soft↗

arXiv2005

p=constant compression on loose Hostun sand: The case of an anisotropic response

Experimental data from axially symmetric compression test at constant mean pressure p on Hostun sand from Flavigny experiments on loose sands are used to study the validity of an "isotropic" modelling at different densities . It is found that the material response is not isotropic even at small deviatoric stress. As an "isotropic" behaviour is found for compression test at constant volume on the same sand, this new result questions the unicity of the trajectory in the classical phase space of soil mechanics (q,p,v), with q being thed deviatoric stress, v the specific volume. This asks whether the space shall be taken larger than 3d or not. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn

cond-mat.soft↗

arXiv2005

Limits of isotropic plastic deformation of Bangkok clay

A model assuming incremental plastic isotropic response has been recently proposed to model the deformation of isotropic packing of grains, in the small-strain range. It is used here on over-consolidated remould clay, to interpret the small-strain range behaviour obtained in [1,2] on Bangkok clay. The data published in [1,2] at constant volume are also used here to measure the size of the domain of validity in the (q/(M'p), p/po) plane, where po is the over-consolidation isotropic pressure, p is the mean stress and q the deviatoric stress, q . So, it is shown that the model works also for clay. This enlarges the application domain of model [3,4] to soft clay with OCR larger than 1.2 to 1.5. Pacs # : 45.70.-n ; 62.20.Fe ; 83.80.Fg, 83.80.Hj

cond-mat.soft↗

arXiv2005

Experimental Test of the validity of "Isotropic" Approximation for the Mechanical Behaviour of Clay

Experimental data from axially symmetric compression test at constant mean pressure p on kaolinite clay are used to study the validity of an "isotropic" modelling as a function of the overconsolidation ratio (OCR).The isotropic assumption is found to be quite good for 2 4. For very large OCR (OCR >10), anisotropic response is observed at few percents of axial deformation. Relation with anisotropic distribution of local forces is made. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn

cond-mat.soft↗

arXiv2005

Experimental Test of the "Isotropic" Approximation for Granular Materials using p=constant Compression

Experimental data from axially symmetric compression test at constant mean pressure p on Hostun sand from Bouvard experiments are used to study the validity of an "isotropic" modelling as a function of the density .The isotropic assumption is found to be quite good for loose samples and/or in the range of large pressure. For smaller mean pressure, anisotropic response is observed at few percents of axial deformation. Relation with anisotropic distribution of local force is made. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn

cond-mat.soft↗

arXiv2005

Trajectories of loose sand samples in the Phase Space of Soil Mechanics

In general, the evolution of soil submitted to simple stress-strain paths is characterised using the 3d phase space (v,p',q) i.e. (specific volume, mean intergranular pressure, deviatoric stress q. When uniaxial compressions is performed at constant lateral pressure p' or at constant mean pressure p', one finds that all trajectories end up at a line of attracting point called the critical-state line via the surface of Roscoe or of Hvorslev depending if the initial volume is the loosest possible one (at a given p') or densest. Trajectories of weakly dense samples are not often reported in this phase space. We find here that they shall present some sigmoid shape as it can be found from soil mechanics argument. This seems to indicate that Roscoe's surface shall exhibit a singularity at the critical point.

cond-mat.soft↗

arXiv2005

Experimental Proof of the Existence of a Bifurcation Process During the undrained test in Clay

Recent papers, based on a new simple incremental modelling which assumes an "isotropic" response, predicts that the trajectory followed during an undrained compression test exhibits a bifurcation process when the stress field arrives at q=M'p', where q stands for the deviatoric stress, p' for the mean stress and M' is a coefficient describing friction. This indicates a discontinuous change of solution when arriving at q=M'p'. This paper looks at experimental data on dense sample obtained at p'=constant, and it shows that the trajectory (p'=constant, v=constant) does continue to exist at and beyond the q=M'p' plane. So, this demonstrates the validity of the analysis which uses the bifurcation theory and this strengthens the proposed modelling. Indeed, this demonstrates the reality of the bifurcation process during undrained compression. Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn

cond-mat.soft↗