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1.
The motion of a vibroimpacting one-degree-of-freedom model is analyzed. This model is motivated by the behavior of a shearing granular material, in which a transitional phenomenon is observed as the concentration of the grains decreases. This transition changes the motion of a granular assembly from an orderly shearing between two blocks sandwiching a single layer of grains to a chaotic shear flow of the whole granular mass. The model consists of a mass-spring-dashpot assembly that bounces between two rigid walls. The walls are prescribed to move harmonically in opposite phases. For low wall frequencies or small amplitudes, the motion of the mass is damped out, and it approaches a stationary state with zero velocity and displacement. In this paper, the stability of such a state and the transition into chaos are analyzed. It is shown that the state is always changed into a saddle point after a bifurcation. For some parameter combinations, horseshoe-like structures can be observed in the Poincare sections. Analyzing the stable and unstable manifolds of the saddle point, transversal homoclinic points are found to exist for some of these parameter combinations. (c) 1994 American Institute of Physics. 相似文献
2.
置于以窗口连接的分隔仓中振动驱动的颗粒气体会出现颗粒在两仓中布居分聚现象,被形象地称为麦克斯韦妖现象.通量模型的建立是理解麦克斯韦妖现象的关键问题.Eggers以颗粒气体动力学为基础得出了简化的理论模型.该模型可以很好地得到分仓中颗粒的布居分聚现象,然而似乎无法用于预测两种颗粒在分仓体系中的布居振荡现象.通过实验研究,测量了颗粒气体的流通量曲线,改进了Eggers模型.改进的模型可以很好地得到两种颗粒在分仓体系中的布居振荡现象.
关键词:
颗粒气体
耗散
通量模型 相似文献
3.
A bi-disperse granular gas in an asymmetrical two-compartment system is studied experimentally. The presence of asymmetry within the range of our experimental parameters results in a directed segregated state and a directed clustering state. This deterministic system does not depend on the initial conditions. A modified flux model based on Lohse's flux model for bi-disperse granular gases is derived. The modified flux model explains qualitatively the experimental results. 相似文献
4.
5.
We report experiments on the equipartition of kinetic energy in a mixture of pairs of different types of grains vibrated in two dimensions. In general, the two types of grains do not attain the same granular temperature, T(g) = 1/2m. However, the temperature ratio is constant in the bulk of the system and independent of the vibration velocity. The ratio depends strongly on the ratio of mass densities of the grains, but not on their inelasticity. Also, the temperature ratio is insensitive to compositional variables such as the number fraction of each component and the total number density. We conclude that a single granular temperature, as traditionally defined, does not characterize a multicomponent mixture. 相似文献
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7.
I. A. Kurzina E. V. Kozlov N. A. Popova M. P. Kalashnikov E. L. Nikonenko K. P. Savkin E. M. Oks Yu. P. Sharkeev 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(11):1238-1245
The results from quantitative investigations into the structural phase state of finely dispersed titanium before and after implantation with aluminum ions are presented. Two types of ??-Ti grains differing by phase composition, defect structure, and size are distinguished in the structure: fine grains in the range of 0.1?C0.5 ??m and coarse grains in the range of 0.5?C5 ??m. The presence of two types of TiO2 particles in the material, i.e., rounded particles found at dislocations in the bulk of the ??-Ti grains and lamellar particles found only inside coarse ??-Ti grains, is established. The formation of the Ti3Al phase is observed in the form of lamellar inclusions along the grain boundaries and rounded particles in triple joints. It is found that the particles of the TiAl3 phase are isolated with a smaller volume fraction than the Ti3Al phase; they are localized along the boundaries of coarse grains of the titanium matrix. It is established that the granular state and defect structure of the material change substantially after ion irradiation; i.e., the dislocation density and the fields of internal stresses in fine grains grow considerably, relative to the initial state of titanium. 相似文献
8.
The free cooling behavior of a wet granular gas is studied in one dimension. We employ a particularly simple model system in which the interaction of wet grains is characterized by a fixed energy loss assigned to each collision. Macroscopic laws of energy dissipation and cluster formation are studied on the basis of numerical simulations and mean-field analytical calculations. We find a number of remarkable scaling properties which may shed light on earlier unexplained results for related systems. 相似文献
9.
C. Laroche F. Pétrélis 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(4):489-492
We consider an ensemble of grains that interact through a dipole-dipole interaction. A granular gas is formed by the vertical
motion of a piston at the bottom boundary of the system. The interaction between the grains is controlled by an horizontally
applied magnetic field. When the speed of the piston is decreased, we observe a transition from a low density to a high density
phase. When the interaction between grains is weak, the transition is continuous. It is discontinuous for stronger interaction.
The phase diagram displays strong similarities with the ones observed for usual equilibrium phase transitions. 相似文献
10.
R. De Luca 《Physica C: Superconductivity and its Applications》2004,400(3-4):153-159
A bare three-dimensional model, in which grains are reduced to points, cannot fully account for the magnetic properties of granular superconductors. A dressed version of these network models is proposed to discuss the quantitative link between the low-field magnetic response of high-Tc superconducting granular samples and the characteristic properties of Josephson junction network models. By means of dressed models, the temperature dependence of the d.c. field-cooled susceptibility of a simple three-dimensional granular system, consisting of eight grains in a cubic arrangement, is studied. 相似文献
11.
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
12.
A. Garcimartín J. M. Pastor R. Arévalo D. Maza 《The European physical journal. Special topics》2007,146(1):331-340
When a granular layer is submitted to an oscillating
acceleration with a peak value larger than gravity, a large scale
motion develops. This movement is in some ways similar to the one
displayed by a liquid heated from below, and it is called granular
convection. Different conditions beside the parameters of the
forcing can affect it, such as the presence of an interstitial gas
or the roughness of the walls. We have carried out an experiment to
study the convective movement of a granular layer with a temporal
resolution high enough to describe the motion of individual grains
within one oscillating period. We also present experimental results
concerning the friction that the lateral walls exert on the grains
and its relevance on granular convection. 相似文献
13.
Assemblies of granular particles mechanically stable under their own weight contain arches. These are structural units identified as sets of mutually stable grains. It is generally assumed that these arches shield the weight above them and should bear most of the stress in the system. We test such hypothesis by studying the stress born by in-arch and out-of-arch grains. We show that, indeed, particles in arches withstand larger stresses. In particular, the isotropic stress tends to be larger for in-arch grains whereas the anisotropic component is marginally distinguishable between the two types of particles. The contact force distributions demonstrate that an exponential tail (compatible with the maximization of entropy under no extra constraints) is followed only by the out-of-arch contacts. In-arch contacts seem to be compatible with a Gaussian distribution consistent with a recently introduced approach that takes into account constraints imposed by the local force balance on grains. 相似文献
14.
T. F. Watson D. Belić P. Y. Convers E. J. Boyd S. A. Brown 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):81-85
Thin films produced by depositing tin clusters with sizes between 5 and 10 nm onto silicon nitride substrates were found to
be
highly coalesced resulting in grains with sizes ~30 nm. Exposing the clusters to nitrogen before they were deposited significantly
reduced the coalescence between them and resulted in granular films where the clusters mostly retained their shape. This is
due to a small
amount of tin nitride forming in the clusters. The coalesced and granular films were used to fabricate tin oxide gas sensors.
This was
done by depositing the two types of films onto silicon nitride chips and then oxidising them by baking at 250 °C for 24 h.
It was found that the sensors composed of uncoalesced clusters were much more sensitive to hydrogen. This was attributed to
the smaller grain size and the larger surface area of the granular films. 相似文献
15.
The understanding of the mechanisms leading to the formation of inhomogeneities in freely evolving granular gases is important
to establish, for instance, the time scale for pattern formation. In this work, the shear state of an isolated granular gas
will be analyzed. This is a two-band shear state with a steady density profile and an average temperature that decays in time
with a Haff like law, but controlled by the viscosity of the gas. Hydrodynamics predicts that this state can only exist if
the size of the system is larger than the critical size for the stability of the homogeneous cooling state, and expressions
for the hydrodynamic fields in the limit of not too large inhomogeneities can be obtained. The theoretical predictions are
compared with computer simulation results of a system of inelastic hard disks for several values of the coefficient of restitution,
well beyond the quasi-elastic limit. It will be shown that the shear state is indeed exhibited by the system if its size is
larger, but not much larger, than the critical size. The behaviour of the system and the way in which it deviates from the
shear state as its size is increased will also be discussed. 相似文献
16.
Brey JJ Ruiz-Montero MJ Cubero D 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3150-3157
The physical mechanisms leading to the development of density inhomogeneities in a freely evolving low density granular gas are investigated. By means of the direct simulation Monte Carlo method, numerical solutions of the inelastic Boltzmann equation are constructed for both a perturbed system and also for an initially homogeneous state. Analysis of the Fourier components of the fields indicates that the nonlinear coupling contributions of the transversal velocity play a crucial role in the initial setup of clustering. A simple hydrodynamic model is proposed to describe what is observed in the simulations. Finally, the nature of the inhomogeneous state is briefly discussed. 相似文献
17.
S.S. Manna 《Phase Transitions》2013,86(4-5):529-546
Internal avalanches of grain displacements can be created inside a granular material kept in a bin in two ways: (i) by removing a randomly selected grain at the bottom of the bin; and (ii) by breaking a stable arch of grains clogging a hole at the bottom of the bin. Repeated generation of such avalanches leads the system to a steady state. It is relevant to ask whether this state is a critical state, as in self-organized criticality (SOC). We review here some recent studies of this problem using cellular automata and hard-disc models. 相似文献
18.
We investigate the granular flow states in a channel with bottleneck by molecular dynamics simulations.Our study is restricted only on a selected key area rather than on the whole system to focus on the flow properties of a single granular state.A random force field is introduced to control the granular temperature.It is also pointed out that the flow rate in the granular flow can be correlated with the pressure,which leads us to carry out a comprehensive study similar to the classical study for general liquid-gas phase transition.Our results show that the dilute flow state and the dense flow state of the granules are similar to the gas state and the liquid state of general substances,respectively,and the properties of phase transition and critical phenomenon are also similar to those occurring in general substances. 相似文献
19.
A protocol for multipartite quantum clock synchronization is performed under the influence of Unruh thermal noise. The dynamics of multipartite quantum system consisting of Unruh–DeWitt detectors when one of the detectors is accelerated are obtained. To estimate the time difference between the clocks, the time probability is calculated and how the probability is influenced by the Unruh thermal noise and other factors is analyzed. It is shown that both relativistic motion and interaction between the atom and the external scalar field affect the choice of optimal number of excited atoms in the initial state, which leads to a higher clock adjustment accuracy. Time probabilities for different types of initial states approach the same value in the limit of infinite acceleration, while tend to different minimums with increasing number of atoms. In addition, the accuracy of clock synchronization using a pair of entangled clocks in two‐party system is always higher than in a multipartite system, while the optimal Z‐type multipartite initial state always performs better than the W‐type state. 相似文献
20.
We investigate the segregation effect of binary granular mixtures with the same size but different densities under vibration at different air pressures. Our experiments show that the segregation state is seriously dependent on the air pressure and there is a new type of partially segregated state at high air pressure, which has the characteristic that the lighter grains tend to stay at the bottom and form a pure layer, while heavier grains and remained lighter ones tend to rise and to form a mixed layer on the top of the system. We redefine the order parameter to study the variation of the segregation effect with the air pressure and vibration parameter in detail. Finally, the mechanism of the air-driven segregation is illustrated by the faster acceleration due to the airflow through the granular bed for lighter particles. 相似文献