Molecular dynamics studies of granular flow through an aperture

Abstract

Molecular dynamics methods are used to study two-dimensional gravity-driven granular flow through a horizontal aperture. Two distinct approaches to modeling the granular particles are studied. ͑a͒ Circular particles subject to a strongly repulsive short-range interaction, together with normal and tangential frictional damping forces. ͑b͒ Rigid nonconvex particles, each consisting of disks arranged as an equilateral triangle, suitably spaced to provide a tangible indentation along each edge; the same repulsive interactions between disks in different grains and normal frictional damping forces are incorporated, but transverse damping is omitted, with the model relying on grain shape to resist sliding motion. In order to allow accurate measurements under steady-state conditions, a continuous-feed approach is adopted, in which grains exiting through the hole are returned to the top of the material in the container. For both models the output flow is measured as a function of aperture size, and the observed behavior is compared with previous theoretical and experimental results. Tests of the degree to which the models reproduce the depth independence of the flow are reported, and the influence of the container width and the nature of the walls are studied. The depth dependence of the pressure, the local stress distribution, and the particle flow patterns are also examined.

Granular flow from a silo: Discrete-particle simulations in three dimensions

“…There is an enormous variety of problems, some of which have proved more tractable from a simulational point of view than others. The present paper reports the use of molecular dynamics techniques in studying a version of the silo outflow problem in three dimensions; this work represents an extension of earlier work that dealt with the corresponding two-dimensional problem [4], a choice dictated by computational feasibility at the time. Earlier references dealing with two-dimensional simulations are [5,6], and the three-dimensional case has been discussed in [7].…”

The flow rate of granular materials through an orifice

“…(1) can be easily derived for the two-dimensional case and a flow dependence on the diameter of the silo of D 3/2 0 is obtained. The Beverloo law, and particularly the 5/2 power dependence of the flow rate on the diameter of the orifice, has been found to be robust for different kind of particles, independently of their packing fraction, density, surface properties or shape [7,8] …”

Micro instabilities in a system of particles in silos during filling process

“…There has been a number of models introduced to describe the granular medium in a silo, including continuummechanics models (Janssen 1895;Bouchard et al 1995;Ragneau and Aribert 1993), ®nite element analysis (Ooi and She 1997; Meng et al 1997), statistical analysis (Chen et al 1996), cellular automata models (Claudin and Bouchard 1997), and molecular dynamics models (Ristow and Herrmann 1995;Sakaguchi et al 1993;Hirshfeld et al 1997;Rong et al 1997). The experimental work on stress distribution in silos has also been done (Connelly 1983;Eibl 1984;Jarrett et al 1996;Tejchman and Gudehus 1993).…”