Two-dimensional packing in prolate granular materials

Abstract

We investigate the two-dimensional packing of extremely prolate (aspect ratio α = L/D > 10) granular materials, comparing experiments with Monte-Carlo simulations. In experimental piles of particles with aspect ratio α = 12 we find the average packing fraction to be 0.68±0.03. Both experimental and simulated piles contain a large number of horizontal particles, and particle alignment is quantified by an orientational order correlation function. In both simulation and experiment the correlation between particle orientation decays after a distance of two particle lengths. It is possible to identify voids in the pile with sizes ranging over two orders of magnitude. The experimental void distribution function is a power law with exponent −β = −2.37 ± 0.05. Void distributions in simulated piles do not decay as a power law, but do show a broad tail. We extend the simulation to investigate the scaling at very large aspect ratios. A geometric argument predicts the pile number density to scale as α −2 . Simulations do indeed scale this way, but particle alignment complicates the picture, and the actual number densities are quite a bit larger than predicted.

Column collapse of granular rods

“…In Figure 4 we plot the collapse probability as a function of this order parameter H for all of our data, encompassing the complete range of aspect ratios that collapse (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and two different particle diameters. Figure 4 shows that, when scaled as per Eq.…”

“…Lumay and Vandewalle subsequently [11] used a two-dimensional experiment to highlight the importance of rotation in rod rearrangements. Blouwolff and Fraden [12] investigated the contact number in 3d packings, and Stokely et al [13] looked at static properties of 2d packings. Pournin et al [14,15] have written discrete element method (DEM) simulations of spherocylindrical particles that show crystallization and ordering under various excitations.…”

Spontaneous Patterning of Confined Granular Rods

“…Such driven dissipative systems, however, are far from equilibrium and need not evolve to states of maximal configurational entropy. For example, prior studies utilizing macroscopic rods focused on jammed or other metastable states [3,4].Here, we report on finite-sized driven dissipative granular systems of rods in steady-state that share many properties of lyotropic liquid crystals at equilibrium. We find that short ranged hard core interactions determine the arrangement of the moving rods for all densities.…”

“…Such driven dissipative systems, however, are far from equilibrium and need not evolve to states of maximal configurational entropy. For example, prior studies utilizing macroscopic rods focused on jammed or other metastable states [3,4].…”

Creating and Transporting Trojan Wave Packets

“…The circular wave packets employed here are prepared, as described elsewhere [4], by first creating a mix of quasi-1D potassium Rydberg atoms with n i ¼ 304 and 306 oriented along the x axis by direct photoexcitation of selected redshifted Stark states in the presence of a weak ($ 400 V cm À1 ) dc field [19]. This field is then turned off and a transverse electric pump field F pump y is suddenly applied along the Ày axis creating a wave packet that undergoes Stark precession [20,21].…”