Dynamical fluctuations in dense granular flows

Gardel, Emily; Sitaridou, E.; Facto, Kevin; Keene, Ellen; Hattam, Kelsey; Easwar, Nalini; Menon, Narayanan

doi:10.1098/rsta.2009.0189

Cited by 45 publications

(59 citation statements)

References 18 publications

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“…Since the early experimental work in a granular Couette geometry by Miller et al (see [36]), force fluctuations in sheared granular materials received a great attention in the past recent years by analysing force fluctuations on objects moving in a static granular medium [8,10,37] or the force at the boundary of a granular flow during silo discharge [38,39]. Some studies directly tracked the force fluctuations between particles in response to an external perturbation [40].…”

Section: Discussionmentioning

confidence: 99%

Numerical investigations of the force experienced by a wall subject to granular lid-driven flows: regimes and scaling of the mean force

et al. 2015

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Discrete element simulations are used to model a two-dimensional gravity-free granular sample, which is trapped between two smooth sidewalls and one bottom rough wall while being subject to a constant shearing velocity at the top under a given confinement pressure. This system, inspired by conventional fluid mechanics, is called a granular liddriven cavity. Attention is firstly paid to the time-averaged dynamics of the grains once a steady-state is reached. Strong spatial heterogeneities associated with a large-scale vortex formed within the whole volume of the lid-driven cavity are observed. The mean steady force on the sidewall facing the shearing velocity is then investigated in detail for different cavity lengths, shearing velocities and confinement pressures at the top. The ratio of the force on the latter wall to the top confinement pressure force is not constant but depends on both the shearing velocity and the confinement pressure. Above a critical value of the cavity length relative to the wall height and over a wide range of both shearing velocity and top confinement pressure, all data merge into a one-to-one relation between the mean force scaled by the top pressure force and the macroscopic inertial number of the lid-driven cavity. This result reveals the key role played by the inertial rheology of the granular material in the granular force transmission.

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Section: Discussionmentioning

confidence: 99%

Numerical investigations of the force experienced by a wall subject to granular lid-driven flows: regimes and scaling of the mean force

et al. 2015

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“…As discussed previously [11,12,20], the formation of transient force chains during hopper flow is related to the stick-slip events of hopper flow, which in turn control the flow rate and rheology. Hence, we expect that a larger probability of forming long-lived force chains (e.g.…”

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confidence: 99%

“…Most recent results from [8] imply that all hoppers have a nonzero probability to clog. Other studies [10][11][12][13][14][15] have also sought to understand flow and clogging (or jamming) mechanisms from a microscopic viewpoint. However, for simplicity, theories developed from the above studies often tend to assume spherical particles, including disks in two dimensions (2D).…”

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confidence: 99%

Orientation, flow, and clogging in a two-dimensional hopper: Ellipses vs. disks

Tang

Behringer

2016

EPL

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-Two-dimensional (2D) hopper flow of disks has been extensively studied. Here, we investigate hopper flow of ellipses with aspect ratio α = 2, and we contrast that behavior to the flow of disks. We use a quasi-2D hopper containing photoelastic particles to obtain stress/force information. We simultaneously measure the particle motion and stress. We determine several properties, including discharge rates, jamming probabilities, and the number of particles in clogging arches. For both particle types, the size of the opening, D, relative to the size of particles, is an important dimensionless measure. The orientation of the ellipses plays an important role in flow rheology and clogging. The alignment of contacting ellipses enhances the probability of forming stable arches. This study offers insight for applications involving the flow of granular materials consisting of ellipsoidal shapes, and possibly other non-spherical shapes.Hopper flows of granular materials involve dynamical granular states with important industrial applications [1,2]. Time-averaged granular flow theories, often using hopper flow as a test case, have progressed from continuum mechanics models to mesoscopic models [2][3][4][5][6]. Fluctuations and clogging (or jamming) are also important characteristics for hopper flow. Experiments [7][8][9] have examined the the clogging transition of hopper flow for different grain properties and hopper geometries. Most recent results from [8] imply that all hoppers have a nonzero probability to clog. Other studies [10][11][12][13][14][15] have also sought to understand flow and clogging (or jamming) mechanisms from a microscopic viewpoint. However, for simplicity, theories developed from the above studies often tend to assume spherical particles, including disks in two dimensions (2D). The effect of particle shape on hopper flow is usually not their focus. In reality, particle shapes are often not spherical; rice and M&M's are roughly ellipsoids; sand particles have irregular shapes. Thus, it is scientifically and industrially relevant to explore how particle shape affects flow rheology and clogging mechanisms.A simple way to explore particle shape effects is to contrast 2D hopper flows of disks and ellipses for the time-averaged discharge rate,Ṁ , and jamming probability. Discharge rates of hopper flow often follow the wellestablished Beverloo equation [16], which relatesṀ to the hopper opening size, D :Ṁ ∝ (D − kd avg ) (n−1/2) , where n is the spatial dimension (e.g. n = 2 or 3 for two or three-dimensional systems). D is reduced by kd avg due to boundary effects, where d avg characterizes the grain size, and k is an order-one constant [2]. Recent studies [17,18] have provided micromechanical insights into this equation with a coarse-grain technique. An important open question concerns the relevance of this relation for non-spherical particles. Several studies have used DEM simulation methods to understand how the aspect ratio of an ellipse could affect the discharge rate [21][22][23][24][25][26][...

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“…A particular hallmark of such a framework is the transition towards fluctuation distributions far from Gaussian, usually characterized by long tails, that depict slow structural relaxations within such arrested systems [8][9][10][11][12][13]. Different models have been proposed to reproduce these observations [14,15].…”

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confidence: 99%

Diffusive and Arrestedlike Dynamics in Currency Exchange Markets

et al. 2017

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This work studies the symmetry between colloidal dynamics and the dynamics of the Euro-U.S. dollar currency exchange market (EURUSD). We consider the EURUSD price in the time range between 2001 and 2015, where we find significant qualitative symmetry between fluctuation distributions from this market and the ones belonging to colloidal particles in supercooled or arrested states. In particular, we find that models used for arrested physical systems are suitable for describing the EURUSD fluctuation distributions. Whereas the corresponding mean-squared price displacement (MSPD) to the EURUSD is diffusive for all years, when focusing in selected time frames within a day, we find a two-step MSPD when the New York Stock Exchange market closes, comparable to the dynamics in supercooled systems. This is corroborated by looking at the price correlation functions and non-Gaussian parameters and can be described by the theoretical model. We discuss the origin and implications of this analogy.

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Dynamical fluctuations in dense granular flows

Cited by 45 publications

References 18 publications

Numerical investigations of the force experienced by a wall subject to granular lid-driven flows: regimes and scaling of the mean force

Numerical investigations of the force experienced by a wall subject to granular lid-driven flows: regimes and scaling of the mean force

Orientation, flow, and clogging in a two-dimensional hopper: Ellipses vs. disks

Diffusive and Arrestedlike Dynamics in Currency Exchange Markets

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