The effect of the packing fraction on the jamming of granular flow through small apertures

Uñac, Rodolfo Omar; Vidales, Ana María; Pugnaloni, Luis A.

doi:10.1088/1742-5468/2012/04/p04008

Cited by 17 publications

(12 citation statements)

References 38 publications

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“…Only a careful preparation of the initial φ before the very first burst might be controlled (see Ref. 41 ). Of course, it is expected that a system with extremely low packing fraction will never develop clogging, but in this case the value of C L at the bottleneck will also approach zero.…”

Section: Discussion/conclusionmentioning

confidence: 99%

Clogging transition of many-particle systems flowing through bottlenecks

Zuriguel

Parisi

Hidalgo

et al. 2014

Sci Rep

292

287

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When a large set of discrete bodies passes through a bottleneck, the flow may become intermittent due to the development of clogs that obstruct the constriction. Clogging is observed, for instance, in colloidal suspensions, granular materials and crowd swarming, where consequences may be dramatic. Despite its ubiquity, a general framework embracing research in such a wide variety of scenarios is still lacking. We show that in systems of very different nature and scale -including sheep herds, pedestrian crowds, assemblies of grains, and colloids- the probability distribution of time lapses between the passages of consecutive bodies exhibits a power-law tail with an exponent that depends on the system condition. Consequently, we identify the transition to clogging in terms of the divergence of the average time lapse. Such a unified description allows us to put forward a qualitative clogging state diagram whose most conspicuous feature is the presence of a length scale qualitatively related to the presence of a finite size orifice. This approach helps to understand paradoxical phenomena, such as the faster-is-slower effect predicted for pedestrians evacuating a room and might become a starting point for researchers working in a wide variety of situations where clogging represents a hindrance.

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Section: Discussion/conclusionmentioning

confidence: 99%

Clogging transition of many-particle systems flowing through bottlenecks

Zuriguel

Parisi

Hidalgo

et al. 2014

Sci Rep

292

287

View full text Add to dashboard Cite

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“…Of more direct relevance for our work is the study of intermittency in the mass discharge rate. For example, Uñac and co-workers found both fluctuations and characteristic time scales growing with decreasing hole size [34]. However, Janda and co-authors found no such behavior [35].…”

Section: Prior Experimentsmentioning

confidence: 99%

Intermittency and velocity fluctuations in hopper flows prone to clogging

Thomas

Durian

2016

Phys. Rev. E

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We study experimentally the dynamics of granular media in a discharging hopper. In such flows, there often appears to be a critical outlet size D c such that the flow never clogs for D > D c . We report on the time-averaged velocity distributions, as well as temporal intermittency in the ensemble-averaged velocity of grains in a viewing window, for both D < D c and D > D c , near and far from the outlet. We characterize the velocity distributions by the standard deviation and the skewness of the distribution of vertical velocities. We propose a measure for intermittency based on the two-sample Kolmogorov-Smirnov D KS statistic for the velocity distributions as a function of time. We find that there is no discontinuity or kink in these various measures as a function of hole size. This result supports the proposition that there is no well-defined D c and that clogging is always possible. Furthermore, the intermittency time scale of the flow is set by the speed of the grains at the hopper exit. This latter finding is consistent with a model of clogging as the independent sampling for stable configurations at the exit with a rate set by the exiting grain speed [C. C. Thomas We study experimentally the dynamics of granular media in a discharging hopper. In such flows, there often appears to be a critical outlet size D c such that the flow never clogs for D > D c . We report on the time-averaged velocity distributions, as well as temporal intermittency in the ensemble-averaged velocity of grains in a viewing window, for both D < D c and D > D c , near and far from the outlet. We characterize the velocity distributions by the standard deviation and the skewness of the distribution of vertical velocities. We propose a measure for intermittency based on the two-sample Kolmogorov-Smirnov D KS statistic for the velocity distributions as a function of time. We find that there is no discontinuity or kink in these various measures as a function of hole size. This result supports the proposition that there is no well-defined D c and that clogging is always possible. Furthermore, the intermittency time scale of the flow is set by the speed of the grains at the hopper exit. This latter finding is consistent with a model of clogging as the independent sampling for stable configurations at the exit with a rate set by the exiting grain speed [C. C. Thomas and D.

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“…In our case the silo is emptied and refilled with the aperture closed, which is opened only after the grains are static. Uñac et al [12] have conducted a similar type of protocol as the one used here, but the system is tapped before opening the aperture to achieve a desired initial packing fraction. They found that clogging maw vary dramatically depending on the initial packing fraction before starting the avalanche.…”

Section: Resultsmentioning

confidence: 99%

Effect of grain shape on the jamming of two-dimensional silos

2017

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We present discrete element method simulations of the discharge of silos in two dimensions. We study the effect of the grain shape on the clogging of small apertures, considering regular polygons and disks of equal mass. In particular, we analyze the avalanche size distribution and the jamming probability for disks, triangles, squares, pentagons, hexagons and heptagons as a function of the aperture size. We show that the jamming probability presents a non-linear response as a function of the number of vertexes of the polygons.

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The effect of the packing fraction on the jamming of granular flow through small apertures

Cited by 17 publications

References 38 publications

Clogging transition of many-particle systems flowing through bottlenecks

Clogging transition of many-particle systems flowing through bottlenecks

Intermittency and velocity fluctuations in hopper flows prone to clogging

Effect of grain shape on the jamming of two-dimensional silos

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