FRLP - I+D+i - GRUPOS UTNhttp://hdl.handle.net/123456789/17442019-07-17T02:48:10Z2019-07-17T02:48:10ZClogging transition of many particle systems flowing through bottleneckshttp://hdl.handle.net/123456789/28312019-02-04T19:31:16Z2014-01-01T00:00:00ZClogging transition of many particle systems flowing through bottlenecks
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.
2014-01-01T00:00:00ZArch based configurations in the volume ensemble of static granular systemshttp://hdl.handle.net/123456789/28302019-02-04T19:32:36Z2015-01-01T00:00:00ZArch based configurations in the volume ensemble of static granular systems
We propose an alternative approach to count the microscopic static configurations of granular packs under gravity by considering arches. This strategy obviates the problem of filtering out configurations that are not mechanically stable, opening the way for a range of granular models to be studied via ensemble theory. Following this arch-based approach, we have obtained the exact density of states for a 2D, non-interacting rigid arch model of granular assemblies. The calculated arch size distribution and volume fluctuations show qualitative agreement with realistic simulations of tapped granular beds. We have also validated our calculations by comparing them with the analytic solution for the limiting case of a quasi-1D column of frictionless disks.
2015-01-01T00:00:00ZStructure of force networks in tapped particulate systems of disks and pentagons II Persistence analysishttp://hdl.handle.net/123456789/28292019-02-04T19:31:02Z2016-01-01T00:00:00ZStructure of force networks in tapped particulate systems of disks and pentagons II Persistence analysis
In the companion paper [Pugnaloni et al., Phys. Rev. E 93, 062902 (2016)], we use classical measures based on force probability density functions (PDFs), as well as Betti numbers (quantifying the number of components, related to force chains, and loops), to describe the force networks in tapped systems of disks and pentagons. In the present work, we focus on the use of persistence analysis, which allows us to describe these networks in much more detail. This approach allows us not only to describe but also to quantify the differences between the force networks in different realizations of a system, in different parts of the considered domain, or in different systems. We show that persistence analysis clearly distinguishes the systems that are very difficult or impossible to differentiate using other means. One important finding is that the differences in force networks between disks and pentagons are most apparent when loops are considered: the quantities describing properties of the loops may differ significantly even if other measures (properties of components, Betti numbers, force PDFs, or the stress tensor) do not distinguish clearly or at all the investigated systems.
2016-01-01T00:00:00ZExperimental proof of faster is slower in systems of frictional particles flowing through constrictionshttp://hdl.handle.net/123456789/28282019-02-04T19:30:28Z2015-01-01T00:00:00ZExperimental proof of faster is slower in systems of frictional particles flowing through constrictions
The “faster-is-slower” (FIS) effect was first predicted by computer simulations of the egress of pedestrians through a narrow exit [D. Helbing, I. J. Farkas, and T. Vicsek, Nature (London) 407, 487 (2000)]. FIS refers to the finding that, under certain conditions, an excess of the individuals' vigor in the attempt to exit causes a decrease in the flow rate. In general, this effect is identified by the appearance of a minimum when plotting the total evacuation time of a crowd as a function of the pedestrian desired velocity. Here, we experimentally show that the FIS effect indeed occurs in three different systems of discrete particles flowing through a constriction: (a) humans evacuating a room, (b) a herd of sheep entering a barn, and (c) grains flowing out a 2D hopper over a vibrated incline. This finding suggests that FIS is a universal phenomenon for active matter passing through a narrowing.
2015-01-01T00:00:00Z