Caitano, R. (Rodrigo)

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    Anchoring effect of an obstacle in the silo unclogging process
    (Physical Review Journals, 2023) Caitano, R. (Rodrigo); Garcimartín-Montero, Á. (Ángel); Zuriguel-Ballaz, I. (Iker)
    Contrary to the proven beneficial role that placing an obstacle above a silo exit has in clogging prevention, we demonstrate that, when the system is gently shaken, this passive element has a twofold effect in the clogging destruction process. On one side, the obstacle eases the destruction of weak arches, a phenomenon that can be explained by the pressure screening that it causes in the outlet proximities. But on the other side, we discover that the obstacle presence leads to the development of a few very strong arches. These arches, which dominate in the heavy tailed distributions of unclogging times, correlate with configurations where the number of particles contacting the obstacle from below are higher than the average; hence suggesting that the obstacle acts as an anchoring point for the granular packing. This finding may help one to understand the ambiguous effect of obstacles in the bottleneck flow of other systems, such as pedestrians evacuating a room or active matter in general.
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    Characterization of the clogging transition in vibrated granular media
    (American Physical Society, 2021) Caitano, R. (Rodrigo); Guerrero-Borges, B. V. (Bruno Valdemar); González, R.E.R. (R. E. R.); Zuriguel-Ballaz, I. (Iker); Garcimartín-Montero, Á. (Ángel)
    The existence of a transition from a clogged to an unclogged state has been recently proposed for the flow of macroscopic particles through bottlenecks in systems as diverse as colloidal suspensions, granular matter, or live beings. Here, we experimentally demonstrate that, for vibrated granular media, such a transition genuinely exists, and we characterize it as a function of the outlet size and vibration intensity. We confirm the suitability of the “flowing parameter” as the order parameter, and we find out that the rescaled maximum acceleration of the system should be replaced as the control parameter by a dimensionless velocity that can be seen as the square root of the ratio between kinetic and potential energy. In all the investigated scenarios, we observe that, for a critical value of this control parameter 𝑆𝑐, there seems to be a continuous transition to an unclogged state. The data can be rescaled with this critical value, which, as expected, decreases with the orifice size 𝐷. This leads to a phase diagram in the 𝑆−𝐷 plane in which clogging appears as a concave surface.