Facultad de Ciencias

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Author search.filters.author.Guerrero-Borges, B. V. (Bruno Valdemar)Subject search.filters.subject.Granular flow

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    On the broad tails in breaking time distributions of vibrated clogging arches
    (2021) Barbosa-da-Silva, R.C. (Rodrigo C.); Zuriguel-Ballaz, I. (Iker); Nicolas, A. (Alexandre); Montero, Á. (Ángel); Guerrero-Borges, B. V. (Bruno Valdemar)
    Flowing grains can clog an orifice by developing arches, an undesirable event in many cases. Several strategies have been put forward to avoid this. One of them is to vibrate the system in order to undo the clogging. Nevertheless, the time taken to break an arch under a constant vibration has a distribution displaying a heavy tail. This can lead to a situation where the average breaking time is not well defined. Moreover, it has been observed in some experiments that these tails tend to flatten for very long times, exacerbating the problem. Here we will review two conceptual frameworks that have been proposed to understand the phenomenon and discuss their physical implications.
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    Slow relaxation dynamics of clogs in a vibrated granular silo
    (2018) Pugnaloni, L.A. (Luis A.); Zuriguel-Ballaz, I. (Iker); Montero, Á. (Ángel); Lozano, C. (Carmen); Guerrero-Borges, B. V. (Bruno Valdemar)
    We experimentally explore the vibration-induced unclogging of arches halting the flow in a two-dimensional silo. The endurance of arches is determined by carrying out a survival analysis of their breaking times. By analyzing the dynamics of two morphological variables, we demonstrate that arches evolve toward less regular structures and it seems that there may exist a certain degree of irregularity that the arch reaches before collapsing. Moreover, we put forward that ¿ (the standard deviation of all angles between consecutive beads) describes faithfully the morphological evolution of the arch. Focusing on long-lasting arches, we study ¿ calculating its two-time autocorrelation function and its mean-squared displacement. In particular, the apparent logarithmic increase of the correlation and the decrease of the mean-squared displacement of ¿ when the waiting time is increased reveal a slowing down of the dynamics. This behavior is a clear hallmark of aging phenomena and confirms the lack of ergodicity in the unclogging dynamics. Our findings provide new insights on how an arch tends to destabilize and how the probability that it breaks with a long sustained vibration decreases with time.