Nicolas, A.; Garcimartín-Montero, Á. (Ángel); Zuriguel-Ballaz, I. (Iker). "Trap model for clogging and unclogging in granular hopper flows". Physical Review Letters. 120 (19), 2018, 198002
Granular flows through narrow outlets may be interrupted by the formation of arches or vaults that clog
the exit. These clogs may be destroyed by vibrations. A feature which remains elusive is the broad
distribution pð¿Þ of clog lifetimes ¿ measured under constant vibrations. Here, we propose a simple model
for arch breaking, in which the vibrations are formally equivalent to thermal fluctuations in a Langevin
equation; the rupture of an arch corresponds to the escape from an energy trap. We infer the distribution of
trap depths from experiments made in two-dimensional hoppers. Using this distribution, we show that the
model captures the empirically observed heavy tails in pð¿Þ. These heavy tails flatten at large ¿, consistently
with experimental observations under weak vibrations. But, here, we find that this flattening is systematic,
which casts doubt on the ability of gentle vibrations to restore a finite outflow forever. The trap model also
replicates recent results on the effect of increasing gravity on the statistics of clog formation in a static silo.
Therefore, the proposed framework points to a common physical underpinning to the processes of clogging
and unclogging, despite their different statistics.