Abstract

Clogging phenomenon -broadly defined as the arrest of the flow of macroscopic bodies due to the formation of a local structure (known as an arch, that carries the whole system to a state of rest)- is a fascinating example where local structures (of a few particles) trigger the large-scale spatio-temporal bulk patterns (as the macroscopic flow).

Here, we present our experimental findings [1,2] on the unclogging phenomenon in a silo with a narrow outlet (which barely exceeds the particles’ diameter by a few units), filled with rigid and frictional spheres, and submitted to low-intensity vibration. Based solely on experimental measurements from the particle trajectories of the arch and some time variables, we described the dynamics in terms of two morphological arch variables. Arches exhibit jerking dynamics where plastic deformations of the arch structure are interspersed with quiescent periods. The geometrical frustration hinders the free displacement between different configurations, leading to subdiffusion. We characterized (in statistical terms) the stability of arches against a gentle external perturbation and some diffusive properties, and quantified the ergodicity breaking (a signature of aging). Finally, all the exposed results are rationalized through a subdiffusive Continuous-Time Random Walk-like model.

[1] B. V. Guerrero, L. A. Pugnaloni, C. Lozano, I. Zuriguel, and A. Garcimartín (2018). Slow relaxation dynamics of clogs in a vibrated granular silo. Physical Review E 97(4), 042904.

[2] B. V. Guerrero, B. Chakraborty, B., I. Zuriguel, and A. Garcimartı́n (2019). Nonergodicity in silo unclogging: Broken and unbroken arches. Physical Review E 100(3): 032901