The phenomenon of unblocking, under study at the university

Physics reveals that solid bodies have the property of getting stuck when they are forced to pass through a constriction, producing an arc that plugs the exit. A common example is the stampede of people in multitudinous events or the discharge of industrial silos. Bruno Guerrero (Venezuela, 33 years old) has studied clogging phenomena in his doctoral thesis and has delved into how vibration affects the stability of the arches that obstruct the exit of a silo.

The work developed by Guerrero and collaborators is the first experimental research that analyzes the dynamics of long-lasting jams and has worked with a prototype of an industrial silo. "Our silo is a two-dimensional transparent container that resembles an hourglass, filled with spheres and anchored to an electromagnetic stirrer that is able to provide a controlled vibration. With the help of a camera, the region where the clogging occurs is recorded and, through image processing, the arc responsible for the blockage is identified over time," notes the researcher.

The main conclusion of this research is that, when jamming occurs, the arches follow intermittent dynamics and gradually deform by adopting different configurations. "Regardless of the vibration intensity applied, the perturbation tends to destabilize the arches, even for those that resist vibration. And while the initial shape of the arch affects its stability, it is the successive deformations that ultimately dictate its outcome."

Another result of this study is that arches that do not break - despite vibration - do not have any dynamic or structural characteristics that differentiate them from those in which vibration facilitates unblocking. On the other hand, "long-lasting arches show clear signs of aging: memory effects persist and relaxation slows with the passage of time".

Bruno Guerrero believes that the studies of clogging performed in granular media can be extrapolated to more complex situations such as the obstructions that occur in colloids (for example, the formation of microthrombi in myocardial capillaries) or in active matter (bacterial colonies, herds of animals, vehicular traffic or autonomous robots) when passing through narrow channels.

Bruno Guerrero continues his research on the unclogging phenomenon, in particular the transition to clogging, and its dependence on the discharge hole and the characteristics of the applied vibration.

Bibliographical references

- B.V. Guerrero, B. Chakraborty, I. Zuriguel, A. Garcimartín; (2019) Nonergodicity in silo unclogging: Broken and unbroken arches Phys. Rev. E 100, 032901. DOI: 10.1103/PhysRevE.100.032901

- B.V. Guerrero, L.A. Pugnaloni, C. Lozano, I. Zuriguel, A. Garcimartín; (2018) Slow relaxation dynamics of clogs in a vibrated granular silo, Phys. Rev. E 97, 042904. DOI: 10.1103/PhysRevE.97.042904