Reducing Clogging Probability in Granular Flow with a Movable Obstacle

The rate of discharge of grains through a bulk container, like a hopper or silo, is controlled by the size of the opening, and when this becomes very small, the flow can clog. Counterintuitively, it has been shown in 2D studies that a stationary obstruction placed near the outlet of the container can reduce the probability of clogging. A recent 3D experimental and computational study of gravity driven flow in a tapered hopper showed that a well-placed obstacle can reduce clogging in 3D as well. [1] This study showed that this phenomenon occurs for both spherical and rod-like obstacles, and the dominant mechanism is geometric in nature. Using LAMMPS simulations, we allow a spherical  obstacle in a  hopper geometry to oscillate in the horizontal plane under a harmonic central potential. We observe for particular force constants that clogging probability is significantly reduced compared to the rigid case, increasing mass flow and time duration between clogs. We further examine the effect of a spherical obstacle in a flat-bottomed cylindrical container to understand how this mechanism extends to other geometries. 

[1] Sinha et al., Phys. Rev. Lett. 135, 178201 (2025).