Clogging-jamming connection in narrow vertical pipes.

We report experimental evidence of clogging due to the spontaneous development of hanging arches when a granular sample composed of spherical particles flows down a narrow vertical pipe. These arches, akin to the ones responsible for silo clogging, can only be possible due to the role of frictional forces; otherwise they will be unstable. We find that, contrary to the silo case, the probability of clogging in vertical narrow tubes does not decrease monotonically with the ratio of the pipe-to-particle diameters.

The role of initial speed in projectile impacts into light granular media.

Projectile impact into a light granular material composed of expanded polypropylene (EPP) particles is investigated systematically with various impact velocities. Experimentally, the trajectory of an intruder moving inside the granular material is monitored with a recently developed non-invasive microwave radar system. Numerically, discrete element simulations together with coarse-graining techniques are employed to address both dynamics of the intruder and response of the granular bed.