Title: Force Network Response to Vibrations for Grains Jammed in a 2D Hopper

Author (Talk): Carl Merrigan, Brandeis University

Abstract:

Grains falling through a narrow bottleneck may suddenly jam through the formation of an arch of mutually stabilizing grains. For a fixed outlet width, there is a well-defined mean jamming time. However, the process of breaking the arch through vibrations of the walls appears more complex. Instead of a fixed mean time, unjamming may occur immediately or it may take tens to many hundreds of vibration periods. Molecular dynamics simulations make it possible to study how ongoing vertical vibrations of the walls change the internal force network of this jammed solid. Excluding rattlers, the original positions of the grains are approximately fixed until the arch breaks and flow resumes. In contrast, the force network between the grains has a more dramatic, dynamic response to the vibrations. The force network appears to self-organize in order to accommodate the continued injection of additional stresses from the vertical vibrations of the walls. By seeking to characterize the time evolution of forces in this resulting force network, I am seeking to establish the extent to which the structure of the force network correlates with the unjamming time.