Protocol-independent granular temperature supported by numerical simulations

Phys Rev E Stat Nonlin Soft Matter Phys. 2015 Nov;92(5):052201. doi: 10.1103/PhysRevE.92.052201. Epub 2015 Nov 5.

Abstract

A possible approach to the statistical description of granular assemblies starts from Edwards's assumption that all blocked states occupying the same volume are equally probable [Edwards and Oakeshott, Physica A 157, 1080 (1989)]. We performed computer simulations using two-dimensional polygonal particles excited periodically according to two different protocols: excitation by pulses of "negative gravity" and excitation by "rotating gravity." The first protocol exhibits a nonmonotonous dependency of the mean volume fraction on the pulse strength. The overlapping histogram method is used in order to test whether the volume distribution is described by a Boltzmann-like distribution and to calculate the inverse compactivity as well as the logarithm of the partition sum. We find that the mean volume is a unique function of the measured granular temperature, independently of the protocol and of the branch in ϕ(g), and that all determined quantities are in agreement with Edwards's theory.