Fluctuations affecting granular rheology

Granular flows are susceptible to environmental forcings and fluctuations which may impact their rheologies in complicated ways. Recent advances in kinetic theory have shown that collisional models can explain a range of behavior far wider than the paradigm of the past two decades would suggest. Such models can naturally include the effect of environmental forcings in the energy balance, though may be prohibitively complicated in some circumstances. Simpler empirical models have been proposed to extend the eponymous μ(I) rheology by including the effect of the granular temperature field. Though these constitute a promising first approach to predict directly the effect of induced fluctuations such as environmental forcings, they lack a fundamental basis. Based on discrete element method (DEM) simulations, we establish a direct connection between kinetic theory and these empirical models in order to determine at what point more complicated models are necessary.