37 research outputs found
Quasi-rigidity: some uniqueness issues
Quasi-rigidity means that one builds a theory for assemblies of grains under
a slowly changing external load by using the deformation of those grains as a
small parameter. Is quasi-rigidity a complete theory for these granular
assemblies? Does it provide unique predictions of the assembly's behavior, or
must some other process be invoked to decide between several possibilities? We
provide evidence that quasi-rigidity is a complete theory by showing that two
possible sources of indeterminacy do not exist for the case of disk shaped
grains. One possible source of indeterminacy arises from zero-frequency modes
present in the packing. This problem can be solved by considering the
conditions required to obtain force equilibrium. A second possible source of
indeterminacy is the necessity to choose the status (sliding or non-sliding) at
each contact. We show that only one choice is permitted, if contacts slide only
when required by Coulomb friction.Comment: 14 pages, 3 figures, submitted to Phys Rev E (introduction and
conclusion revised
Understanding the dynamics of segregation bands of simulated granular material in a rotating drum
Axial segregation of a binary mixture of grains in a rotating drum is studied
using Molecular Dynamics (MD) simulations. A force scheme leading to a constant
restitution coefficient is used and shows that axial segregation is possible
between two species of grains made of identical material differing by size.
Oscillatory motion of bands is investigated and the influence of the frictional
properties elucidated. The mechanism of bands merging is explained using direct
imaging of individual grains
Continuous Avalanche Segregation of Granular Mixtures in Thin Rotating Drums
We study segregation of granular mixtures in the continuous avalanche regime
(for frequencies above ~ 1 rpm) in thin rotating drums using a continuum theory
for surface flows of grains. The theory predicts profiles in agreement with
experiments only when we consider a flux dependent velocity of flowing grains.
We find the segregation of species of different size and surface properties,
with the smallest and roughest grains being found preferentially at the center
of the drum. For a wide difference between the species we find a complete
segregation in agreement with experiments. In addition, we predict a transition
to a smooth segregation regime - with an power-law decay of the concentrations
as a function of radial coordinate - as the size ratio between the grains is
decreased towards one.Comment: 4 pages, 4 figures, http://polymer.bu.edu/~hmaks
Size Segregation and Convection of Granular Mixtures Almost Completely Packed in the Rotating Thin Box
Size segregation of granular mixtures which are almost completely packed in a
rotating drum is discussed with an effective simulation and a brief analysis.
Instead of a 3D drum, we simulate 2D rotating thin box which is almost
completely packed with granular mixtures. The phase inversion of radially
segregated pattern which was found in a 3D experiment are qualitatively
reproduced with this simulation, and a brief analysis is followed. Moreover in
our simulation, a global convection appears after radial segregation pattern is
formed, and this convection induces axially segregated pattern.Comment: 9 pages, 5 figures, PACS number(s): 45.70.-n, 45.70.M