Testing Computer Simulation of Granular Flows using Annular Shear Cell
Experiments

By Hayley H. Shen[^1], Daniel M. Hanes[^2], and James T. Jenkins[^3]

**ABSTRACT**

Computational methods provide the opportunity to test parameter space
unattainable under terrestrial laboratory conditions. This feature is
especially important for processing granular materials. Granular
materials are distinctly different from normal fluids. Due to the
particle size, gravity induced body force acting on a particle is
comparable and often exceeds the particle inertia, while for normal
fluids the weight of individual molecules is negligible compared with
the thermal inertia of the molecules. In a flowing granular material the
"viscosity" changes drastically with solid concentration and the local
shear-rate. The rheological properties of a moving granular material are
therefore coupled with the flow field, a feature that is negligible in
regular fluids. In addition, interaction between particles in a granular
flow may include short-range electrostatic forces, and the mechanical
properties of the particles may change due to temperature variations.
The above complications are reasons for consistent higher failures in
processing facilities that deal with granular material rather than
fluids.

To prepare for long-term human operations, first on the Moon and then on
Mars, oxygen and hydrogen must be derived from the local soil. Reliable
equipment for processing granular materials is essential to the
operation. Traditional full-scale physical testing is not possible on
the Earth's surface due to the difference in the gravity field. Before
relying on computational methods, a series of comparisons must be made
with the results of physical experiments. In this talk, we present the
results of physical experiments and computational simulations using an
annular shear cell. In the physical experiments, we use two different
materials, glass and Delrin beads, and several different shear-rates.
The properties of the physical materials and the testing conditions are
the input for the computer simulations.

One major problem in numerical simulation is the time requirement. For
very hard particles the simulation time step is small, lengthening the
total time required. To overcome this problem, we test a series of
Young's moduli, keeping all other parameters the same. It is found that
for dense flows, the behavior of shear and normal stresses in the
simulation are not sensitive to the Young's modulus of the particles.
Using dimensional analysis combined with extrapolation, it is possible
to numerically predict stresses for a wide range of particles. The
simulated stresses for both the glass and the Delrin particles compare
well with those in the physical experiments. This suggests that
computational methods are viable alternatives to physical testing when
designing solid processing equipment.

Submitted to: NASA Workshop on Granular Materials in Lunar and Martian
Exploration, Feb. 2-3, 2005, Orlando, Florida and the John F. Kennedy
Space Center.

[^1]: ^1^ Dept. Civil & Environmental Engineering, Clarkson University,
    Potsdam, NY 13699-5710, <hhshen@clarkson.edu>

[^2]: ^2^ USGS Pacific Science Center, 400 Natural Bridges Drive, Santa
    Cruz CA 95060, <dhanes@usgs.gov>

[^3]: ^3^ Dept. Theoretical & Applied Mechanics, Cornell University,
    Ithaca, NY 14853, [jtj2@cornell.edu](mailto:jisy@clarkson.edu)