  The Discrete Element Method (DEM) is frequently used to model complex
granular systems and to augment the knowledge that we obtain through theory,
experimentation, and real-world observations. Numerical simulations are a
particularly powerful tool for studying the regolith-covered surfaces of
asteroids, comets, and small moons, where reduced-gravity environments produce
ill-defined flow behaviors. In this work, we present a method for validating
soft-sphere DEM codes for both terrestrial and small-body granular
environments. The open-source code Chrono is modified and evaluated first with
a series of simple two-body-collision tests, and then, with a set of piling and
tumbler tests. In the piling tests, we vary the coefficient of rolling friction
to calibrate the simulations against experiments with 1 mm glass beads. Then,
we use the friction coefficient to model the flow of 1 mm glass beads in a
rotating drum, using a drum configuration from a previous experimental study.
We measure the dynamic angle of repose, the flowing layer thickness, and the
flowing layer velocity for tests with different particle sizes, contact force
models, coefficients of rolling friction, cohesion levels, drum rotation speeds
and gravity levels. The tests show that the same flow patterns can be observed
at Earth and reduced-gravity levels if the drum rotation speed and the
gravity-level are set according to the dimensionless parameter known as the
Froude number. Chrono is successfully validated against known flow behaviors at
different gravity and cohesion levels, and will be used to study small-body
regolith dynamics in future works.
