This applet requires Pop-Up Windows to be enabled.
Mixing can occur by two mechanisms.
1) For large, freely-flowing, grains, mixing occurs smoothly and steadily
(i.e. with
no variation in the velocity field over time). You can
see this flow by pressing the
'stop' botton, then toggling the 'stick-slip flow' switch
to the 'steady flow' state,
and finally pressing 'restart'.
In this simulation, the yellow curve identifies the shear band
dividing the flowing
grains above from the nearly static bed below. The blue and
red particles are advected
identically with the flow.
Mixing in this case occurs linearly in time.
2) For fine or weakly cohesive grains, mixing occurs erratically, as the
blue shear
band alternately creeps slowly downhill and rapidly slips
back up.
Mixing in this case occurs exponentially rapidly in
time. This exponential behavior
is the hallmark of chaos, and is caused by oscillations
in the flow due to stick-slip
motion of fine or weakly cohesive grains.
For details, see "Spontaneous chaotic granular mixing" Nature
379 (1999) 675-8
(available
online to subscribers).
For non-java capable browsers, animations appear here.
Program notes:
Because particles are initially placed in ordered rows, when they first
emerge
from the flowing layer into the bed, they retain their alignment and appear
as
stripes in the bed. We have chosen not to eliminate this numerical artifact
in this
version.
There is a java bug, possibly due to nonsynchronous multithreading,
that
sometimes causes the control buttons to vanish. Click 'Reload' on your
browser if this occurs.