[lammps-users] the velocity profile problem of the shear example

Dear Lammps Users,

The shear example (lammps-24Sep10/examples/shear) was repeated. To fully understand the velocity profile of the mobile layer, the boundary was changed to the periodic condition and the running time was increased. For the output, we used “fix ave/spatial” ( fix 4) and/or “fix ave/atom” (fix 5 and 6). The velocity profile of the mobile layer we got is very nice like a LJ fluid (yes, it is). But the max velocity in the profile is about 3.56, much higher than the velocity of the upper layer, v=1. There might be something wrong with my output orders. Please help to get the correct velocity profile of the mobile layer. Thanks a lot.

here is my input file:

How do you shear something that is periodic? Are you trying
to get a V-shaped velocity profile? Have you tried visualizing
your system? Is it doing what you expect? I presume fix ave/spatial
is doing exactly what you told it to do - so you ought to be
able to figure out why it is giving the answers it does from
your data, e.g. dump the velocities to a dump file.


Thanks for your quick response.
Dr. Bohumir Jelinek from CAVS of Mississippi State University located the problem and provided a straight answer as follow: