Dear Axel,

The following is the very concise explanation of the problem.

I modified LAMMPS in.friction example.

The upper rigid wall is expected to:

1-be rigid (implemented by “fix rigid”)

2- be applied a constant load in “z” direction (by “addforce …” command) and it has to move by time integration in “z”

3- have a constant velocity in “x” (by “velocity set …”)

**But, the upper part doesn’t move in “x” direction. (velocity set command doesn’t work!!!)**

What is wrong here?!

dimension 2

boundary p s p

atom_style atomic

neighbor 0.3 bin

neigh_modify delay 5

########## create geometry

lattice hex 0.9

region box block 0 50 0 22 -0.25 0.25

create_box 4 box

# atom regions

region lo-fixed block INF INF INF 1.1 INF INF

region lo-slab block INF INF INF 7 INF INF

region above-lo block INF INF INF 7 INF INF side out

region hi-fixed block INF INF 20.9 INF INF INF

region hi-slab block INF INF 15 INF INF INF

region below-hi block INF INF 15 INF INF INF side out

create_atoms 1 region lo-slab

create_atoms 1 region hi-slab