unexpected result of sliding motion


I am trying to simulate sliding motion of two solid bodies. Data file, which contains upper body with hemispherical asperity and lower body with flat surface, is read into the input file. The input script that I used is simply modified from ‘in.friction’ which is an example in the lammps package.

The simulation ran without errors, but the result showed unexpected motion.

When I animated the result file, the first frame showed perfect two solid structures which is read from the data file. However, all the atoms mixed together and the solid bodies collapse from second frame to end.

Please advise which part I am missing. Followings are the input script.

I don’t know. When a complex model doesn’t run
as you expect, you have to debug it, and insure
line by line that each command in the input
script is doing what you expect it to do.

You are the best person to do that.


Smaller timestep solved mixing up atoms, and I used fix temp/rescale to set the constant temperature.

This time, I have another problem that the simulation box gets lager than original (mean volume is increasing) in z-direction and the system pressure is decreasing, even though I used fix setforce zero to the boundary.

Can anyone let me know why the fix setforce is not applied?

Thank you,

Sungae Lee

Have you dumped the forces on the atoms and verified
that they are or are not zero? Again, when a complex
model doesn’t do what you expect, you have to

“debug” what is going on. No one else is likely
to do that for you.