Exerting velocity and force on a rigid wall at the same time

Hi LAMMPS USERS
I want to exert both constant velocity and constant pressure (force) to a rigid wall. The schematic model is attached. I used :

velocity RIGID_UP set -0.1 NULL NULL sum yes units box

fix 9 RIGID_UP setforce 0.0 0.0 -{forceup}

My question is:
1- Should I replace “NULL” value in "velocity" command with “0.0”?
2- Does the the 2nd line serve my purpose, If not Is the following couple of commands correct?
fix 9 RIGID_UP setforce 0.0 0.0 0.0
fix 9 RIGID_UP addforce 0.0 0.0 -{forceup}
OR
fix 9 RIGID_UP setforce 0.0 0.0 0.0
fix 9 RIGID_UP aveforce 0.0 0.0 -{forceup}

Thanks in advance.
Rouhollah,1.jpg

Hi LAMMPS USERS
I want to exert both constant velocity and constant pressure (force) to a
rigid wall. The schematic model is attached. I used :
velocity RIGID_UP set -0.1 NULL NULL sum yes units box
fix 9 RIGID_UP setforce 0.0 0.0 -{forceup}

My question is:
1- Should I replace "NULL" value in "*velocity"* command with "0.0"?
2- Does the the 2nd line serve my purpose, If not Is the following couple
of commands correct?
fix 9 RIGID_UP setforce 0.0 0.0 0.0
fix 9 RIGID_UP addforce 0.0 0.0 -{forceup}
OR
fix 9 RIGID_UP setforce 0.0 0.0 0.0
fix 9 RIGID_UP aveforce 0.0 0.0 -{forceup}

please note, that ​this mailing list​ is not an input script approval
service. i suggest you try to act like a true scientist instead and
investigate yourself which of the options serves your requirements best.
you yourself are in the best position to judge, anyway.

axel.

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What you are trying to do is conceptually similar to nano-scratching or friction simulations. In these simulations, the moving parts exert a constant load to the substrate while moving at a constant velocity. This is done in a two-step approach. The first part is to insert the moving part into the substrate at different depths, then for each depth the load experienced from the substrate is measured. From this set of simulations you can obtain a relationship between depth and load, then you can define the depth you need to insert the moving part in to the substrate in order to obtain the desired load. The second step is to start from the above determined depth and configuration, apply a constant velocity to the moving part.

Note this forum does not check your input script nor does it prepare such an input script for you. Please try it out on your own and come back with specific LAMMPS related questions.

Thanks,
Ray

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