Change wall type from servo to velocity controled

Submitted by Rector on Fri, 03/03/2017 - 11:54

Hi,
I am trying to run a triaxial test on a cube shaped sample. I currently inset stl files (3 files for the 3 faces) using the fix_mesh_surface_stress_servo command and another 3 stl files using the fix_mesh_surface_stress command. Once I have finished the consolidation stage of the test, I want to change the top mesh (currently servo controlled) to a non-servo wall so that I can apply a constant velocity to it. Is there a way of doing this?
Many thanks,
Rector

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Laure's picture

Laure | Tue, 03/07/2017 - 10:54

I do it manually: record the position of the servo-controlled wall, then 'unfix' it, then 'fix' your new wall using this position. It introduces a small perturbation due to rounding error, so add a short relaxation time for the system to settle again. To output wall position, check the bottom of the documentation for the fix you use.

variable temp1 equal f_topwall[8]
variable topwallpos equal ${temp1}

Best,
Laure

Rector | Tue, 03/07/2017 - 12:22

I think I will just do it that way. How do you input a mesh to a specified position within the same simulation? The current way I know is to create a mesh that is predefined to the exact position I want it to be at during insertion. However, it would seem to be the case that I would have to perhaps stop the simulation then use a restart command with my new meshes.

BW,
Rector

Rector | Tue, 03/07/2017 - 12:45

Oh yes. I have noticed the move key word. Awesome.
Many thanks Laure.
Regards,
Rector

Zheng Hu | Tue, 10/10/2017 - 18:44

Hi Rector,
I am a newbie using Liggghts and I also want to do a triaxial compression test. But I do have many problems using servo control and some detailed problems. Would it be possible that you send me some clues or codes about your simulations? Many thanks. My email: Zheng.Hu@Colorado.EDU. Looking forward to hear from you.

Zheng Hu | Tue, 10/10/2017 - 19:12

Hi Laure,
I simulated as you suggested, unfix the servo wall first and than replace the same position with another wall. However, when I unfix the servo wall, ERROR will occur: cannot unfix while dump command is active on mesh. Do you know how to solve this problem? Any ideas or suggestions are welcome. Many thanks.
Zheng