Change servo controlled wall to velocity controlled wall

Submitted by Zheng Hu on Thu, 10/12/2017 - 05:37

Dear all,

I am doing a triaxial compression test using LIGGGHTS. First, I applied six servo controlled wall using command: fix mesh/surface/stress/servo to execute a confining pressure on a cube soil specimen. After this process, I want to execute a constant velocity on the walls instead of a target force on the servo walls. This means I may need to change the servo controlled wall to velocity controlled wall.

I now have a complicated method to make it. First, unfix "fix mesh/surface/stress/servo", Second, fix a new wall using"fix mesh/surface/stress", Third, apply this command "fix move/mesh" to move the wall.

Does anybody have some better ideas to realize this condition?

Many thanks.
Zheng

Forums:

ARPITA RAY | Sat, 07/15/2023 - 17:36

Hi Zheng,
I am trying to do a similar thing but by this method the meshes of the walls are losing their stress history, that is, the stresses on the walls after servo operation vanish as soon as we unfix it. Could you figure out anything other way to change servo walls to velocity controlled walls? if yes, can you please share and help me out?
Thanks,
Arpita

agupta87 | Wed, 08/30/2023 - 01:26

I actually have done this - one can use velocity verlet integration with velocity/displacement controlled walls to make this happen. I can upload/link you to relevant code if you still need help.