Servo wall, triaxial test

Submitted by Rahul Kumar on Tue, 01/21/2020 - 12:31

While doing Triaxial test. I have first applied confining pressure (200k) on all 6 wall and then applied fix modify command to modify the target value for top and bottom wall so that additional deviator stress can be applied.

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fix twall_servo all mesh/surface/stress/servo file meshes/sample_4/topwall.stl type 2 com 1.0 1.0 4.0 ctrlPV force axis 0.0 0.0 1.0 target_val -${f_top} vel_max ${vel} kp ${kp1}

run 500000 # run for confinment

fix_modify twall_servo servo/target_val -${f1_top}

run 10000000
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I have given confinment pressure of 200k. And I have observed that after fix_modify, when next run command is executed. The wall pressure decrease all of a sudden and then again come back to 200k (figure attached).

I want to avoid this. Can anybody help me in this

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Image icon figure_1.png32.21 KB

Forums:

driley | Fri, 02/14/2020 - 00:05

I am having a similar issue when switching between a rate controlled wall to servo wall trying to match the force from previous time step. Were you able to find the solution or can anyone advise?

Rahul Kumar | Wed, 02/19/2020 - 07:41

Hi
I am still working on it, and till now I have not found any solution. I will update if I find any solution.

Are you also doing triaxial test. If yes where you able to do any successful simulation for triaxial test.

mschramm | Wed, 02/19/2020 - 19:26

Hello,
Do you get the same drop if you simply have another run command there?

If you have
run 10000
fix_modify ...
run 10000

simply comment out the fix_modify
run 10000
# fix_modify ...
run 10000

I'm wondering if something is happening in-between the run commands

tjleps | Tue, 03/03/2020 - 11:31

It may also be instructive to run a few time steps without integrating the particle positions when you reset the servo wall so the wall can resettle it's control law before the particles are allowed to move. That way you can deconvolve perturbation from the wall control law vs from particle behavior.

southeast1012 | Sun, 03/22/2020 - 07:47

Hi
I think you can use the run..every command like
run 100000 every 100
fix_modify..
the target value is changed every 100 timesteps.