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[Sarath Chandra Reddy <question697174@xxxxxxxxxxxxxxxxxxxxx>]

Question #697174 on Yade changed:
https://answers.launchpad.net/yade/+question/697174

    Status: Answered => Open

Sarath Chandra Reddy is still having a problem:
Thank you, Dr. Bruno, for the prompt reply and for sharing your knowledge of how the servo engine works. 
The problem is your parameters are extreme and the servo control of boundaries doesn't like that:
Super-high stiffness with super low confinement.
Here, I used higher particle young’s modulus value as in the Mindlin model the stiffness also depends on contact overlap. As I understood previously from PFC 3D that even at E = 100 GPa, the normal stiffness values are in the range of 10^4 – 10^5 N/m after the confinement stage as compared to the Cundall and Stark model (Linear model) where people use normal stiffness in the range of 10^8 N/m. 
If you visualize interaction forces in the 3D view you can see that they keep blinking, that's because the walls struggle to maintain constant stress and the force oscillates between zero and something.
Yes, I also observed this.
The particular case also leads automatic timestep to not be correct (may also be linked to the viscous Mindlin law you are using).
Without changing the physical problem I could stabilize your script with:
timestepSafetyCoefficient=0.25
triax.max_vel=0.002
I will try this
I would also avoid using a super low confinement-to-stiffness ratio (1e-6 in your case) if possible since it makes the whole thing not very efficient.
okay
I'm surprised that randomDensePack seems to not reload previous packs despite you using memoizeDb. Do you see the same behavior?
Yes, I was also surprized to see this behavior. This is one of the reasons, I raised the query as I doubted that I did something wrong with the code.

I would discourage generating a randomDensePack for a triaxial loading since, what it does is actually another triaxial loading. Then when you load it as an initial state you have a discontinuity in mechanical properties which makes it unstable again. Especially in your super-stiff case. Just a waste of computation time.
Better do everything in same conditions.

Are suggesting to use other ways for particle packing generation.
Can you please let me know if you recommend makeCloud with gravity settlement and using the Boundary contraction procedure be used to attain approximately the required porosity works better for this case? Please suggest if any other better way is available.

My study is more focused on the deviator stress vs strain behavior just
after confinement. I wanted a mechanism that can replicate the effect of
particle properties on initial slope of the deviator stress vs strain
curve, i.e., with increase in particle young’s modulus, possion’s ratio,
the slope of deviator stress versus strain should increase.

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