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["Danny (Dingeman) van der Haven" <question699428@xxxxxxxxxxxxxxxxxxxxx>]

Question #699428 on Yade changed:
https://answers.launchpad.net/yade/+question/699428

    Status: Answered => Solved

Danny (Dingeman) van der Haven confirmed that the question is solved:
Dear Jan,

> depends on what "essential" is.
> Also depends on what "some sort" is, because periodic boundary conditions essentially are "some > sort of wall"..

A wall that interacts with the particles like a physical wall is
necessary for me to be able to make the comparison I mentioned in the
original question.

> What is the reason of stress variation? Dynamics? Gravity? Something else?
> For "fast" loading yes, the stress waves should not be neglected and "wall" loading is more realistic.
> Contrary, for "slow" loading, this "periodic approach" is actually more realistic than the loading 
> induced only by planes (which induce stress waves not present in reality).

These are valid concerns / questions. This is why I want to do the
comparison between plate compression and periodic compression. I study
the compaction of pharmaceutical powders. The speed of the compression
can be 0.1 mm/s (quasi-static) but also 950.00 mm/s (dynamic) for
tablets with a final thickness of 4.00 mm. Gravity is not a concern, but
dynamics and wall interactions are. For slow compression speeds the
variation in stress along the compression axis is likely caused by
interaction with the side walls. The comparison is mainly to look at the
potential differences made by dynamics.

> is it still freezing, or just the behavior and results are not as
expected?

The simulation iterates, but the behaviour is not what I was aiming for.
The box stays the same size so the wall do not exert any pressure on the
particles. The cell does change.

> If you set homoDeform=0, you should not get the "scaling"

Thank you, that option indeed disabled the scaling / shifting of
particle coordinates.

> b.state.blockedDOFs = "xyzXYZ”
> b.state.vel = someConstantVel

This solved my problem! Thank you! I created a periodic box with an
extra long z-axis. Using two box-plates I can then compress the
particles in the z-direction using the blockedDOFs and vel options,
keeping periodicity in the x and y directions.

> basically yes, you can compute stress assuming static equilibrium or
you can somehow take into account inertia of the particles.

So that means if dynCell = False you assume static equilibrium and if
dynCell = True you take into account the inertia?

> yes, it seems like a bug

I filed an issue report on Gitlab.


Kind regards,
Danny

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