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[Jan Stránský <question701259@xxxxxxxxxxxxxxxxxxxxx>]

Question #701259 on Yade changed:
https://answers.launchpad.net/yade/+question/701259

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hello,

> I am ... a new member of this forum.
> I just started using YADE and more generally DEM

welcome :-)

> I am supposed to generate an isotropic pressure which should not
change the void ratio of the cell.

it depends on definition of void ratio or definition of values from which it is computed.
If you apply pressure / velocity gradient, the total volume of the cell is changing, so intuitively also void ratio would change.

> I computed void ratio = 0.91

how?
A MWE (see below) would help

> 1) therefore, is it correct to affirm that I could have a regular
packing with any isotropic pressure I decided ?

yes, you can have a regular packing with any (reasonable) isotropic pressure.
Reasonable = e.g. with linear contact law (e.g. Law2_ScGeom_FrictPhys_CundallStrack) the pressure is limited by stiffness (with higher pressures resulting in degenerated collapsed "one-sphere" packing)

> 2) then, after reaching the target isotropic pressure,, I tried to
apply an ideal shearing by
O.cell.velGrad=Matrix3(0,rate,rate,rate,0,rate,rate,rate,0), imaging
that this deviatoric component will produce compaction without changing
the isotropic component. But I obtained the opposite effect, the void
ratio did not change, whilst the mean pressure did increase. Why so?

ideal shearing ... compaction ... isn't it contradicting?
Void ratio does not change, because total volume does not change (because of ideal shearing).
To help you why the pressure increased, we would need a MWE (see below).

> 3) if so, I would like to obtain the desired void ratio at a given
isotropic pressure without changing the particle radius. What is the
best approach?

Depending on definition, but I feel like one of the values is dependent on the other.
I.e. you cannot independently vary pressure and void ratio.

Cheers
Jan

PS: also please read [1] and consider point 5 and consider providing a
MWE.

[1] https://www.yade-dem.org/wiki/Howtoask

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