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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,

thanks for more info.

> But this has been removed from the MWE below because it is not
interesting now.

+1 for understanding the meaning of MWE (which is not a matter of course
at all)

> Briefly, I am reaching my target pressure by
O.cell.velGrad=Matrix3(-rate,0,0,0,-rate,0,0,0,-rate) which cannot
change the void ratio of a regular ortho packing.

But isotropic pressure (applied as constant isotropic velGrad) DOES change the void ratio (because it changes total volume).
Just see the output of the script (where "e" is decreasing).
Am I missing something?

> So, I am just now pushing one wall by
O.cell.velGrad=Matrix3(-rate,0,0,0,0,0,0,0,0), reaching the target void
ratio.

Why not 3 walls? (related to above (?))

> 1) modify the elasticity of the material

yes, introducing another variable, you can now vary pressure AND void
ratio independently and stiffness is now the dependent variable.

> O.materials[0].young =En*factor

be aware that modifying material has no effect on existing interactions
(only on the newly created)

> 2) modify the branch vector ...
> ...
> I tested 1)
> ...
> What do you think about this approach?

I like 1) more.
One reason is that I have almost no experience with 2 :-) 
But more importantly I **think** like the two approaches are very similar - modifying material to introduce another variable to let void ratio and pressure be independent.

> I can see the drawback is the change of the contact stiffness and
indeed I would like to explore the approach 2) to avoid that.

Yes, there are drawbacks. E.g. that you define material to get good result, but usually the material properties (stiffness is usually the most basic) are the inputs.
What exactly is meant by you?

Cheers
Jan

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