stress-free packing

Hi Sergei,

for something already implemented, I think you can have a look at randomDensePack
https://yade-dem.org/doc/yade.pack.html?highlight=randomdensepack#yade.pack.randomDensePack

I think there are many methods which have been published, both static and dynamic ones, to achieve what you require. If you decide to go for a dynamic method, I guess the limit is that you will not be able to perfectly reach a stress free condition. If you need a particular PSD, you could do everything in a py script directly, where you would generate the sample you want, load it until your goal porosity and then unload it until you reach very low stress level.

Note that some researchers use interparticle adhesion properties in order to relax the system and get some stress free condition before the actual tests start. It pretty much depends on your needs, but I hope this helps a bit.

Chiara

I better clarify what I said. If, after having reached your goal porosity,
you unload your sample, then obviously you also change porosity itself. I am
not sure how much though. Maybe someone else can comment on this? Am curios
myself.

Cheers.
Chiara

On 16 April 2011 16:31, Chiara Modenese <
<email address hidden>> wrote:

> Question #153042 on Yade changed:
> https://answers.launchpad.net/yade/+question/153042
>
> Status: Open => Answered
>
> Chiara Modenese proposed the following answer:
> Hi Sergei,
>
> for something already implemented, I think you can have a look at
> randomDensePack
>
> https://yade-dem.org/doc/yade.pack.html?highlight=randomdensepack#yade.pack.randomDensePack
>
> I think there are many methods which have been published, both static
> and dynamic ones, to achieve what you require. If you decide to go for a
> dynamic method, I guess the limit is that you will not be able to
> perfectly reach a stress free condition. If you need a particular PSD,
> you could do everything in a py script directly, where you would
> generate the sample you want, load it until your goal porosity and then
> unload it until you reach very low stress level.
>
> Note that some researchers use interparticle adhesion properties in
> order to relax the system and get some stress free condition before the
> actual tests start. It pretty much depends on your needs, but I hope
> this helps a bit.
>
> Chiara
>
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Two ways:
1- Use a geometric algorithm (e.g. K. Bagi papers) , but then the
stability of the obtained packing is not guaranteed and controlling
porosity is more difficult (especially if you fix PSD).
2- Use stress controller, and when you get the correct porosity, unload
it to a near-zero stress, as proposed by Chiara. This packing will be
mechanically stable.

For controlling porosity, you basically maintain a constant stress and
decrease friction progressively:
while (porosity>target):
    friction=friction*0.99
    cycle(1000)

I recommend method 2 unless you really need a 0-stress packing exactly.
But why would you need that if you can always get a a stress negligeable
vs. futur applied load with method 2?

Bruno

Ok, seems, it is clear to me now. Thanks, guys!

>If, after having reached your goal porosity,
>you unload your sample, then obviously you also change porosity itself.

You only recover some elastic deformation. It's small and reversible, and it doesn't really change the particles arrangement. Shear strength, for instance depends on a porosity that can be defined independently of this elastic fluctuations.

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