yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

Hi,
> I would need your help concerning the Triaxial. Since I need a 
> specific value of final porosity, I am trying to do something in your code but 
> without success (BTW, I DON'T want to modify your code, if it will work I will 
> manage to add a flag or something like that).
>   
No problem. Just keep me updated so I know what happens in files.
> so basically in the line 
> (1) it is like saying "cycle" without expanding if the value of Unb force is 
> too high. Unfortunately "cycling" doesn't help (why? Should it?), the computed 
> unbalanced force is always very high and around 1.
>   
There is nothing "bad" in keeping a constant radius until unbF is small.
If the unbalanced force does not approach 0 with cycles "_supposed to 
be_" doing nothing else than dynamic integration, there is clearly 
something wrong. The timestep is not 0?

The only problem I see in your approach is you force the porosity you 
want, which will result in very big overlaps and high stress most 
likely. The porosity should be the result of a "realistic" packing 
evolution.

> Could you give me any 
> suggestions or directions how to do that? I mean, how to fix the value of final 
> porosity..
>   
Keep a constant stress and decrease friction a little bit at each step. 
The packing will self-reorganize, and porosity will decrease. Save the 
packing state when porosity value cross the value you want.
You can use this function to modify friction :

void TriaxialCompressionEngine::setContactProperties(Scene * ncb, Real 
frictionDegree)//I really mean "use", not copy ;)

All you have to do is a loop that will keep assigning frictionDegree 
each n=~10 steps, with a decreased frictionDegree each time.
Note that big porosity variations usually occur with small values of  
friction, in the range 0° < f < 5°.

> I have got that having a specific PSD and a 
> friction angle we can get only one possible value of final porosity (or a very 
> small range of it) and that's true with the DEM (cause we are dealing with 
> spheres and not irregular shapes) but to me it is always possible to say that 
> for the same PSD I would like to run the Triaxial with an higher porosity 
> (higher than that maximum dense packing I get with this method either with 
> compaction or expansion).
>
>   
What is small range? I tried that after your message and I got different 
poro from different friction.

> Merci beaucoup.
>
>   
Prego.

Bruno