# yade-users team mailing list archive

## Re: R: Re: I: Re: Porosity

```Hi Chiara,

```
If you have a moment, you could extract the main points of this discussion and put them in the F.A.Q section of Triax documentation, it is relevant.
```

Cheers.

Bruno

Chiara Modenese a écrit :
```
```Thanks Bruno, now I understand.

Chiara

```
```----Messaggio originale----
```
Da:
```bruno.chareyre@xxxxxxxxxxx
```
```Data: 20/01/2010 9.47
```
```launchpad.net>
```
```Ogg: Re: [Yade-users] I: Re:  Porosity

```
Question: which
value of friction angle do you use during the
compaction phase? Should be
the final one or should be lower than
that? Would it be possible to run the
analysis with a value equal to
```zero?
```
Anything between 0 and the
final value. Higher than the final value
would result in volumetric collapse
```at the beginning of the test.
```
I would expect that also at a small level
of stress on the walls,
```this value of unbalanced force remains quite low.
```
```
```
unbF is non-dimensional, it is not affected by the level of stress. See it
```as a percentage of the loading.
```
I suppose that the reason you (if it were
you) put the bool
isARadiusControlIteration relays in the concept of
maintaining a
quasi-static equilibrium as much as possible during the
analysis.
```I see the problem now.
```
The point of cycling without expanding is
just to speed up the
simulation. Increasing sizes need an iteration on all
bodies, and one on
interactions. It is expensive. Increasing by 1e-5 at each
step is more
```or less like increasing by 1e-4 each 10 steps, so...

```
```
```
Actually, unbF _should _be close to 1 during the begining of the growth,
```
```
since most particles have 0 (unbF undefined) or 1 contact (unbF=1, since the
resultant force IS the contact force in this situation). The only
time when
you really want it low is at the end of the compaction. I
don't really care
if the compaction is dynamic in between, and for sure
the interval between
growth is too small to let the sample really
```stabilize.
```
To make a summary
I see that the unbalanced force reaches low values
(say 0.07 or whatever)
only after having compressed the packing. Am I
```escaping something?

```
```
```
That is correct and expected. Gaz particles can't be at static equilibrium
```under pressure, dense packings with many contacts can.
```
```Cheers.

Bruno

```
```
```
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_______________________________________________

```
```

--
_______________
Bruno Chareyre
Associate Professor
Grenoble INP
Lab. 3SR
BP 53 - 38041, Grenoble cedex 9 - France
Tél : 33 4 56 52 86 21
Fax : 33 4 76 82 70 43
________________

```