yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

chiara.modenese@xxxxxxxxx a écrit :
> Hello,
>
> quick question on one aspect of the Triaxial Test. As a beginner, I am 
> just trying to run some triaxial tests but I have got this error message:
>
>
> Exceeded 3000 tries to insert non-overlapping sphere to packing. Only 1055 
> spheres was added, although you requested 2000
>   
The initial positioning of spheres is done by generating random (x,y,z) 
and checking if a sphere of radius R (R also randomly generated with 
respect to a uniform distribution between mean-std_dev and mean+std_dev) 
can be inserted at this location without overlaping with others.

If it the sphere overlaps, you generate new (x,y,z)'s until you find a 
suitable place for the new sphere (*). This explains the message you 
have : after 3000 trial-and-error, the sphere couldn't be placed, so the 
algorithm stops.

I guess you tried to generate a dense packing, which is not possible 
with this method. You should keep the default value of porosity.
The dense state will be obtained in the second step (compaction, see below).

> BTW, could you 
> also explain me the meaningful of the following variables, since I was unable 
> to find where actually they are employed in the code.
> maxMultiplier,
>
> finalMaxMultiplier,
> maxWallVelocity.
>
>   
Compaction is done (1) by moving rigid boxes or (2) by increasing the 
sizes of the particles. Both algorithm needs numerical parameters to 
prevent instabilities. For instance, with method (1) maxWallVelocity is 
the maximum wall velocity, with method (2) finalMaxMultiplier is the max 
value of the multiplier applied on sizes.


(*) I just realized there is a bias in radii generation. If the sphere 
does not fit at (x,y,z), a new R is generated. Which means small R tend 
to be a bit more frequent that big R, even though the distribution is 
supposed to be uniform between Rmin and Rmax. I'll commit a fix in a few 
minutes.

Bruno
>   


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