what is the difference between TriaxialTest (aperiodic) and PeriIsoCompressor (periodic)

Asked by Liqing Jiao on 2011-03-29

Dear all,

Thank Bruno for his reply!

Through tried these different packing, I can see the difference between them. For non-periodic version, we assume six plates to compress particles and decompress them while the radius of particle is given. But for periodic version, no plates occur, and some wire particles occur to envelop the surface of the model while the number of particle is given. If I want to obtain the ball as much as possible, which version may be better? I found that sometimes the periodic version can’t satisfy the requirement. Actually, in some cases, I can see the obvious relative big space between balls. On the other hand, using non-periodic version gets no balls and shows the errors. Sometimes, balls run away or the plates move away from the balls. Thus, I don’t only have no idea about the difference between these versions, but the satisfied model (such as the ball as much as possible in my modeling) can’t also be established. If you still don’t understand my question, please don’t hesitate to let me know.

Look forward to your reply!


Hi Liqing,

Could you please ask questions via : launchpad questions:

The difference is that the non-periodic version will generate spheres
strictly inside a volume, while periodic conditions can give spheres
crossing the edges of the periodic cell.
I must say I don't completely understand your question.


On 28/03/11 05:12, Liqing Jiao wrote:
> Dear All,
> According to the interpretation about RandomDensePack, the explanation
> in Manuals is described like this "yade.pack.randomDensePack(predicate,
> radius, material=-1, dim=None, cropLayers=0, rRelFuzz=0.0,
> spheresInCell=0, memoizeDb=None, useOBB=True, memoDbg=False,
> color=None)[source]
> Generator of random dense packing with given geometry properties,
> using TriaxialTest (aperiodic) or PeriIsoCompressor (periodic). The
> periodicity depens on whether the spheresInCell parameter is given."
> Even through connected with the codes in pack, I can't understand the
> difference between them yet. Besides taking time, what is other
> difference in terms of the physical means or the number of the
> particles? May I get some help from you? Thank you!
> Cheers
> Liqing

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Which version is better depends on what you will do with the packing, mostly. Usually, the periodic version will only be usefull if the generated packing will be used in simulations of periodic boundary conditions (else you get a packing that doesn't fit in the boundaries of your problem).

For number of spheres and error in non-periodic version, I can't help much (I have no experience with RandomDensePack). It seems this function is running a list of relatively complex things all in one. Maybe something has been broken by changes in some engines. If you have a reproducible failure in non-periodic mode, you could open a bug (https://bugs.launchpad.net/yade/+filebug) telling what version you use, what command you type, etc.

If RandomDensePack doesn't work and if you want to better control the number of particles, I suggest using a combination of the makeCloud() function and triaxial controllers, instead of RandomDensePack. See example scripts psd.py (where you can impose the number of spheres in both periodic and non-periodic), triax-basic.py (non-periodic) , periodic-triax-Hzise.py (periodic with arbitrary shape).

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