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Re: About SDEC packing


yuannian wang a écrit :

*/Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>/* wrote:

    1/ Random generation in a box (without contact - without gravity).
    2/ Radii expansion until one prescibed value of the confining
    is reached
    3/ Possibly : decreasing slowly the contact friction to densify
    the packing.

    The packings obtained are homogeneous and isotropic, and you can
    the final porosity and the relative particle size distribution.
    It is the only method I know that combine all those aspects.


Hi, Bruno:
    Thanks for your information!  Seems good. I guess your method is a
    dynamic way for packing.(?)

You are right, it is dynamic.

     Generally dynamic approach will cost more time than purely
    geometric way. How long will it run a packing, like saying, for
    10,000 spheres in 2D?  Also for 3D problem, the computation
    consumption will increase dramatically.

Yes, it costs more time. But geometric ways of packing have drawbacks that can be real issues or not, depending on what you want to simulate : the compacity can't be user-defined, some methods don't give isotropic packings, etc... Packing for 10000 spheres in 2D : about 1,5h. In 3D : about 3h (the increase in time between 2D/3D is not so dramatic). Simulation of a compression test on the generated sample is about 2 or 3 times more, and you can perform many tests on one sample. So yes it costs, but it is not the major cost in most simulations. I agree however that it could be good to have one quick geometric method when one does not want to wait.
Personnaly, I will need a dynamic method.

    We may have to consider this. Can you share your 2D packing code
    to me? Let's see if I can modify it into 3D. If it works I'll back
    the 3D code to you guys.

I could share my 2D code without problem but it is written in Fish langage (langage of PFC, the commercial DEM code from Itasca). I think it would be useless for you.
Today, I will try to write the algorithm and send it to you.
We need :
- a random number generator
- a dynamic engine (Yade will do the job ;))
- the code for simulating rigid walls and for measuring the pressure on the walls (I have already written this for Yade and I can send it to you) - the code for increasing/decreasing the size of particles depending on the measured pressure (not done)
- the code for decreasing contact friction.(not done)
- the code for computing compacity (I can do it very quikly).

I will also send you the code I have already written in Yade for triaxial tests, it is not in the current release of Yade. In the triaxial test, there is already one box with grains floating inside (with positions from the text file small.sdec.xyz if I remember well...) and walls applying confining pressure.

Bruno Chareyre

Chareyre Bruno
Maître de conférence

Institut National Polytechnique de Grenoble
Laboratoire 3S (Soils Solids Structures) - bureau I08
BP 53 - 38041, Grenoble cedex 9 - France Tél :

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