"particle wall" created by using "fix rigid"

Submitted by adabubu on Wed, 06/29/2011 - 15:20

Hi,
I created a "particle wall" by using "fix rigid" and tried to let this "particle wall" to compress the particles filled in a cylinder under gravity (so there are totally three materials: filled particles, "particle wall", cylinder wall), but i got very strange result. The "particle wall" pass through the filled particles and even the cylinder (if the timestep is many enough). It appeared that this "particle wall" didn't compress the particles filled in the cylinder at all. Does anyone have any idea about this problem?

Thanks
Xuetao

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ckloss's picture

ckloss | Wed, 06/29/2011 - 15:47

Hm, remote diagnostigs is difficult (if not impossible) in this case.
Anyway, you should ensure that the cylinder wall does not apply to the particles in the rigid group. Also, you should add a neigh_modify exclude group rigid rigid.

A way without fix rigid would be to use fix freeze / fix move for the same task.

Christoph

adabubu | Wed, 06/29/2011 - 16:16

Yes, i nocite that. Well, basically what i tried is based on the discussion "how to induce stress-control compression test" in the forum. Tong had given the following advices:

If you really want to this currently, from my perspective, it may be possible to set a "particle wall", which the "wall" is actually particles:
1)use lattice and create atom command to creat a dense particle wall (make sure it is dense enough, or the inner articles will explode);
2)bond them together (fix rigid?) and then induce gravity to the particle wall group;
3)let the particle wall to compress the inner particles.

In order to make sure about the rigid body, i have done a simple simulation which "partilce wall" fell down to an empty cylinder by gravity. There is no problem in this simulation, the "particle wall" fell into the cylinder. But if the cylinder is not empty, the "particle wall" just go through the filled particles and even the cylinder bottom.

By the way, i used the command "neigh_modify exclude", but still i got same strange result.

Would "atom_style hybrid" help? If it would, which atom style besides granular should i use?
Thanks
Xuetao

ckloss's picture

ckloss | Mon, 07/04/2011 - 12:39

these 3 steps are logical

>>There is no problem in this simulation, the "particle wall" fell into the cylinder.
>>But if the cylinder is not empty, the "particle wall" just go through the filled particles and even the cylinder bottom.
If you send me the script I can have a look, but it will take some time

>>Would "atom_style hybrid
no, that's something completely different.