Exclude interaction of frictional wall with selected particles

Submitted by tapsab on Fri, 08/10/2012 - 18:34

Hi,
Is there a way to turn off the interaction between a frictional wall (imported using "fix mesh/surface") and a selected group of atoms in a simulation? I want the wall to act as boundary only for some atoms in the simulation and not for others based on the atom type. I tried using the "neigh_modify exclude" command but it does not seem to work for walls.

Any suggestions would be appreciated.

Thanks,
Tapan

AttachmentSize
Plain text icon Input.txt2.06 KB
Plain text icon Stl.txt521 bytes

Forums:

cstoltz | Fri, 08/10/2012 - 20:43

Never tried that myself, but I think you just need to define your groups of particles properly, and then define the fix_wall_gran command so that the the wall group only refers to those particles you want. For example, the line might read as follows:

fix wall group1 wall/gran/hertz/history mesh n_meshes 1 meshes cad1

where 'group1' is the group name for those particles that should interact with the wall and 'cad1' is the name of your fix importing the mesh.

Please post to let me know if this works.

Chris

tapsab | Fri, 08/10/2012 - 21:50

Chris,
Thanks for responding. I tried the solution of specifying a group-id in with the "fix wall...." command but it just ignores the group-id. I have attached a simple script with two particles falling on a flat surface under gravity in my original post if you want to look at it. I wanted to see if I can make just one of the two particles interact with the bottom. The bottom mesh is just two triangles and is stored in the Stl.txt file (also attached) please change the name to Bottom.stl if you want to run it.

cstoltz | Mon, 08/13/2012 - 12:32

That's interesting - I tried playing around with it a bit as well, using different pair_styles and different ways of specifying the groups, but with no luck either. It seems to work fine in version 1.5.3.

Christoph - did something change regarding the group specification in the fix_wall_gran statement?

Regards,
Chris

ckloss's picture

ckloss | Mon, 08/20/2012 - 23:05

Hi Chris and Tapan,

you're right - taking care of the fix group is missing in LIGGGHTS 2.X - will fix that in the next release.

Thanks, Christoph

Zheng Hu | Thu, 11/02/2017 - 18:10

Dear Christoph,

I am classify two particles by defining two different groups, while I met the similar problem as this post. You can see that I set the interaction only between the bparticle group and the wall. However, the sparticle group also has interaction with the wall as the result shows. Is there still a bug in the latest version LIGGGHTS 3.7? Do you know how to solve this problem?

I have also post this question in https://www.cfdem.com/forums/how-set-one-type-particles-goes-through-mes... .

Attached please find the code I use to separate these two particles:
#groups of atoms: big and small particles
group bparticle type 2
group sparticle type 1

#distributions for insertion
fix pts1 all particletemplate/sphere 15485863 atom_type 1 density constant 2000 radius constant 0.001
fix pts2 all particletemplate/sphere 15485867 atom_type 2 density constant 2000 radius constant 0.002
fix pdd1 all particledistribution/discrete 32452843 2 pts1 0.2 pts2 0.8

fix wall bparticle wall/gran model hertz tangential history mesh n_meshes 2 meshes topwall bottomwall