How to realise force-chain.

Submitted by tshan on Tue, 11/30/2010 - 12:48

Dear all,

I have already done some triaxial tests and simple shear tests, but I want to know the contact normal among the particles and then realise them in paraview to further generate the force-chain.

Is there someone who has done the force-chain stuff before? Could you tell me how to do this or give me some hints?

Thanks in advance!

Best,
Tong

Forums:

JF's picture

JF | Tue, 11/30/2010 - 14:57

Hi Tong,

In fact, LIGGGHTS needs to dump a specific file to display the force-chain in Paraview. You can see this specific file on the forum (see discussion: Dump the connectivity list).

Let me know if you need more explanations about that.

Regards
JF

PS: Have you done these tests with LIGGGHTS ? Have you implemented the triaxial test in LIGGGHTS ?

ckloss's picture

ckloss | Tue, 11/30/2010 - 15:29

Hi all,

you can use the dump local command in conjunction with compute pair/gran/local command in the 1.2 beta
To get this to paraview, somebody would need to write a conversion of this dump local to vtk (eg extend pizza.py)

Christoph

tshan | Wed, 12/15/2010 - 16:01

Hi, Christoph

Could you please tell me how to use the compute pair/gran/local and the dump local command to output pair forces in detail? I do not know how to use them. Actually, after dump the pair forces, it will be possible for me to extend the pizza.py to realize them in Paraview.

Thank you.

Best,
Tong

ckloss's picture

ckloss | Sat, 12/18/2010 - 16:37

Hi Tong, please have a look at the doc for compute pair/gran/local:

compute pair/gran/local command

Syntax:

compute ID group-ID pair/local

ID, group-ID are documented in compute command
pair/gran/local = style name of this compute command
zero or more keywords may be appended

keyword =

pos = positions of particles in contact (6 values)
id = Ids of particles in contact (2 values)
force = contact force (3 values)
torque = torque divided by particle diameter (3 values)
history = contact history (# depends on pair style, e.g. 3 shear history values)

So you can output positions of the two particles, particle ids, components of contact force, and history values

if you use the standard form of the command

compute 2 all pair/gran/local

all these values are output by defaut

schteppe | Thu, 03/10/2011 - 11:09

I'm trying to dump the values from this compute thing to file but I'm having problems. I run:

compute fcompute all pair/gran/local
...
dump forcedump all local 200 dump.force c_fcompute

and get this error:

"ERROR: Dump local compute does not calculate local vector"

I'm not very familiar with this command (yet), and there is no example on the dump local command (maybe you can add this?). What am I doing wrong?

JF's picture

JF | Thu, 03/10/2011 - 11:44

Hi,

If you want to save the position vector, you have to do:

compute fcompute all pair/gran/local pos # don't forget to write what you want to save (e.g. position in this case)

dump forcedump all local 200 dump.force c_fcompute # to dump the three coordinates
or
dump forcedump all local 200 dump.force c_fcompute[1] # to dump only the x coordinate

I think that it is correct, I am not sure. Let me know if it works.

Regards
JF

schteppe | Thu, 03/10/2011 - 13:24

Thanks for the quick answer. I tried to copy-paste your commands and I got some strange results.

dump forcedump all local 200 dump.force c_fcompute # ERROR: Dump local compute does not calculate local vector
dump forcedump all local 200 dump.force c_fcompute[1] # (No error)

Since the latter works, I can extract everything I need for the moment, but the first command should also work, shouldn't it?

Anyway, thanks! I will now continue playing with force chains :)

ckloss's picture

ckloss | Wed, 03/16/2011 - 12:49

No, these two are not equivalent. See the output section of the manual for details.

Christoph

tshan | Wed, 12/01/2010 - 04:19

Yes, I have done the a undrained triaxial compression test and a simple shear test by using liggghts, and it takes me a long time to adjust the parameters. The results such as the q-p figure is resonable but not that good, so I should adjust the parameter such as the consolidation and the compression velocity further to get a better result.

I want to do some micro-analysis further, e.g. the force-chain and the anisotropy.

prasantud | Tue, 05/24/2011 - 19:22

Hi tshan,
I want to do force chain analysis in LIGGGHTS. I have installed it on fedora recently.
could you please give me some suggestion of how to do it.
Best wishes,
prasant

schteppe | Thu, 03/10/2011 - 09:59

I'm also interested in the solution for this.
I found the command "compute pair/local" interesting. Together with the dump local command, one should (according to the documentation) be able to extract pairwise forces from a simulation. It does not seem to work with any of the granular pair styles though.

EDIT: Oops, I didn't see the rest of this thread before posting. Sorry!