Are there any command or code available to control the force or pressure on a wall?

Submitted by jerry_1988 on Wed, 10/05/2011 - 15:47

Hi my friends,

I want to compress a packing by a specified force or pressure. Are there any command or code available now to control the force or pressure on a wall? Do I need write some extra code on LIGGGHTS to reach my purpose?

Thanks.

Jerry

Forums:

ckloss's picture

ckloss | Wed, 10/05/2011 - 19:07

currently not directly. you would either have to modify the code or do this on the scripting level by accessing the force that the particles extert on a wall (fix mesh/gran/stressanalysis). See also discussion here: node/547

Christoph

dbreton's picture

dbreton | Wed, 10/05/2011 - 21:44

I have been thinking about this as well (and have reviewed the earlier forum postings), since I need to perform constant stress compaction.

Here are my ideas:
1. Build a special group of "piston" particles, and then apply the avgforce fix to them (see LAMMPS/LIGGGHTS documentation). This fix is supposed to prevent deformation of the group, so presumably we get a non-deforming piston exerting a constant force on the material below it.

2. Similar to the idea above, except that the group of piston particles are (a) very dense, to apply the correct pressure due to gravity and (b) rigidly bonded so that the piston does not deform.

I agree that these are less than ideal (especially if pressure distribution on the piston is desired) solutions but may at least be a simple "hack" to get started on the problem.

I'll let you know how (or if) this works, hopefully by the end of the week.

regards,
DAN

jerry_1988 | Thu, 10/06/2011 - 12:05

Hi DAN,
constant stress testing

Your idea should be a possible way to do some simple compression test. I will think about that, thanks.

Somnath | Tue, 03/06/2012 - 23:08

Hi,

Has anyone worked further on 'applying constant stress on a wall' feature by modifying the stressanalysis fix along with the move/mesh fix?

I would be very interested to know about it or if anyone has a code they can share. Also, I think it would be a valuable feature in LIGGGHTS if a constant stress can be maintained on a wall directly.

Thanks
Som