wiggle z not working with fix/wall/gran?

Submitted by ericparteli on Thu, 07/12/2012 - 11:57

Dear developers and users of LIGGGHTS,

I can't set z-plane walls to wiggle in LIGGGHTS using fix/wall/gran.
When I use walls from a CAD file (mesh/gran) then wiggle works fine.

Please see the attached in.packing_wiggle file, which is nothing but the in.packing file from the EXAMPLES of LIGGGHTS with some small modifications, i.e. I just added gravity in z direction, changed the position of the z walls and made them wiggle by an amplitude of 1. And although it should cause an oscillation with a huge amplitude - if I did everything correctly - I don't see (?) the expected change due to the wiggle.

Am I doing something wrong in the in.file? Or maybe there is really a bug with the wiggle function (which I consider as improbable)?

Thanks so much in advance for any hints to solve this problem!
Eric
P.S. Oh, and the wiggle of LAMMPS also works fine here :) The problem I am encountering refers only to using wiggle in LIGGGHTS.

AttachmentSize
Plain text icon in.packing_wiggle.txt2.8 KB

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ericparteli | Thu, 07/12/2012 - 14:29

Hi, everybody,
the in.packing_wiggle.txt is correct and is working fine with liggghts_1.5.3.
So obviously I did an error elsewhere and will just check.
Best
Eric

ckloss's picture

ckloss | Thu, 07/12/2012 - 14:43

The wiggle option for primitive walls was removed in 2.X (shear is still possible) but this did not find it's way into the doc and error check
I'll add an error check and update the doc accordingly

Note that you can do wiggle (and much more) with fix move/mesh

Regards,
Christoph

ericparteli | Thu, 07/12/2012 - 15:30

Hi, Christoph,
great to know this, thanks for informing me about the modification in the wiggle in the 2.X version. Oh yes, I always prefer to use move/mesh function too and this is really a great utility! Though the built-in wall functions for simple geometries can be useful for small tests since they are so simple to handle and specially if you don't have drawn your CAD geometry yet :)
Thanks so much for all the enlightening discussions of today about wiggle in LIGGGHTS!
Eric

xavier.tricoche | Tue, 07/17/2012 - 20:03

Hi,

To follow up on this topic:

I am a bit confused as to what group-ID should be provided to a fix/move in the case of a primitive wall defined as zplane. In this case, it would appear that all I have is a fix-ID (associated with the fix that instantiated the wall) but no associated group-ID that this fix would apply to.

I must be missing something and I would greatly appreciate any clarification you can provide.

Thanks.

ckloss's picture

ckloss | Tue, 07/17/2012 - 22:22

Hi xavier,

there is no such thing as a fix/move in the case of a primitive wall defined as zplane. To clarify this:

+ whatever wall you use, the group is used for defining which particles the wall force is applied to
+ if you use a primitive wall, you can apply shear ("shear" keyword), but the wall position is not changed.
+ if you use a mesh wall, you can use fix move/mesh to move it. The group ID is ignored in this case, as stated in the doc

Hope I could help

Cheers, Christoph

xavier.tricoche | Wed, 07/18/2012 - 02:13

Thanks so much for your quick answer. I guess all I need is a trivial 2-triangle plane definition to be handled and wiggled as a mesh.

Thanks again.