LIGGGHTS® - User Forum

Hi.
I have a problem with per-atom stress calculation.
I modify examples/packing script in order to calculate and dump per-atom stresses. So, I add the line:

64: compute st all stress/atom ke pair

and modify the dump command:

68: dump dmp all custom 350 post/dump.packing id type type x y z ix iy iz vx vy vz fx fy fz omegax omegay omegaz radius c_st[1] c_st[2] c_st[3] c_st[4] c_st[5] c_st[6]

But I got a error:

ERROR: Per-atom virial was not tallied on needed timestep

What is this?
I attach modified script

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Upd: The script

Hi all,
Can we define functions in LIGGGHTS script? I mean, define a section of codes that can be used elsewhere in LIGGGHTS script.

Thanks in advance.

Cheers,
Tao

Hi,

I may modify the LIGGGHTS code for a new contact model and do some basic benchmark tests. May anybody tell me how to fix the position and rotation of a particle in a simulation (its force and interaction with other particles remained ), and how to output the damping force of a particle?

Regards
Jerry

Hi,
I'd like to see particles as a kind of "grid" (see the picture I attached).
Do I have to set some group to make this?

Thanks for any help

Andrea

Hey Chris,

There has been a recent paper published in Powder Technology: An investigation of the comparative behaviour of alternative contact force models during elastic collisions (2011) C Thornton, S J Cummins, P W Cleary; which may be of interest for you.

Hi all,
I'm new to LIGGGHTS, and know quite little about the code. Thus, this question may appear to be quite simple for all of you.
In the simulation code, we just use numbers, e.g. 1,2... to represent different types of atom. I just wonder what's the really meaning of atom_types? Is there any relationship between these numbers and real atom_types?

Please give me some ideas about that.

Cheers,
Tao

Hello all !

I tried to define a variable function for youngs modulus , poisson ratio and the 2 coefficients as temperature dependent, but encountered an error telling me the values must be floating point.

Is there any way of defining the materials properties in liggghts as dependent on temperature or timestep for example ?

If so, what's the easiest way of doing so ? (I assume it involves the modification of some code)

Thanks !

Hi Liggghts users,
I'm new to LIGGGHTS. Recently, I tried to import CAD mesh file (stl file) into my model, but resulted in errors.
It always says:
Importing STL file 'simple_chute.stl'
ERROR on proc 0: Cannot open stl file simple_chute.stl

Actually, I put both LIGGGHTS in file and stl file in the same folder. But the same error occurs every time I run the simulation. I do not know what's going on. Can anyone help me about this?
Many thanks!

Yours,
Tao

Hello everybody,

I'd like to create my own simple STL meshes. Until now I did not use a mesh generator.
What is the simplest software to start with? (Gmsh seems a little bit too sophisticated for the beginning)

Thanks
Sebastian

Hello,

I have problems with understanding a few commands:

The simulation issue is a box filled with particles where I want to analyse stress on different heights of the walls.

I use these commands

fix cad all mesh/gran/stressanalysis cube 1 1 0 0 0 0 0 0 finnie yes
fix GlobalforceOnMesh all ave/time 50 2 100 f_cad[1] f_cad[2] f_cad[3] file filename.txt
dumpstress all mash/gran/VTK 200 post/dumpCAD*.vtk stress wear cad