LIGGGHTS® - User Forum

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

Hi

I want to read in values from a text file so that I can control the speed of a rotational boundary condition that I have created (similar to conveyor - covered in another post). I want to read in two columns of numbers and assign each one to an array. This way I can calculate the speed based on the solution time. What would be the best (i.e. simplest and efficient) way of doing it?

Hello.
Is there a refs. where rayleigh_time and hertz_time expressions are derived?

And more, I see an error in the check/timestep/gran documentation.
In the doc:
dt_r =PI*r*sqrt(rho/Y)/(0.1631*n+0.8766),
But in code instead Y used shear_mod.

Also, for dt_h. In doc:
dt_h =2.87*(m_eff²/(r_eff*G_eff²*v_max)^0.2.
But in code instead G_eff used E_eff.

Hello.
What is mean of the frictionflag in wall/gran style?
I thought if the frictionflag is zero then the wall without friction. But the test showed that it is not.
In test script a sphere moves along yplane with given initial velocity. If yplane is frictionless then sphere's velocity should not be changed. But it is changing, see attached figs. And in different ways depending on the value of the flag.

And if I need frictional and frictionless walls should I to define 2 atomtype?
Thanks.

Test script:

#Particle packing by insertion and successive growing of particles

Hi,

I reinstalled my ubuntu distribution. I installed LIGGGHTS and everything worked properly (it compiled and created lmp_fedora). But when I want to execute lmp_fedora my terminal is reporting:

fuchsjosef@ubuntu:/media/Volume/LAMMPS/liggghts_1p2p9/src$ lmp_fedora
lmp_fedora: command not found

Maybe someone can help me
Josef

Hi,
I'd like to use different friction for different stl.
For example I'd like to set friction on stl 1 grater than stl 2.
I tried something like:
fix cad1 all mesh/gran/stressanalysis stl1.stl 1 0.001 0. 0. 0. 0. 0. 0.
fix cad2 all mesh/gran/stressanalysis stl2.stl 2 0.001 0. 0. 0. 0. 0. 0.
But it request me 2 atom types.
Have I to set 2 atom types?
If yes, how have I to set the friction between the 2 types: fix fr all property/global coefficientFriction peratomtypepair 2 value_11 value_12 value_21 value_22 ?