LIGGGHTS® - User Forum

Hi LIGGGHTS users,
Please anybody tell me if granular particles of LIGGGHTS are viscoelastic in nature? I mean we can transfer sound waves in the granular media.
Thanks,
A

Hi,

Does anybody know- is there any way to set the angular velocities of atoms to a specific value?
For velocities I can use fix_move and from a quick check I did I cannot find any similar option in LIGGGHTS as the rotate keyword does something slightly different.

Will I have to extend fix_move?

Thanks,

George

Hi,

I would like to model a viscous drag force (stokes drag) for a polydispersed simulation where the particle size distribution is specified using fix_particletemplate/sphere and fix_particledistribution/discrete. Since, all the particles have similar properties, I would also like to have one atom_type in the simulations.

In case anyone finds it useful here is some information about a method I use to couple Liggghts with a separate Lattice Boltzmann code written in Fortran.

The Fortran code is the driver, so it starts first calculates the fluid flow, writes the particle information to a file and then calls an external subroutine to run Liggghts automatically from the command line for one time step. See the following link.c file:

#include
#include
int dem_(int i)
{
printf ("Checking if processor is available...");
if (system(NULL)) puts ("Ok");
else exit (1);

Hy @ all,
I would like to calculate & print out the mass and the number of particles included in the calculation area.
I ´ve tried to use the following commands:
variable m equal mass(all)
fix extra all print 100 "$t $m" file out.txt screen no title "%step totalmass"

but I don´t know whats really calculated with this command.

It would be nice, if someone could help me,
Michael

Hi,
I got error when I use following commands in script:

compute 2 all stress/atom
fix 10 all ave/spatial 100 5 1000 z lower 0.001 fx fy fz density/mass density/number c_2[I] c_2[2] c_2[3] units box file vel.profile

..
.
.
ERROR: Fix ave/spatial compute does not calculate a per-atom vector
However, Fix ave/spatial takes input as per-atom vector.
Thanks,
Ram

Hi,
I want to simulate a quasi-static compression test for cohesive granular particles. In keeping with the quasi-static assumption I want to apply the total wall displacement in several tiny increments. After each increment the walls should be held in place and the particles should be allowed to reach equilibrium (that is the kinetic energy should go close to zero). Thus each displacement increment is to be followed by kind of a relaxation step. My question is how do I achieve this using liggghts?

Hi,
I want to change the value of a variable after a certain number of timesteps. I tried to do this using the following lines in my script

run 10 pre no post no every 1 &
"variable vke equal step" &
"if ${vke} > 5 then 'variable xp0 equal 1' "

I get an error after the 6th timestep (when the if condition becomes true): ERROR: Unknown command: 'variable

So it seems the nested quotes are a problem. I have also tried changing the quotes to

"if '${vke} > 5' then 'variable xp0 equal 1' "

but in this case the if condition is just completely ignored.

Hi,

Does anybody know if the LIGGGHTS programme can be used in two dimensional conditions? In the source code, somewhere I see it says it is only valid in 3D. How can I do with LIGGGHTS to carry out a 2D biaxial test?

Thanks.

Jerry

ave/spatial problem for obtaining a section averaging

Hallo everyone ,,
im running a simulation on LAMMPS and i need to have a section with averaging values of particles to compare it with other results ,,,so i need to creat a box in the middle of the box and then average the values of the particles within this BOX ,, the problem is that i cant define 3d bin !! i always get error message when i define more than one dimension in fix command !!

dimension 3
boundary p fs p