LIGGGHTS® - User Forum

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

Hi,
Is it possible to dump snapshots in a format which can be read by EnSight? Or, is there a way to convert them into ensight format by pizza?
Any clue will be appreciated.
Thanks
Ram

Hi, all

Is it possible (or simply naive) to run the MD and DEM simultaneously in one model? I am wondering if it is feasible to use a cluster of atoms to assemble a nano granular particle which can contact with other particles? The interaction between the atoms within one particle is governed by MD potential function (e.g. Lennard Jones) while the contact between particles follows the contact law (e.g. Hertz).

Any suggestion and discussion is appreciated.

cheers

Yang

Hi!
Has anybody got LIGGGHTS working under Sun Grid Engine with $round_robin -scheme? I've only managed to get it work with $fill_up and even then every calculating node for the simulation has been on the same computer. I'm using OpenMPI-1.5.3 and it has been compiled --with-sge (haven't seen any difference, if this flag has been used or not...). Without SGE it works perfectly fine. Some simple hostname calling scripts under SGE with mpirun works also fine.

- Timo

Hi, all

How to choose an appropriate timestep in LIGGGHTS? In the examples, I presume the timestep, e.g. 0.00001, is not generally applicable.

Normally a ratio of the out-of-balance force over the average contact force is used to assess if the granular system is stable or not. I'm just wondering whether this is robust in LIGGGHTS or I have to take care of the timestep by myself in each simulation?

cheers