LIGGGHTS® - User Forum

Hi all!

I was looking into literature to find out more about coarse-graining in granular simulations. I have found the paper "Three-dimensional discrete element models for the granular statics and dynamics of powders in cavity filling - C. Bierwisch Ã, T. Kraft, H. Riedel, M. Moseler (2009)" where the dimensional analysis is explained.

My question is: do I have to adjust the material properties used by the gran model hertz (Youngs modulus, Poisson ratio, coeff of restitution, coeff of friction) if I scale the particles by a certain factor?

In the newly released LIGGGHTS,serial multisphere method is included.

Hi all,

Could you please tell me how can I use hybrid mpi/openmp parallelization in LIGGGHTS ?

thanks in advance,

Reza,

Greetings,

I've been having the same error for some time when meshing with GID and then executing a LIGGGHT's program.
After displaying information about elements that have 6 neighs, instead of the expected 5 neighs, it shows this:

ERROR on proc 0: Fix mesh: Bad mesh, cannot continue. Possibly corrupt elements with too many neighbors.
If you know what you're doing, you can try to change the definition of SurfaceMeshBase in tri_mesh.h and recompile (../surface_mesh_I.h:504)

Hey guys, I have done compression testing of particles in LIGGGHTS in 3D. Now, I want to do the same test in 2D. As per the documentation, I added command "dimensions 3" but I am getting an error while using "insert/rate/region" command and if I use "create_atoms" command by using the lattice for 2D, atoms are created, but the moment my wall touches the atoms, I get a message " Proc 0 Internal error", also in create atoms i am not able to add gravity. So, what is the correct procedure to model a simulation in 2D ?? and which visualization software is best to view it ??

Hi All,

I have a question related to the union of two region

In my simulation, I am currently defining a region as a sum of two adjacent cubes.
By looking at the .vtk of my simulation in paraview, I see that there is a small "empty space" (or gap) between the regions and I don't understand if

1) that comes from the division of the region (although it supposed to look like a single piece)
region regdown block 0.0 0.5 0.0 0.5 0.0 0.25 units box
region regup block 0.0 0.5 0.0 0.5 0.25 0.5 units box
region reg union 2 regdown regup units box

Hi All,

I have a problem/question about the servo wall

http://www.cfdem.com/media/DEM/docu/fix_mesh_surface_stress_servo.html

I want to first define two sub-regions, in which I want to insert two different particle distributions (pdd1 and pdd2 in the file).
After the distribution is complete, I want to insert a "servo - wall", from the top of the simulation box to compress both packings (pdd1 and pdd2)

Hey,

Dear All

I have a big problem with calculation time. I tried to simulated particles with 1 mm diameter but it takes too many times.

I think my problem is skin distance in neighbor command. How I can calculated optimized skin distance.

Regards
Esmaeil

Hello everyone,

For my thesis it was asked me to obtain the timestep of each simulation calculating it from the contact time (tc = pi / omega), for which I need stiffness and viscosity.

If I am using a pair style "hooke" and my inputs are Young, Poisson, Restitution , Friction and Characteristic Impact Velocity, is there a way to access the variables "k_n" and "gamma_n", when Liggghts has calculated it?

Thanks

Greetings,
Luca