LIGGGHTS® - User Forum

Hello,

I am trying to model flow of grains through a slit under confining pressure (imagine sand grains in a fracture confined under a certain pressure). The way I'm doing this is by creating two rigid walls made of atoms arranged in a lattice with a force applied to each atom. However, once I create the lattice and apply the rigid command, all atoms in the lattice are returned with NaN or -NaN in the dump files after the first step. Code is attached.

I know I'm just missing a simple step. Ideas?

Thanks,

Roman

I am trying to run a simulation where particles are poured into a thin, tall container. I had the idea to begin pouring (with insert/rate/region) near the bottom, and move the insertion region vertically as the pile of grains grows. This is so that they won't have to fall all the way from the top of the box to the bottom.

However, when I try to run a simulation like this, it stops after a few insertions. By "stops", I mean it seems to get caught in an infinite loop somewhere. If I pour from a non-moving region, this problem doesn't arise.

Dear users,

last week I posted about problems with my ball mill simulation. The problem was that the balls adhered underneath the lifting bar of the stl geometry. I was told to improve the mesh because of high skewness and aspect ratio.

After I've done it, the problem still remains! The balls still adhere to the bar!

I will attach the new mesh, so you can check it.

Please tell me what the real problem is and what do I have to do to solve it.

Thank you!

Kind regards,

Eugen

Dear all,
I could not find any info on how to record to dump file
moving walls defined with:
fix myoscillatingwall all wall/gran/hertz/history 3 0 zplane 0.0 NULL 1 wiggle z 0.001 0.02
I had supposed that since I only need a simple movement
like this I could skip building a mesh, but how can I
export the wall position (to read it in paraview)?
Note that the wall works as intended, the particles
correctly interact with it.
Thank you,
Alessandro

Velocity Verlet integration assumes that acceleration only depends on position , and does not depend on velocity. Then is it logical to perform Velocity Verlet integration on granular where there is velocity dependent terms in formula of force and consequently acceleration depends on the velocity?

Thanks

I have been wondering if it is logical to perform fix nve or fix nve/sphere on a pack of frictional grains? since in the case of friction energy can not be conserved and is lost in each collision. but all the sample input files that I have seen in the example directory of liggghts are integrated in with NVE.

Hi everybody

Im currently modifying the movingMesh example to learn how to use Liggghts
Till now I have being able to modify the region geometry, size of particles, particles insertion region, etc

But now I got stuck when I try to apply the wall/gran fix to the stl file that I defined. The program simply crashes.

Does anyone detect where is my mistake?

Here is the scrypt:

atom_style granular
boundary m m m
newton off

communicate single vel yes
units si

#region reg block -.1 0.6 -.1 0.2 -0.3 0.25 units box
region reg cylinder z 0 0 .06 -0.1 .3 units box

Hi,
Does anyone is now using the gran/hooke/history/stiffness command?
I am using it but system warned:
[localhost:13166] *** Process received signal ***
[localhost:13166] Signal: Segmentation fault (11)
[localhost:13166] Signal code: Invalid permissions (2)
[localhost:13166] Failing at address: 0x7fc06aa59000
[localhost:13166] [ 0] /lib64/libpthread.so.0(+0xf500) [0x7fc06fe13500]
[localhost:13166] [ 1] liggghts() [0x51681c]
[localhost:13166] [ 2] liggghts() [0x59761b]
[localhost:13166] [ 3] liggghts() [0x4fe93b]
[localhost:13166] [ 4] liggghts() [0x426a34]

Hi

Im able to run the simulation and in paraview observe the mesh created through stl file.
Also I changed the scalefactor from 1 and 0.1 and was able to appreciate the difference in size of the mesh.

My problem is the offset. I tried to move the mesh by changing the xoff, yoff and zoff, but nothing happens. The mesh always stays in the same place.

Have someone had the same kind of problem?

Hi everybody,

I'm looking for an effective way to generate a dense bed of spherical particles in a 2d simulation.
I hoped that fix_pour_dev_packing could be used for that - also the doc says that - but since one has to use fix_particledistribution_discrete together with fix_particletemplate_sphere which cannot be used in 2d simulation it seems to be not possible.

Is there any other way to generate dense packing in 2d simulations effectively instead of simulating all the pouring process?

Thanks for the help,
kind regards,

Sebastian