LIGGGHTS® - User Forum

Hi evereyone,

I have a naive question. I try to generate a random cubical sphere packing by iterative growing from a cloud of spheres.
But I have two problems :

1) I don't know, How can I indicate the growing increment at each step for the spheres.
2) I don't know, if it is possible to put this increment equal to zero when the solid fraction or the compacity reaches a fixed value.

if you have few indications to give me, please don't hesitate.

Thanks

Regards
Jf

Christoph,

What do I do wrong using the "fix/rigid" in a LIGGGHTS simulation? I tried to produce the same input for LAMMPS and LIGGGHTS but I get an error with LIGGGHTS: (Line numbers are on) This input is for LAMMPS; for LIGGGHTS line 9 is commented out and line 10 and 15-19 are uncommented.

Thanks,
Christian

==========
1 # Simple rigid body system
2
3 atom_style granular
4 newton off
5 communicate single vel yes
6 units si
7 neighbor 0.002 bin
8

Hi Everyone

I am running a model of a drum with spheres in it. The drum is imported from an STL file. When I run this, I get the following warning repeatedly:

"WARNING: Dangerous build in triangle neighbor list."

Do I need to be concerned with this? Is there perhaps a problem with the STL file? I did notice that my spheres might be escaping the drum, but I need to double-check for a reason.

I could only find the following in the "fix_tri_neighlist.cpp" file:

//if a fix move/mesh/gran is registered, advise the user to increase skin safety (and eventually shorten time-step)

Hi everyone,

I added this command in my file in order to move the top wall:

region topwall plane 1. 1. 1. 0. 0. -1.0 units box vel 0. 0. -0.1

I must define the interactions between the wall and the particles with this command:

fix wall1 all wall/region topwall gran/hooke 1.0 1.0 0.002

But I think that there is an error on the type of interaction (style). How can I define these interactions ?

My second question is: How can I get the normal force applied on the top wall or directly the normal stress ?

Regards
Jf

Hi everyone,

I would like to know, How I can integrate the position of spheres into my simulation ?
I have ready created a sphere packing and I want to use it.

I know that I must add this line into the fle in.mysimulation
# Read data

read_data position.sys

The file position.sys need to be writen like that ? (look the line under)
Please, can you correct ( position.sys) it in order that it works.
Thanks
Regards
Jf

LIGGGHTS Description

1 spheres # number of spheres

T atom types
# type of atom = granular ?

Hi Everyone

I want to make a drum with a horizontal center-line and "fix pour" spheres into it.

1) If I pick the Z-axis for this center line and gravity pointing to -Y, then I get:

"ERROR: Gravity must point in -z to use with fix pour in 3d"

2) OK, so I pick the X-axis for this center line and gravity pointing to -Z, then I get:

"ERROR: Must use a z-axis cylinder with fix pour"

Hi,

i am a newbie to LIGGHTS. Is there any example how to begin with it? Can anyone send me some small example how to start with LIGGGHTS. I have some experiences with PFC but i dont know how to get GUI or how to manage the toll.

Many thanks

cizek.ji@centrum.cz

Hi all,
I have imported two meshes into simulation region. One is base of cylinder and the other is cylindrical wall. I want to find stresses on cylindrical mesh only. But LIGGGHTS dumps all meshes. Is there a same way to group a particular imported mesh and then dump into file?

Thanks in advance,
Ram

Hi everyone,

First congratulation for LIGGGHTS. The installation was easy and the first example (cohesion) runs very well.
I am a beginner in LAMMPS and I'd like to understand a lot of things to build my DEM simulations.

I hope to be able to integrate my developpments (contact laws, …) into LIGGGHTS in order to perform large simulations.

Hello again!

I got an unexpected behavior with the "fix mesh/gran":
Originally I wanted to rotate a plane around the z-axis but nothing happend (F_fl0 in the example). Then I tried to rotate the plane around the y-axis (F_fl2 to F_fl6) but there is an additional (unexpected) rotation around the z-axis ... not what I wanted ...
Workaround would be to change the .stl-file ...
Regards,
Christian

==========
# Example:
atom_style granular
dimension 3
boundary m m m
newton off
communicate single vel yes
units si
region R_gesamt block -0.5 0.5 -0.5 0.5 -0.5 0.5 units box