LIGGGHTS® - User Forum

Hello, Christoph,
I try to use the latest version of LIGGGHTS 2.3.2, but it doesn't work. Then I tried with an example from Liggghts - meshGran, and it doesn't work either. I uploaded the output and error meassage files. Could you take a look? Thank you!

Hi everyone,

I'm confusing with cohesion energy density in the pair_gran_hooke_history. As I understand cohesion energy density is the work needed to separate the whole volume of particle in contact. So how to calculate cohesion energy density if Van der waals adhesion is taken into account? And where is cohesion energy density in original JKR model?

Many thanks for your help!

Best regards,

Duy

Has anyone ever made an atom property (or assigned it to a region, changed its type, etc) based on a conditional statement?

For instance, if I set some threshold of particle force, say...
variable crit_force equal 50
then i find per/atom values of force magnitudes
variable mag_force atom (fx[i]^2+fy[i]^2+fz[i]^2)^0.5

from there I'd like to say something like...
if "${mag_force[i]} > ${crit_force}" then &
[set the atom, i, into a group, change the atom to type 2, etc.]


We are often asked what kind of computer is needed to do DEM-Simulation with LIGGGHTS.
I used every computer system in my local area to make a little benchmark.
All tests where done with the moving mesh example script** and Liggghts 2.2.3.

The Linux machines are running Ubuntu 12.04.1 LTS with mpich2 and GCC compiler.
The Windows 7|8 machines are running mpich2 1.4.1 and a cross compiled windows version*** (VS2008 compiler).

I've created a couple of small tools for generating STL files for some simple geometric constructs that I wanted to share in case anyone finds this useful. Basically, I got sick of going to a CAD program every time I wanted to create a simple regular frustum, rectangular bin, or simple plate. The attached codes are written in Fortran. Hope someone finds it useful.

Regards,
Chris

Hi, All:

I currently have a problem that needs to consider the position and number of particles with different sizes, so basically I am trying to calculate the porosity of the poured grains. For this target I need to know number of particles and the height of poured grains, so that I can calculate this property.

I am wondering if there is any existing examples using LIGGGHTS that can:
1. calculation of porosity
2. if there is not such a function, so how can I access (for example with python) some properties of particles after pouring

Hi, All:

I currently have a problem that needs to consider a type of particle that is composed of two bonded spheres (one with positive electric charge and one with negative charge), so basically I am trying to first bond particles together and then assign electric charges to them. (See attached figure)

I am wondering if there is any existing examples using LIGGGHTS that can:
1. simulate the electro-static forces between particles?
2. bond the particles together

Thanks for any suggestions in advance!

Roy

Hi,

In trying to calculate the number of contacts per particle, I found that contact/atom gives me the incorrect result. I have attached a simple test: 2 particles (particles #7 and #8) sandwiched between two layers of 3 particles. From coord/atom and from the contact force dump, each particle clearly has 4 contacting neighbors, yet contact/atom does not give this result (it gives 3). Any ideas?

Hello,

I did a simulation using force controlled doundaries. when i try to unfix it, then i got the erro message as follows:

ERROR: Fix mesh/surface/stress/servo (id zcover_1): illegal unfix command, may not unfix a mesh while a fix move is applied.Unfix the fix move/mesh first (fix_mesh.cpp:242)

but the problem is that i did not use fix move/mesh, why am i not allowed to unfix the "fix mesh/surface/stress/servo"?

Is there a way to restart a simulation that has fix move/mesh with the "wiggle" style, and have the simulation continue the oscillatory motion from where it left off? According to the docs (and some tests that I ran), the wiggle style uses X0 and delta from "the time the fix is specified" in the input file. In a restarted simulation, this time is *not* the same as in the original simulation that produced the restart file. I want the fix move/mesh motion to continue as if from t = 0, not t = whatever in the restart file.