LIGGGHTS® - User Forum

Hello,

I am working on a rotating blade moving into a granular medium and would like to compute the force/torque exerted by the particles on the mesh. I use Liggghts version 2.1.1 and the fix "mesh/surface/stress".

My problem is that the output is invariably zero (see the helix.txt output file).
Can somebody help me finding the origin of the problem ?

The interesting part of my code is:


fix cad1 all mesh/surface file blade.stl type 1 scale 10 move 0. 0. 0.3
(insert particles and run some timesteps)

Hi,
I want to run a simulation of compaction of an open (low-density) packing. To save time I am confining my simulation to 2D by using a thin periodic slice. Any ideas on how to generate an open packing (say with a packing fraction of ~ 0.4) in this situation that is mechanically stable under gravitational load? If I just generate particles using insert/pack and let the particles settle under gravity they tend to crystallize and I obtain a rather dense packing.

Any suggestions would be appreciated,
Thanks,
Tapan

Problem: dense packing under gravity will not be formed even the particle velocities are nearly zero.
Conditions: insert particles more than a critical number.

tested versions 2.0.4, 2.1.1

I think this should be a bug where the gravity field is lost when the total particle number is larger than a critical value (I am doing test and will tell the critical value in the following given case).

Files attached: geometry (cubic.stl, extension has to be changed), input (in.packing, extension as well), and a result using liggghts 2.0.4.

Hi I'm interested in the effect of wall stiffness, I think I'm right in saying the LIGGGHTS using particle of infinite size to 'make' the wall, so if there of infinite size does it follow that their young's modulus will always be very high or even infinite?

As young's modulus = stress/strain
and strain = L/ Li

where Li is the initial characteristic length (the particle diameter) which in this case is infinite and thus the young's modulus must also be infinite, am I right?

Hi Christoph,

I have done such similar job by using commercial codes. There are 2 methods to generate a non-sphere particle: 1) cluster spheres together as a single particle, the bonds between spheres can be broken; 2) particle is formed by number of overlapping spheres as a rigid body, bonds can not be broken.

Since the feature 'multisphere' is not yet available in both 1.5.3 and the latest version, according to previous posts. So i was wondering, is it possible to bond spheres ( overlapping or non-overlapping) together using method 1 in Liggghts/Lammps.

Cheers,

Hi everyone!

I am aiming to get started using CFDEM and just finished setting up all components necessary for that. All in all I now have up and running:
- OpenFOAM-2.1.x incl. ThirdParty-2.1.x (built from source)
- LIGGGHTS 2.1.1
- CFDEMcoupling 2.4.4
- current version of lpp
I tested each part of the installation running the respective tutorial/example cases: OpenFOAM, LIGGGHTS and CFDEM seem to work as expected.

Dear all,

I'm trying to change the processor size after I save the result from a serial version of LIGGGHTS and want to run the parallel version to continue the results. I define the prossessor dimensions before the read_restart comand but it shows an warning and error message as:

WARNING: Restart file used different 3d processor grid
orthogonal box = (-0.00106955 -0.00106955 -6.95546e-05) to (0.00106955 0.00106955 0.00206955)
ERROR: Bad grid of processors

Dear LIGGGHTS Community,

I was just wondering if someone could explain me how to visualize or use the data calculated by the pair/gran/local function defined as :

compute forces all pair/gran/local id pos force
dump forcedump all local 400 post/dump.force c_forces[1] c_forces[2] ... c_forces[12]

I posted this a couple of weeks ago about my jobs stopping early. I'm trying to fill up a "2D" hopper with particles, remove the piece at the bottom, and let the particles drain out, but I would get some sort of error and my job would end early (and it seems like it always ends on timestep 77000 of X). The only response I received was to update to the latest version. I am now running LIGGGHTS 2.1, and I'm getting the exact same issues.

Hi there,

Im pretty much very new to all this and I have got all the files, programs and features up and ready. Is there any advice/tutorials/books I can look at for developing a DEM exercise to model a simple vibrating hopper with small to medium sized media (12-15mm Dia glass bead)?

If anyone can help, it would be much appreciated.

Many thanks

Gwyn