LIGGGHTS® - User Forum

Hi,

Hello,

I have met a problem by using restart. i have three related files. First one is for generating particles using "insert/pack", the second one is for making all paritlces settled in a box, the thrid one is for moving mesh box using "fix move/mesh" as follows:

"fix shear1 all move/mesh mesh top linear 0.005 0 0"

however I got following error message:

"ERROR: Illegal fix move/mesh command, illegal mesh ID provided (fix_move_mesh.cpp:63)"

acutally, i defined the mesh "box" in all three files using "fix mesh/surface/stress".

I just had a quick question. I hope it's okay. I am trying to do a comparison of the various forces present within my granular simulations and want to plot these in an excel spreadsheet.

I am using the gran/hertz/history pair_style but I am having problems seeing how the cohesionEnergyDensity is used. I cannot find mention of it in the manual so if anyone could point me in the right direction, or better yet let me know the equation that it appears in that would be really helpful for me!

Thanks!

Paul

Hi,

There were these two posts a while back:

node/100
node/193

but no updates since. I think that there is plenty of interest in the geomechanics community for stress control and membrane walls and I am wondering if these are still in the development pipeline.

Thanks,
Joe

Hi,

I'd like to set up a simulation with some clumped particles. In Version 1.5.3 my script startet with:

atom_style hybrid granular molecular

But if I want to start a simulation in Version 2.1 with:

atom_style hybrid granular molecular
or
atom_style hybrid sphere molecular

In both cases there is the message ERROR: Invalid atom style (atom.cpp:343).
Why this happens? Should i compile with some extra packages?

Best regards, Niels

I'm trying to run a simulation that uses two different atom types for the particles and for the walls. My code was based on a code that took its material properties from the meshGran tutorial in LIGGGHTS - ie, small young's modulus, only one atom type. I could get that code to run to completion (this simulation would fill up my hopper with particles and then empty them out in 150000 time steps, roughly 5 minutes).

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?