LIGGGHTS® - User Forum

I've a question about computing the maximum contact force
I know I can get the pair-force with
compute 2 all pair/gran/local force
But How to calculate the magnitude ?
(I tried variable fmag atom sqrt(c_2[1]^2+c_2[2]^2+c_2[3]^2) but got ERROR: Mismatched compute in variable formula)

Next problem is how to find the maximum of fmag, I tried
variable fmax equal max(fmag)
but got "ERROR: Invalid special function in variable formula"

Hi Chris,

I created a large region compared to the radii of particles, and the time-stepping becomes very slow.

region reg block -0.01 8.1 0.0 1.51 -0.01 4.51 units box

The particles radii varies from 0.008 to 0.016, and total # of particles is 10k. So the region is mostly empty.

I tried using shrink-wrapped "boundary s s s" but the issue remains.

Hello everyone,
I have been using Liggghts for a couple weeks and I have already done a simple shear test but now I want to do a triaxial test. I read about the servo control walls but since the test is a cylindrical moving boundary I dont think that is a proper boundary because of two reasons:
1. The walls are rigid boundary and in reality they are flexible.
2. I can not think of moving the cilindrical walls with out changing the shape or leaving a gap.

Hi everyone,
I tried to give the wall an angle velocity with "fix move/mesh" command. It gives as "fix c1 all move/mesh mesh cad1 rotate/variable origin 0 0 0 axis 1 1 1 omega 0.5". However, the result shows "ERROR: Variable name 1 for fix move/mesh rotate dynamic does not exist (mesh_mover.cpp:329)". Does anyone know how to modify it? My LIGGGHTS version is 2.2. Thanks.

Hello everyone,

Could anyone be kind to tell me how to define a group based on particle diameter? Say, "group sub diameter <= A".

In the newest version of LAMMPS, this could be done by using 'variable' keyword with group command, as described in http://lammps.sandia.gov/doc/group.html

However, in the current version of LIGGGHTS (2.3.6), the 'variable' keyword cannot be used with group command.

Thank you in advance!

Lei

Hi all, I am trying to create a wall in Liggghts in gran style to track the particle-wall interaction force. Well I want my wall be tilted for 45 degrees, so not perfectly xplane or yplane or zplane.... and also can move horizontally forward with constant velocity. basically it looks like this. \ ------> A tiled wall moving in horizontal direction. I don't see how to set it through fix wall/gran command. Is it possible in Liggghts? I am not expecting it to be very difficult....

Thanks for any reply.

xiuhan

HI Hello friends, I am new to this and would like to know how to install LIGGGTHS in ubuntu 12.04 ?

Thanks!! :D

Hi,

Edit: Deleted. Just needed some sleep... ;-)

Regards,
Paul

Is there a simple way to change the speed of a conveyor (surface velocity).

The only thing I can think of is to start with one fix mesh/surface with a certain surface velocity. stop the simulation and write a restart file.
Restart the sim with a new surface velocity...

I'm sure there is a better way though.

Thank you for your help,

Kirk

Hi,

I have been running my simulations with 2 cpu's and I use

write_restart restart-%-*.rstrt

to create a restart at the end of the simulation.

I was wondering if I can restart with a different number of cpus. I would like to use 6 now. my read_restart looks like

read_restart restart-%-*.rstrt

Whould I have more luck if I used

write_restart restart-*.rstrt

and

read_restart restart-*.rstrt

instead?

Thank you,

Kirk