LIGGGHTS® - User Forum

I am a fresh user of LIGGGHTS just trying to install the program today. I have downloaded the liggghts package via git including the lpp (git clone git://cfdem.git.sourceforge.net/gitroot/cfdem/lpp mylpp) but just can't get any example started after this stage. Do I still need to do a sudo-apt get install before i can get it working? Please help

Hi everybody,

I'd like to calculate the hydrostatic pressure in a cylinder filled with granular particles on its cylindric wall.
I think the command

fix xxx all mesh/gran/stressanalysis xxx.stl ...

is not an appropriate measure to calculate these forces, because by outputting the forces on the mesh with f_xxx[1], f_xxx[2], f_xxx[3] I get the total forces in these directions. That means I get the sum of positive and negative forces and the result will be somewhere near zero...

How could I proceed instead?

Thanks in advance,
kind regards,

Hi, everybody

I'm new liggghts user,
I need to create a planar face for the fix insert/stream but i dont know what are the specifications for making the insertion face

Hi Christoph,
I want to compress the particles after they are poured completely in a cylinder. But the moving wall does not affect the particles and it move through the particles means particles are not resisting the moving top-wall. My input script is:

atom_style granular
processors 1 1 1
atom_modify map array
boundary m m m
newton off
echo both

communicate single vel yes
units si
region reg cylinder z 0.0 0.0 0.07 0.0 0.751 units box
create_box 1 reg
neighbor 0.001 bin
neigh_modify delay 0

#Material properties required for new pair styles

Hallo to everybody,

right now I'm trying to verify experimental results of a so called "uniaxial compression test". In this test, a present pebble bed is compressed by a slowly moving wall until reaching a specific strain rate (1,25 % in this case). While compressing, the effective force on the wall is measured.

These results have already been verified using another DEM-Software.

Now I'm trying to verify these results using LIGGGHTS. My results highly deviate (about factor 300) from the existing verified ones, though.

Hi,
Does anybody have an updated version of restart2data tool?

After using 1.5.2:
pair_style gran/hertz/history 1 0 #Hertzian without cohesion
pair_coeff * *
write_restart restart.chute3DPBC_init

I get the following from restart2data:

Reading restart file ...
WARNING Restart file version does not match restart2data version
restart2data version = 15 Jan 2010
ERROR: Unknown bond style ?ctive

Hi Christoph
i want to simulate a compression test. First particles are poured into a 0.5 m high cylinder without topwall, result is saved for restart; and now i want to add a top wall and want to move it to compress the particles, but i am getting an error while restarting the file that it can't open restart file onef1.restart (onef1.restart is the name of restart file) . Can you help me?
Thanks,
NIKHIL

Hallo,

quick question:

is it possible to change properties like youngs modulus (which I defined right at the start of my simulation with a fix_property/global command) at a later stage of simulation?

I first tried it by simply unfixing the previous command and then redefining it again with fix_property/global and the new value. This procedure resulted in multiple "WARNING: Dangerous build in triangle list" and as a consequence my particles disappeared out of my simulation box.

Hi All,

I am trying to use the "simple" version of gran/hertz/history (gran/hertz/history/stiffness) but I am unable to run on the current version on Liggghts (1p5p3). I have provided a simple example code below.

When I run using an older version (1p2p9) it appears to work well, however with 1p5p3 I receive this error:

ERROR: Could not locate a fix/property storing value(s) for gamman_abs as requested by (null)

The problem is that I am using hertz (not hooke) so I should not need gamman_abs. If I define gamman_abs and gammat_abs, I receive this error:

I want to have two types of granular atoms, one with properties of glass and the other a ceramic, how do I do that? I know that the Youngs modulus etc has to be set with the fix command with as many values as there are atom types. But how do I declare there to be two atom types?

Sorry for the basic nature of my question - I know DEM but still grappling with LIGGGHTS commands and fluency.