LIGGGHTS® - User Forum

Hello all. I am fairly new to LIGGGHTS and I have been trying to run a very simple simulation of two spheres in contact under load by method of compaction. I am simply using two .stl walls (bottomwall and topwall) and compact the two spheres my moving the topwall and keeping the bottomwall constant. I am able to view the simulation in paraview and I see the top wall moving; however there is absolutely no interaction with the particles.

My input file:

Hi LIGGGHTS users,

I want to do some simulation in order to validate the CODE with my experimental data. My experimental findings are related to static granular packings in which radius of particles are varied from 0.1mm to 16mm. I used this command to check time step but i get different values for different diameters:

fix ts_check all check/timestep/gran 1000 0.1 0.1

For example this warning is printed during simulation, the value is constant for one kind of diamtere.

WARNING: time-step is 31.483188 % of rayleigh time

Hello.
I have a question about the normal dissipation force model for gran/hertz/history pair_style.
From LIGGGHTS documentation and source I see what

F_dissipation = -gamma_n * relative_vel_n

where

gamma_n ~ (S_n*m_eff)^(1/2),
S_n ~ Y_eff * (R_eff*delta_n)^(1/2).

So,

F_dissipaton ~ (Y_eff)^(1/2) * R_eff^(1/4) * delta_n^(1/4).

But as I know, and as follow from ref.[Brilliantov] (see eq.(17)) from the manual, it should be:

F_dis ~ Y_eff * R_eff^(1/2) * delta_n^(1/2).

Whence is this discrepancy?

I'm interested in simulating magnetic particles in a media. How can I add this force as a source term in liggghts, which force can be derived analytically, f(x,y,z) or
solved by a FEA solver. For simplicity, I neglect a dipole-dipole effect between particles. Thanks in advance for your guidance.

I could not resolve particle penetration to any walls. What mistake did I make? Below is a code that I worked on. This code will be coupled with the CFDEM.
Thanks in advance for your help.

===
echo both

atom_style granular
atom_modify map array
communicate single vel yes

#boundary f f p
boundary f f f
newton off

units si

region reg block -0.0002 0.0002 -0.0002 0.0002 0 0.0004 units box
create_box 1 reg

neighbor 0.00008 bin
neigh_modify delay 0 binsize 0.00008

#Material properties required for new pair styles

Hi all,

I am trying to run a simulation with a rigid body (using fix rigid). When I output from the fix (using a variables) the x-axis velocity, force, and torque are always almost zero (order e-322). The other output data appears reasonable. Does anyone have any ideas?

Here is a basic example code:

#System Information
boundary f f f
newton off
communicate single vel yes
units si
echo both
neighbor 0.01 bin
neigh_modify delay 0
timestep 5.0e-6

#Atom Information
atom_style granular
atom_modify map array

#Create Atoms

Hi guys,
Has anyone seen this warning before?
"One or more atoms are time integrated more than once"
I use a rigid body (by fix rigid command) to add confining presure to my direct shear test. I have explicitly exclude the atoms of that rigid body when doing the time integration, as suggested in the manual.
For example, I want to integrate a group of atoms excluding the rigid body, I assign:
1. region_1 and group_1 for the atoms I want to integrate
2. region_2 and group_2 for the rigid body I don't want to integrate

Hi

I am trying to apply forces on atoms based on one of their coordinate positions. I have implemented this type of force successfully on a single atom using

run 50000 every 10 "fix acforce all addforce ${Force} NULL NULL region ac"

where

variable Force equal (variable function(v_xposition))

I have introduced additional atoms into the system using

read_data grann

in which I specify their positions, initial velocities, etc

To my understanding I require

Hi

I'd like to set up a simulation for a dense suspension (volfrac: 0.6). To reduce the complexity of the model I'm trying to include the fluid phase with "pair_style lubricate". This pair style is part of the colloid package. And it seems to me, that this package was not installed when I installed LIGGGHTS. Playing around to with the atom_style command I found out that the following atom_styles are missing:
- colloid
- dipole
- ellipsoid
- peri
and my guess is that these packages are not installed.

HI!

I wanted to change the angle of the chute in the after 8000 runs. Therefore I did the following
....
#the chute
fix cad3 all mesh/gran chute.stl 6 1.0 0. 0. 0. 0. 48.3 0.
fix movecad all move/mesh/gran rotate 0. 0. 0. 0. 0. 1. 7.0 cad3
......
fix granwalls all wall/gran/hertz/history 3 0 mesh/gran 5 cad1 cad2 cad3 cad4 cad5
......
fix ins1 nve_group pour/dev mass 3.888 10001 distributiontemplate pdd2 region bc massflowrate 0.5554 vol 0.6 20
......
run 8000 upto
unfix ins1

unfix cad3
unfix movecad
fix cad3_l1 all mesh/gran chute.stl 6 1.0 0. 0. 0. 0. 52.5 0.