LIGGGHTS® - User Forum

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.

Hi everyone,

Are there any commands to see how many particles are in contact with a wall? Or in the code, which part can give a output for the number of particles on a wall? I see the fix mesh/gran command. It can only output the force and torque.

Thanks a lot.

J.Wang

Dear LIGGGHTS users,