LIGGGHTS® - User Forum

hi, everyone
I have a puzzle in the using of periodic boundary condition in the setting of particle flow.
the simulation box is cubic ( x:0~0.1, y:0~0.04, z:0~0.1).
I want to take a periodic boundary condition in the y direction, I dealed with it with the following steps:
firstly pour the particles and the related settings is:

boundary f f f
fix xwalls all wall/gran/hertz/history 1 0 xplane 0. 0.1 1
fix ywalls all wall/gran/hertz/history 1 0 yplane 0. 0.04 1
fix zwalls all wall/gran/hertz/history 1 0 zplane 0.0 0.1 1

Hi Christoph,
I have seen discussion in the forum about reading and outputting the contact forces between particles using compute pair/gran/local and the dump local command,
but I notice the compute pair/gran/local command can only output f_x, f_y and f_z respectively,
can I possibly output the normal contact force? If yes, how?
Also, I know that the current pizza can't convert the dump file of this compute to .vtk file, is there any method to do the conversion?

Thanks in advance.

Hi Christoph,
Following your reply in a post "how to speed up DEM"
I have taken a look at my timing statistics, and it seems the "other time" takes up the most of the time consumed.
Pair time (%) = 312.239 (32.578)
Neigh time (%) = 9.10633 (0.950124)
Comm time (%) = 16.8501 (1.75809)
Outpt time (%) = 0.128907 (0.0134498)
Other time (%) = 620.111 (64.7004)
Do you have any idea what is the "other time", How do I reduce it?

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