LIGGGHTS® - User Forum

I'm trying to make a triaxial compression test in two scripts. First, generating particles using insert/stream in a cubic region then unfix all walls and save a restart file. Second, fix new servo walls and apply equal pressure from all walls except the base wall and after reaching the target confining pressure, I only increase the pressure of the upper wall to apply vertical compression on the sample. I use kp = 1, ki = 0, kd = 1e-6.

My problem is that some steps takes too much time especially the compression steps. Here is the output timings:

I am still trying to run a simple shear flow. Since nvt/sllod was not carried over from LAMMPS, I am wondering if anyone knows any alternatives. Following LAMMPS guide for a simple shear, I can run a simulation with a deforming triclinic box with remap set to v. Normally, the nvt/sllod integration would update the velocities, positions, and control the temperature.

Hi all,

i have to questions regarding friction coeffcient. First, why is the upper limit for the friction coeffcient = 1?
There are plenty of materials that have a friction coeffcient greater 1 in literature.

Second question is a bit more special. How can i implement a model that allows for friction coeffcient's greater than 1? And also would it be possible to implement a friction model that allows to set the friction coeffcient in relation to the normal force that act's on individual particles?

Thanks a lot for hints!

I'm trying to simulate a triaxial test (compression) on a cubic sample surrounded by 6 mesh faces. Only the top face will move in (-ve) z direction to compress sample while the other 5 faces are stationary. I want to draw the stress-strain curve for this sample to get the yield and ultimate stresses. My problem is that during compression the stress is only increasing and never decrease. I think this is because the lateral deformation for the sample in the other two directions (x,y) is not allowed.

Dear Support Team, I am following the installation/compilation instructions as provided in the documents section.
At --2.2.2. Steps to build a LIGGGHTS(R)-PUBLIC executable-- when I do "make auto", I am getting the following error:

$ make auto
Creating list of contact models completed.
/usr/bin/sh: -c: line 1: unexpected EOF while looking for matching `"'
/usr/bin/sh: -c: line 2: syntax error: unexpected end of file
make: *** [Makefile:114: auto] Error 1

I am trying to change the group particles are assigned to based on their location in the simulation. I can do this as a one time thing, but I want to keep doing it throughout the simulation. Consider just a periodic box with particles randomly moving. If I want to separate particles into different groups based on y location, I can use

variable loc1 atom y
variable loc2 atom "y > 0.5"
variable loc3 atom "y < 0.5"
group top_group variable loc2
group bottom_group variable loc3

Hi everyone,

I am trying to perform a quasi-static uniaxial compression of an assembly made of a cubic box with inside 5000 particles randomly distributed with a radius of 0.00025 meters.

I am realizing this by using the "fix deform" command and a double loop. The external loop is for compression, the internal one for dissipation of kinetic energy realized with the "fix viscous" command.

I try to simulate an assembly with two group of particles. However, there is only one group of particles (ins1) added to the simulation while the other (ins2) is ignored. My code is given below. Could anyone tell where I did wrong? Thank you!

atom_style granular
atom_modify map array
boundary m m m
newton off

communicate single vel yes

units si

region reg block 0.0 2.0 0.0 0.1 0.0 1.0 units box
create_box 2 reg
group nve_group region reg

neighbor 0.001 bin
neigh_modify delay 0

Dear all,

Hello,

I am implementing heat transfer for granular media. I need to set two different temperatures: one for the boundaries(stl file) and another for the particles.
Is there any tutorial that can help or any other suggestion?

Thanks in advance,
Clara