LIGGGHTS® - User Forum

I am currently doing my research on metal 3-d printing and I was hoping if anyone can help me set up a powder bed using liggghts.
Thanks in advance.

I'm trying to simulate particles with radius 0.0002m (200 micrometers). If I used "SI" units the required dt is about 1e-6 second.

Does using "micro" units in liggghts instead of "SI" units accelerate the run time since the time unit in "micro" unit system is microseconds not second, so dt will be equal to 1 microsecond?

Is there any differences in the output results if simulating the same problem with different unit system?

I'm generating particles in script (1) then save a restart file. Then apply some forces on the particles in script (2) after reading the restart file.

My question is can I define different inter-particle interactions in script (2) without changing it in (1) or they must be the same since script (2) reads the restart file of (1).

I want to do that to avoid running script (1) each time I need to change these parameters to save time.

Hi,

Could you please explain how the hard particles (Event-driven) approach is implemented in LIGGGHTS? I couldn't find the details in the documentary and source code.

In the event-driven approach, usually the overlap of the particles doesn't happen, and the cohesion models are dependent on the overlap. So how can we use the cohesion models in hard particles?

I request to please provide the relationship between cohesion energy and surface energy used in literature in JKR models?

Thanks and regards
David

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