LIGGGHTS® - User Forum

Hello,

Can anyone let me know like what are the limitations/restrictions of LIGGGHTS code?
Like particle size, is this code valid for nano-sized particles also?
I know there is "vol_limit" , is there any specific answer for choosing "vol_limit < 1e-12" ?
If I change to "vol_limit < 1e-20", is the code still valid? or do I need to change any properties?

If possible please let me know the limitations of LIGGGHTS code.

Thank you.

Hi ,

I tried to use hybrid granular molecular to simulate multisphere systems, the atoms are successfully read, and I used fix rigid infile to define the center of mass, and moments of inertia. Initially, the non-spherical bodies are uniformly distributed in the simulation box, with a volume fraction of about 0.1, and the first few thousand time steps are running fine (time step = 1e-6), however, the simulation box will increasing after several thousand of time steps, and I can see the total amount of atoms are decreasing.

Hi all,

I am running a rotating mill with 1 atom, velocities and positions are read from a read_data file. It runs and the behaviour of the atom is as expected, but the time it takes to finish the simulation is way too long, obtaining 0.23 seconds per iteration.

If I keep all the same settings but insert the particle with the insert/stream command, the time is much smaller, such as 0.005 seconds per iteration.

Hello,
I recently updated my LIGGGHTS-Version to 3.2.
One of the many features is the temperature can be assigned when the particle are created.
But unfortunately, I can't find any examples of this function.
If someone can give me one, it would be great.

Best regards
RobertG

Dear all,

attached to the post you find an input deck with my attempt at creating a rotating drum which is just a cylinder of a fixed diameter and length. In order to achieve wall friction I inserted a fix,namely

fix cyl_wall1 all wall/gran model hertz tangential history primitive type 1 ycylinder .09 0.0 0.0

The computation runs smoothly, but doesn't show what I expect. For those of you with greater experience my error might be obvious, but let me explain my thinking:

I want to simulate shear mixing in a twin-screw geometry, but I am facing two problem:
1. after particle insertion, they don’t see the STL walls, so they often cross kneading discs, and other time the barrel, which I have not been able to understand why. Doubting the role of smaller time step requirement, I check time step suitability using check/timestep/gran to be sure that time step is not undesirable, changed location of particle introduction to avoid wall interference, but still not able to figure it out.

Hello together,
I have only an short question.
Is it possible to read a value, which is used in the fix porperty/global command, from an external file.
If it is possible, it would be nice if someone can give me an example.

Best regards
RobertG

Dear all,

firstly as a new user I like to say Hello!

Although I understand the ideas of DEM pretty well, my programming skills with respect to C++ are practically in-existent. From what I understood by reading the manual and 1 or 2 entries in the Forum, my problem may need some programming, but please correct me, if I am wrong.

Hi all,

I am reading atom positions from a text file without any error to run a rotating mill case. When I visualize my results I see that the particles are in the correct position but only the ones in contact with the geometry of the mill move due to its motion.

I wonder if this is because I have not set any velocity in my text file.

So I tried to add velocity in the file, in a correct format apparently but I cannot find the way for LIGGGHTS to understand it.

Any comments would be appreciated. I am attaching the data file used.

Thanks in advance,

Dear All,

I have two doubts about cohesion model sjkr.

1) In the cohesion model, what is the reference for cohesion energy density values? How do we select the values
for cohesion energy densities? Can we calculate it, if we know the properties of liquid and solid?

2) Cohesion model uses JKR model, and it adds only an additional normal force. What about tangential force?

Any help will be much appreciated.

Thanks,
Narendra