LIGGGHTS® - User Forum

Hi Iam a new user in liggghts. While doing one of the example insert stream, an error came that is not understood by me. I am attaching the command file, model and log file that iam doing.

Hi to all
I would like to use DEM to simulate the pushing of a granular soil due to a compressive
force from one of it's sides.
This subject is Geotechnics is called the stick-slip phenomenon. We have done the experiments on a box
filled with beads to simulate the granular soil. The box is open from the top but one of it's sides is a moving
wall that can be pushed towards the granular medium with a constant compressive force. Progressively in time
a line somewhere in the middle will develop to show where the soil will break.

Hi all,

I need to implement a DEM simulation involving capillary force between particles. I use a hooke/stiffness contact model.

The capillary force model is the Willett model:

Willett, C. D., Adams, M. J., Johnson, S. A., & Seville, J. P. K. (2000). Capillary bridges between two spherical bodies. Langmuir, 16 (24), 9396–9405.

The capillary force is given by a liquid bridge that is created when two particles come into contact and persist until a rupture distance is reached.

The first step (of a long path) is:

Hi all,

The manual describes about volume_limit of fix/particletemplate/sphere that LIGGGHTS will throw an error if the particle volume too small compared to machine precision. My question is how to adjust machine precision with default limit 1e-12 of LIGGGHTS. For examples, I'm playing with particle's size D=50micron that has volume of 5.4e-14 m3. It's obviously lower than default value. Does it cause serious error to simulation result?

Dear All,

In my simulation ,I am trying to print out all data from the command .. wall/gran/local .. to be in one txt file but I could not.

In Pre-atom or global data, It can be defined in (variable equal command) and then use (fix print command) to store all the data.

I am looking to print (local data) in one txt file (like print do). Is there any way to do that?

thank you in advance for your help.

Regards.
Chris

Hi all,

I am trying to calculate the total number of contacts.
In my simulation, I used( compute contact/atom command) to calculate the number of contacts. Then, I used (fix print command )to store all the data in order to sum all the numbers and get the total number of contacts.

variable C1 equal c_NOC
fix cont all print 10 "${C1}" file contact.txt screen no
compute NOC gr contact/atom

Hi All,
I am a new user.
I implemented the following simulation [in.packing]:
Box with periodic boundaries filled with 9261 particles with size and velocities read from data file I created [data.packing].
I am using a linear spring dashpot contact model. Quantities are scaled in such a way that are dimensionless: M=10-9 kg, L=10-3m, T=10-6s.

I acquire the dump files in Matlab and, for each particle, I compute the overlaps with other particles and the elastic forces (output from LIGGGHTS) acting on it.

Hi everyone,

Hello, I've done a few simulations trying with 1, 4 and 8 processors, and I got higher calculation time for 4, and even more, for 8 processors. In the input script, I tried two thing. First I didn't set any parameter for "Processors", and then I try with several combinations. I noticed that I could get better calculation time chosing aproppiate values in "Processors", but it is not better than a single processor. I read the recomendations in the manual where is explained what to do to get better performance.

I want to calculate residence time distribution of a system. I used the following lines in the script:

region rtd block 0 0 0 0.01 0 0.01 units box
fix rt all property/atom/tracer region_mark rtd mark_step 1000 marker_style dirac check_mark_every 1000
compute nparticles all nparticles/tracer/region region_count rtd tracer rt
fix extra all print 100 $nparticles file rttd.txt

but this error occurs:
ERROR on proc 0: Substitution for illegal variable (input.cpp:410)