LIGGGHTS® - User Forum

Hi all,

In the discrete element method, the normal contact between two spheres i and j has the same direction than the n-axis (in the local reference (n,s,t)).Thus, it is possible to compute the angular orientation of the particle "i" following the s-axis and t-axis (tethai_s and thetai_t) in the global reference (x,y,z).

To compute tethai_s and thetai_t in the global reference (x,y,z), I do:

thetai_1 = omega[i][0] * dt;

thetai_2 = omega[i][1] * dt;

thetai_3 = omega[i][2] * dt;

Hi all,

I am trying to restart a heat transfer simulation. I failed and thus I created a smaller problem, where I have the same problem, using the example heatTransfer_2. Please find two input scripts for liggghts below: in.heatTransfer and in.restart. in.heatTransfer writes a restart file after it is done integrating and then in.restart reads the restart file. Visualizing the output with paraview showed that the temperature is not read from the restart file.

Could you tell me, what I am doing wrong?

Hi Christoph,

I saw that the commands : read_restart and restart can save and reload a simulation.
However, I would want to know if these commands also save and reload the values held by the array "shear" (contact history).

Regards
JF

Hey everybody,

after installing Liggghts on Fedora 14 the following error message occurs when I try to start liggghts:

liggghts: error while loading shared libraries: libmpi_cxx.so.0: cannot open shared object file: No such file or directory

I have installed the newest version of openmpi and the mentioned file can be found in /usr/lib/openmpi/lib

I attach a screenshot.

Thanks for your help!
Andre

Hi all,

I have two questions:

Do you know how should I use the command (fix addforce) to push a group of spheres ?
Because this command only works during an energy minimization, but I don't understand the minimize command (it is a specific command for atomic simulation).

During a tensile test on a granular sample, it is possible that some spheres are outside the box initially defined. Do I need to change the size of the box during the simulation or there will be no errors ?

Regards
JF

Hi, all

I am thinking and finding if there is a rotation viscosity(damping) or rotation constraint command in LIGGGHTS, which may allow realistic description of granular flow behavior.

I have found a fix momentum command which allow me to zero angular momentum every several steps, but it is not what I want.

Any response from you will help! Thanks a lot!

Best,
Tong

Hi Everybody

I wanted to set the friction to different values, depending on where the particle is in the model, e.g. in a hopper, and in the process below the hopper.

My approach was to:
- define a region, REG_hopper
- associate a group of particles with this region
- set the friction first for "all", and then for the group using "fix property/global"

The steps below shows only the applicable commands:
region REG_hopper block x_lo x_hi ... z_lo z_hi units box
...
group GRP_hopper region REG_hopper
...

Hello everyone,

As it is my first question of the year 2011, I take this opportunity to wish all LIGGGHTS' users a Happy New Year.

About my question, I would like to know if it exists a Pizza's function to export the data from the custom dump to txt files ?

Each line of txt file will be the numerical data dumped for one atom. I need these txt files to perform posttreatment with Matlab.

Regards
JF

Dear Christoph,

There's a bug (Illegal if command) in early version of lammps, and it has been fixed in current lammps. However, the bug is still in liggghts. I used the patch file to liggghts that applied in lammps and it didn't work.

So could you help me to fix this? The patch file of lammps has been attached.

Many thanks!

Best,
Tong

Hi Christoph,
I am looking for further information about your force models in LIGGGHTS. Is there some special literature you used for development of the force models?
Happy new year and best regards, Josef