LIGGGHTS® - User Forum

Hi All,

I have a problem/question about the servo wall

http://www.cfdem.com/media/DEM/docu/fix_mesh_surface_stress_servo.html

I want to first define two sub-regions, in which I want to insert two different particle distributions (pdd1 and pdd2 in the file).
After the distribution is complete, I want to insert a "servo - wall", from the top of the simulation box to compress both packings (pdd1 and pdd2)

Hey,

Dear All

I have a big problem with calculation time. I tried to simulated particles with 1 mm diameter but it takes too many times.

I think my problem is skin distance in neighbor command. How I can calculated optimized skin distance.

Regards
Esmaeil

Hello everyone,

For my thesis it was asked me to obtain the timestep of each simulation calculating it from the contact time (tc = pi / omega), for which I need stiffness and viscosity.

If I am using a pair style "hooke" and my inputs are Young, Poisson, Restitution , Friction and Characteristic Impact Velocity, is there a way to access the variables "k_n" and "gamma_n", when Liggghts has calculated it?

Thanks

Greetings,
Luca

Hi,

I am trying to extract information of contacts between particles from LIGGGHTS.

Contact Normal Forces, tangential forces, position, vectors, particle id contributing to each of the contact points.

Please give some idea how to do so from the software. Any information regarding these will be helpful.

Thanks in advance.

Dear all,

The stress/atom just calculate the pair stress between particles,not including the pair stress for the wall and particle. For my case, the pair stress between wall and particle is very important.

Is it possible for the developer to update this recently?

If not, how should I modify the pair.cpp, only the simple process is Ok.

Many thanks,

Leo

Hi everybody,

I am trying to "move" a primitive zplane along the x axis.

The command I am using is:
fix primZPLANE all wall/gran model hertz tangential history primitive type 2 zplane 0 shear x -0.05

When I leave out the part "shear x -0.05" I receive no error at all. As soon as I add it, the error I get is:
"ERROR: Expected floating point parameter in input script or data file (../fix_wall_gran.cpp:285)"

What am I doing wrong?

Best regards,
MiRa

Hi Everyone,

I am new to LIGGGHTS. In my simulations I have calculated some variables (they are averaged values) and I would like to dump them in the dump file.
Among the tutorials, forum and manual I mostly see that LIGGGHTS dumps information in one file per timestep (100 files = 100 tsteps), but i would like to have one big file with each line representing each timestep.

Does anyone have any suggestion or example?

Greetings
Luca

Hi Everyone,

I am looking for a way to use the timestep as if it is equal to 1/40 of the contact time (given stiffness and viscosity it should be possible to obtain the contact time).
Is there a built in function or should I compute it via variable?

Greetings
Luca

Hi, I'm running the simulation of steel particle sedimentation.
In the input file of LIGGGHTS, I think that the unit of 'YoungsModulus' is [Pa] in SI unit.
But, when I write the steel's mechanical property(about 200GPa = 200.e9) on particle and aluminium property (about 68.9GPa= 689.e8) on the wall,
the calculation results is so weird. (The particle's rebounded force is very large...)
I want to know the definite unit of YoungsModulus in the input file.
Thank you

bc