LIGGGHTS® - User Forum

Hi

I am using multispheres in my simulation. I have created variables because i would want certain quantities to be printed to screen as the simulation proceeds however i am getting an error "Variable command group may not be used together with fix multisphere". May someone assist on how i should use variables in a multisphere simulation

Thank you

I need to insert spherical particles of size varying from 0.0001m to 0.00001m (diameter) into a container until the container fills completely. Without feeding no of particles as input data how can i formulate the syntax for this condition.

Hi everyone,

I am learning how to use the fix rigid command. From my trials, the fix rigid command requires a dense particle clump. If the particles are separated from each other, the rigid body of particles will collapses due to collision with other particles. Am I right?

Thanks
Weijing

Hi every one,
please help me i am new user of liggghts, and using ubuntu 16.04 LTS operating system.
i used the procedure given in the link : "https://www.cfdem.com/media/DEM/docu/Section_start.html"
after completing step 0 (2.2.2. Steps to build a LIGGGHTS(R)-PUBLIC executable) i got lmp_auto in src directory.
than i went directly on "2.6. Running LIGGGHTS(R)-PUBLIC"
and tried to run tutorial example chute wear input script by using following command in terminal:
":~/LIGGGHTS-PUBLIC/examples/LIGGGHTS/Tutorials_public/chute_wear$ mpirun -np 4 lmp_auto

Hi, where can I find more info on the following listed change for 3.7:

"Arno Mayrhofer (DCS ) modified the fix move/mesh command that now has reference frames (for the center of rotation) that depend on parent fixes"

Thanks.

[edit]
The reason I asked, is that my stacked rotations are now all being combined into a single rotation. That is, the reference frames all stay the same, when I've been using a rotating reference frame to essentially run my x y and z rotations separately.

Hi guys,

I"m kind of newbie to this program and have lots of questions on using it.

First of all, I have trouble with the fix property/* command.

In the manual, it says that 'variablename = a valid C++ string' does it mean that I can use any of the variable name which I want to set?

If it is correct, then how can LIGGGHTS program understand all those variables and set the property?

And if there's any list of variables that I can use for the fix property/* command, please let me know.

Thanks,

Regards,

hello,

I am using dump local/gran/vtk command as follow to visualize forcechain in paraview:

dump forcechain all local/gran/vtk 1000 dump*.vtk

However, I get the following error:

ERROR: dump local/gran/vtk requires 6 arguments (../dump_local_gran_vtk.cpp:94)

Unfortunately, I cannot find any information about this dump style in online documentation of LIGGGHTS 3.X (The online manual). I would appreciate if anyone could tell me what arguments are needed for this dump style.

Thank you,
Nina

Dear DEM users,

I am struggling with an error which has been keeping at a position for several months. I am current modeling a large number of particles, e.g., 190K and 400K particles using a 40 cores computer. The diameter ranges widely from 0.01mm to 1.0mm. The major problem of this simulation is "Neighbor list overflow, boost neigh_modify" which indicates there are too many particles in the neighbor list. I have changed lots of parameters including the skin, the number of processors, the friction and reconstitution coefficients... but no one works.

I'm trying to model a structure sitting atop a granular assembly of multisphere particles. The structure is modeled as 1 large box-shaped multisphere particle containing about 300 constituent spheres. The structure as a whole extends across about 3 to 5 processor sub-domains in a simulation run with 80 or more cores. My problem is that when I insert this structure, the number of ghost atoms increases from about 100,000 to 1,000,000. The simulation becomes considerably slower, and the run time increases by a factor of about 20.

Hi there,

I am getting a "WARNING: One or more atoms are time integrated more than once" which I believe I have tracked down to two lines:

fix fu all move variable NULL NULL NULL NULL v_Vy NULL units box
fix gravity all gravity 9.81 0 -1 0

i.e., I am doing a gravity and also a forcing via a variable Vy. My results are looking a bit odd, so I am wondering if I should instead incorporate the gravity into the fix move? i.e. making the value "v_Vy - 9.81*time" instead of "v_Vy"?

Or is it fine to have this warning?