LIGGGHTS® - User Forum

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?

Dear all,

I come back to this topic again. I had time last week to make some test cases for multisphere.
I upload one of them.

LIGGGHTS360 was used for this simulation. The multisphere was only composed with two particles.

what I did was:
1. make a packing in a region with a stepped wall, saved as a restart file.
2. restart the case from the saved restart file and simulated it further using a moving wall.

Hi,
I have a problem with multisphere particles simulation.
when i use same case for simple spherical particles mixing, my results are good but when i used multisphere particles ( 2 or more sphere clumped together to form particle) then particles becomes cohesive and no mixing occurs between particles. i created multisphere particles according to code given in following link
https://www.cfdem.com/media/DEM/docu/fix_particletemplate_multisphere.html

Hi there,

I'm new to LIGGGHTS but I have been trying to use buoyancy and am getting odd results. I have read the documentation of 'fix buoyancy' and I am not sure about why dim level must be positive.

Documentation:
dim value = x or y or z
x, y, z = define the water level as x=const, y=const, z=const plane
level value = lev
lev = water level in length units, along the axis defined by dim

Hi,
I'm trying to simulate the heat generation inside the particles due to a nuclear reaction.
Is there a command to set a constant heat generation to the particles?

thanks

Simone