LIGGGHTS® - User Forum

Hello everybody,

I'd like to create my own simple STL meshes. Until now I did not use a mesh generator.
What is the simplest software to start with? (Gmsh seems a little bit too sophisticated for the beginning)

Thanks
Sebastian

Hello,

I have problems with understanding a few commands:

The simulation issue is a box filled with particles where I want to analyse stress on different heights of the walls.

I use these commands

fix cad all mesh/gran/stressanalysis cube 1 1 0 0 0 0 0 0 finnie yes
fix GlobalforceOnMesh all ave/time 50 2 100 f_cad[1] f_cad[2] f_cad[3] file filename.txt
dumpstress all mash/gran/VTK 200 post/dumpCAD*.vtk stress wear cad

Hi

I want to read in values from a text file so that I can control the speed of a rotational boundary condition that I have created (similar to conveyor - covered in another post). I want to read in two columns of numbers and assign each one to an array. This way I can calculate the speed based on the solution time. What would be the best (i.e. simplest and efficient) way of doing it?

Hello.
Is there a refs. where rayleigh_time and hertz_time expressions are derived?

And more, I see an error in the check/timestep/gran documentation.
In the doc:
dt_r =PI*r*sqrt(rho/Y)/(0.1631*n+0.8766),
But in code instead Y used shear_mod.

Also, for dt_h. In doc:
dt_h =2.87*(m_eff²/(r_eff*G_eff²*v_max)^0.2.
But in code instead G_eff used E_eff.

Hello.
What is mean of the frictionflag in wall/gran style?
I thought if the frictionflag is zero then the wall without friction. But the test showed that it is not.
In test script a sphere moves along yplane with given initial velocity. If yplane is frictionless then sphere's velocity should not be changed. But it is changing, see attached figs. And in different ways depending on the value of the flag.

And if I need frictional and frictionless walls should I to define 2 atomtype?
Thanks.

Test script:

#Particle packing by insertion and successive growing of particles

Hi,

I reinstalled my ubuntu distribution. I installed LIGGGHTS and everything worked properly (it compiled and created lmp_fedora). But when I want to execute lmp_fedora my terminal is reporting:

fuchsjosef@ubuntu:/media/Volume/LAMMPS/liggghts_1p2p9/src$ lmp_fedora
lmp_fedora: command not found

Maybe someone can help me
Josef

Hi,
I'd like to use different friction for different stl.
For example I'd like to set friction on stl 1 grater than stl 2.
I tried something like:
fix cad1 all mesh/gran/stressanalysis stl1.stl 1 0.001 0. 0. 0. 0. 0. 0.
fix cad2 all mesh/gran/stressanalysis stl2.stl 2 0.001 0. 0. 0. 0. 0. 0.
But it request me 2 atom types.
Have I to set 2 atom types?
If yes, how have I to set the friction between the 2 types: fix fr all property/global coefficientFriction peratomtypepair 2 value_11 value_12 value_21 value_22 ?

Hey all !

I was wondering if LIGGGHTS is capable of simulating a slurry mixture, or a melt of several ingredients.
I would like to simulate a rather dense mixture of several granular particles, which solidifies over time.

What , in your opinion, would be the best way to describe such a melt , if possible at all ?
what would be the most appropriate values for poisson ratio \ young's modulus, and coefficients of restitution and friction for such a mixture ?
(I know they are defined for proper solids, though i was thinking if there's any way of obtaining that limit of a melt somehow)

Hi all,
I'd like to view particles displacement.
I used compute displace/atom but I think it does not calculate what I want.
As you can see in attached picture I have the distance of particles from Origin.
When I run simulation and I move my particles, I obtain the same pictures!
I want to calculate the displacement of particles from their initial position, not from Origin.
I tried also fix store_coord command but without result (the vector in 0).
Any help?

Thanks in advance

Andrea

Hello,

To vary the particel temperature I'd like to access it by these commands:

variable ramp_temp equal 0.05
fix heattransfer all heat/gran 500

compute temp all property/atom Temp

variable d_Temp atom ${ramp_temp}*c_temp
fix Tramp all adapt 1000 atom Temp d_Temp

... which doesn't work...

The Manual says, that the compute needs per-atom quantities as input, which are stored by LAMMPS and Temp is not a per-atom quantity...

But what I don't understand is, why can I access the per-atom temperature by this command: