LIGGGHTS® - Developer Forum

Hi Christoph!
Thanks for the new release! I noticed something in fix breakparticle/force-code, which is buzzing me. In the fix_breakparticle_force.cpp:362 v_ins is defined, but it is never used (?). Instead v_insert is used in set_x_v_omega(...) (fix_breakparticle_force.cpp:371), which is (0,0,0), if it is not given in start-up script. Correct me if I'm wrong, but shouldn't the created particles have a momentum conserved velocity, instead of zero velocity what they now have?

Thanks,
Timo

Dear all,

yesterday I played around with several compiler flags to see their effect on execution speed of LIGGGHTS. I measured the execution time of the example movingMeshGran in LIGGGHTS 1.4.6 on my desktop machine (Intel Core i7-2600 with 8GB RAM, gcc 4.4.3) with the command

time liggghts < in.movingMeshGran > /dev/null

Results:
no optimization: 1m27.898s
-O : 0m55.417s
-O2 : 0m47.635s
-O2 -ffast-math -march=native -funroll-loops : 0m44.454s
-O2 -ffast-math -march=native -funroll-loops -finline-functions: real 0m44.415s
-O3 : 0m47.273s

Hi,

I have several questions, and would be grateful if someone could answer them.

1) I was wondering if anyone could point me to where in the code, the variable "c_history" (tangential displacement between a particle and the mesh) is saved IF a particle slides to another element. i.e. so that tangential displacement will not suddenly adopt the value zero if a particle slides along a flat plane.

I apologize in advance for not knowing how to do this -- I would imagine this is pretty simple for someone who knows what they are doing (this excludes me, apparently):

I am trying to develop a sintering interaction (pair_gran_sinter.cpp) for LIGGGHTS 1.4.6, and I need to ensure that it is conserving particle volume as the particles sinter together (see movie below for example). To do this, I need to store an array of initial particle sizes (radii) such that it is available to pair_gran_sinter.cpp for subsequent volume and updated radius calculations.

Hi!
Now I'm trying to write the fix, which would create a new particle as particles are near to each other, i.e. A+B->C type of reaction. So would the best strategy be to take from fix_bond_create_gran.cpp the list building and implement it on the fix_insert_pack.cpp ? As I understood the atom positions are gone through in
void FixBondCreateGran::post_integrate()
and the insertion of the particles in
void FixInsertPack::x_v_omega
Am I correct? Or is there some more complicated things, which I should consider?

- Timo

Hi!

Could anybody tell me where may I find the normal and tangential overlap calculations implementation? It would also be great if one could refer to some literature for the same.

Thanks in advance
TM

pair/gran/local does not save normal force

Hi everybody,
I have two questions
1. How to get the normal force at the contact, as the pair/gran/local only accounts for the shear force as mentioned by Jean in
node/212

2.The value of contact stress
conact stress sigma(alpha,beta)

sigma(alpha,beta)=1/V*[sum(i) sum(i neq j)*[rij(alpha)*fij(beta)/2]]

fij(beta)=fij(beta)_tangential+fij(beta)_normal

If normal force is neglected, will it give valid result for contact stress.

regards,
Samantaray

In case anyone finds it useful here is some information about a method I use to couple Liggghts with a separate Lattice Boltzmann code written in Fortran.

The Fortran code is the driver, so it starts first calculates the fluid flow, writes the particle information to a file and then calls an external subroutine to run Liggghts automatically from the command line for one time step. See the following link.c file:

#include
#include
int dem_(int i)
{
printf ("Checking if processor is available...");
if (system(NULL)) puts ("Ok");
else exit (1);

This is the link to the LAMMPS developers' manual - currently not very extensive but a good starting point. 99% of this apply to LIGGGHTS as well.
http://lammps.sandia.gov/doc/Developer.pdf

Christoph

Hi all,

if anybody of you is interested in a bonded particle model in LIGGGHTS, I have an early version that I can share. It is quite beta and comes without doc. If anybody of you is interested in working on improving that model to make it ready for release, just fetch the attached tarball.

Cheers,
Christoph