Question about the addfroce command and the size of the box

JF's picture
Submitted by JF on Tue, 01/18/2011 - 17:31

Hi all,

I have two questions:

Do you know how should I use the command (fix addforce) to push a group of spheres ?
Because this command only works during an energy minimization, but I don't understand the minimize command (it is a specific command for atomic simulation).

During a tensile test on a granular sample, it is possible that some spheres are outside the box initially defined. Do I need to change the size of the box during the simulation or there will be no errors ?

Regards
JF

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ckloss's picture

ckloss | Tue, 01/18/2011 - 17:41

Hi JF,

>>fix addforce...only works during an energy minimization
No, it also works during time-stepping. It just adds a constant force (the new LAMMPS version, which will be integrated in the next major LIGGGHTS release, can also handle variables) - see your local doc for details.

>>it is possible that some spheres are outside the box initially defined.
>>Do I need to change the size of the box during the simulation or there will be no errors ?
If a particle is outside the simulation box when a neigh list is built, it is lost. This can be desired in order to have a fixed simulation boundary (e.g. hopper discharge). If you dont want particles to be lost, you can choose to extend the simulation box so that all particles are encompassed. See the doc of the 'boundary' command for details.

Cheers,
Christoph