perodic boundary condition in LIGGGHTS

Submitted by Oliver.pasqual on Thu, 04/05/2012 - 08:51

hi, everyone
I have a puzzle in the using of periodic boundary condition in the setting of particle flow.
the simulation box is cubic ( x:0~0.1, y:0~0.04, z:0~0.1).
I want to take a periodic boundary condition in the y direction, I dealed with it with the following steps:
firstly pour the particles and the related settings is:

boundary f f f
fix xwalls all wall/gran/hertz/history 1 0 xplane 0. 0.1 1
fix ywalls all wall/gran/hertz/history 1 0 yplane 0. 0.04 1
fix zwalls all wall/gran/hertz/history 1 0 zplane 0.0 0.1 1

after a long time's run all the particles stop at the bottom of the box, and then write the parameters into a restart file.
the another script read the restart file, and then the boundary condition is changed in this step, related setting is:
boundary f p f
fix xwalls all wall/gran/hertz/history 1 0 xplane 0. 0.1 1
fix ywalls all wall/gran/hertz/history 1 0 yplane 0. 0.04 1
fix zwalls all wall/gran/hertz/history 1 0 zplane 0.0 0.1 1

I am puzzled whether 'fix ywalls' is needed to be set with '0 0' to make the friction_damp_flag inactive, or it has no effect even the friction_damp_flag is activated just because it is a periodic boundary condition.
thanks in advance
Oliver Pasqual

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ckloss's picture

ckloss | Thu, 04/05/2012 - 09:14

Hi Oliver,

the boundary settings specified in the restart input script will be overwritten by the settings in the restart file (you should get a warning about that).

One strategy to solve the problem would be to use fix insert with "all_in yes" and use the periodic boundary condition from the beginning on - that's how I typically do it

Cheers, Christoph