How to insert initial positions for multispheres?

Submitted by Andrea Mellado on Mon, 04/06/2020 - 17:10

Hi,

I would like to know if it is possible to define the initial position of a multisphere in LIGGGHTS (eg. placing a cube in the bottom of a tank) instead of inserting it at random places in a domain?
Also, in the "multisphere_stone_restitution" example, I did not understand how the atoms' positions were defined: in the "stone1.multisphere" file, the x, y, z coordinates are all positives, but when I output the results in Paraview, the x and y coordinates are negative. How are the atoms' positions actually defined?

Thank you for your time,
Andrea M.

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richti83's picture

richti83 | Tue, 04/07/2020 - 12:10

Hi Andrea,

Yes you can, but you need to modify fix_insert_pack slightly.
Here are my modifications: https://pastebin.com/SV21GhHm
(search for insert_at)
You'll need to add these lines in fix_insert_pack.h after line 99 too:

//set points at
double px_, py_, pz_;
bool insert_at;

recompile LIGGGGHTS.

In your input script you can than use:

fix ins$a rigid_group insert/pack seed ${prime} distributiontemplate pdd1 insert_every once vel constant 0 0 0 &
overlapcheck no particles_in_region 1 region reg ntry_mc 1000 atP ${Px} ${Py} ${Pz}

Where a,Px,Py,Pz are variables from file or any calculation.

I've made this chain out of clumps:
https://www.youtube.com/watch?v=WgvQwANB480&list=UUAq71PznyKqvyvlNnKJr0a...

Good luck and stay healthy,
Christian

I'm not an associate of DCS GmbH and not a core developer of LIGGGHTS®
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Andrea Mellado | Sun, 04/12/2020 - 01:12

This helps me a lot! Thank you!

gpru | Mon, 05/10/2021 - 16:43

Dear Christian,

I had the same problem, which I wanted to solve by the modifications you provided in this thread, unfortunately the link seems to be out of date, are those modifications still within reach and would it be possible for you or anyone else to share a new link?

My sincerest apology for messing in this thread, however I guess for the solution to be helpful for others like me, an upgraded link would be much appreciated.

Best regards
Gunnar