Rotation

Submitted by shahabgol on Wed, 12/10/2014 - 13:32

Dear all,

I have a question about "rotate" command in LIGGGHTS.

The geometry in my work consists of two separate parts. The first one is rotating around a specific axis and the second one is rotating around the first geometry part.
For the first part, there is no problem but how can I simulate rotation of the second geometry part around the first which rotates itself?

Regards,
Shahab

Forums:

richti83's picture

richti83 | Wed, 12/10/2014 - 15:03

use two rotate commands for the 2nd geometry, one for the reference frame-ratotion (should be euqal to the movement of the first body) and one for its own rotation.
Here is an example for one geometry:
http://www.cfdem.com/comment/13006#comment-13006

The move commands are superposioned in the order they are in the input skript. (fix1 rotates the local reference frame, fix2 is in the first frame, fix3 is in the 2nd frame and so on)

I'm not an associate of DCS GmbH and not a core developer of LIGGGHTS®
ResearchGate | Contact

shahabgol | Sun, 12/14/2014 - 11:26

Thank you for your kind reply.
I am confused a little. My LIGGGHTS version is 2.1 and it has problem with "fix rotcad1 all move/mesh mesh cad1 rotate/variable" in the "rotate/variable" part. rotate/variable is an unknown command. Is this problem related to the version or something else?
By the way, how can LIGGGHTS recognize "fix rotcad2 all move/mesh mesh cad1 rotate/variable origin 0. 0. 0. axis 0. 1. 0. omega v_omega2" rotates the geometry around rotcad1 while the origin is a fixed point (0,0,0) and does not change with time? Could you please explain a little more?

Regards,
Shahab

richti83's picture

richti83 | Mon, 12/15/2014 - 10:11

Version 2.1 is realy old and does not have /variable move command, you should update to 3.0.6 or don't use /variable. Be carefull: rotate/variable uses omega while rotate without /variable uses period as rotational velocity.

When two or more move mesh fixes are aplied to the same geometry, liggghts moves the reference frame with the first command and calculates the new orign and axis for the 2nd move mesh command. You need to define the initial origin and axis to let liggghts know where to transform the center of rotation for the 2nd move command.

I'm not an associate of DCS GmbH and not a core developer of LIGGGHTS®
ResearchGate | Contact

j-kerbl's picture

j-kerbl | Mon, 12/15/2014 - 10:17

Hi,
the latest LIGGGHTS version is 3.0.6
it can be downloaded from https://github.com/CFDEMproject/LIGGGHTS-PUBLIC
A guideline how to use git can be found here:
http://www.cfdem.com/system/files/githubAccess_public_LIGGGHTS_2.pdf

Then those commands should be recognized!
Beware, the style of some commands has changed slightly, most important is the pair_style.
You can look at the manual and the tutorial examples tough.

Cheers
Josef

shahabgol | Mon, 12/22/2014 - 15:24

Thank you for your kind replies.
If I download and install LIGGGHTS 3.0.6 what should I do to recompile CFDEM coupling without problems?
can I work with CFDEM 2.1 again or should I install next versions?
how about OF version?

Regards,
Shahab Golshan