Menu

Discussion Forum

New Discussion
Filtrer

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

1/r in 2D-axisymmetric volume force: How to deal with it on the axis?

Posted 10 juil. 2019, 13:10 UTC−4 Low-Frequency Electromagnetics, Computational Fluid Dynamics (CFD) Version 5.4 3 Replies

Milad Saadat
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi all, I'm simulating ferrohydrodynamics and I'm trying to impose a Volume Force in the Laminar Flow physics. This volume force has a part like this:

((1/r)(d(r(d(A,r))^2,r))+d(d(A,r)d(A,z),z))mu0_const

where "A" is the magnetic scalar potential. When I plot this term, the closest layer to the axis has not been taken into account actually (take a look at the attached image please, the black vertical line is the axis.) How can I prevent this problem? I have instabilities on the axis because of this issue. Thanks

Attachments:

3 Replies Last Post 10 juil. 2019, 17:03 UTC−4
Edgar J. Kaiser Certified Consultant
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 5 years ago 10 juil. 2019, 15:41 UTC−4
Updated: 5 years ago 10 juil. 2019, 15:40 UTC−4

Milad,

the 1/r term goes to infinity at the axis (r=0). You need to prevent that some way, maybe by adding a constant>0 in the denominator: 1/(r + const). And you need to be aware that the symmetry does not allow any nonzero radial component at the axis.

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Milad, the 1/r term goes to infinity at the axis (r=0). You need to prevent that some way, maybe by adding a constant>0 in the denominator: 1/(r + const). And you need to be aware that the symmetry does not allow any nonzero radial component at the axis. Cheers Edgar
Milad Saadat
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 5 years ago 10 juil. 2019, 16:25 UTC−4
Updated: 5 years ago 10 juil. 2019, 16:24 UTC−4

Edgar Thanks for your response. This term is a divergence from a field, that's why it makes 1/r. Consider the continuity equation for instance: how this equation is written in 2D-axisymmetric? Does the COMSOL itself prevent 1/0 by adding a constant to its denominator too? Thanks, Milad

Edgar Thanks for your response. This term is a divergence from a field, that's why it makes 1/r. Consider the continuity equation for instance: how this equation is written in 2D-axisymmetric? Does the COMSOL itself prevent 1/0 by adding a constant to its denominator too? Thanks, Milad
Edgar J. Kaiser Certified Consultant
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 5 years ago 10 juil. 2019, 17:03 UTC−4
Updated: 5 years ago 10 juil. 2019, 17:03 UTC−4

Comsol isn't modifiying your expression. You need to take care of cases like this by yourself.

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Comsol isn't modifiying your expression. You need to take care of cases like this by yourself.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content