Menu

Discussion Forum

New Discussion
Filter

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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.

Fail to evaluate the derivative at a line

Posted Aug 21, 2012, 1:35 a.m. EDT RF & Microwave Engineering Version 4.0, Version 4.2 2 Replies

Bruno Berg
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi,
I am using COMSOL 4.0 RF to model light scattering. In 2D model, i calculate a very thin sheet scattering, which is 1D geometry in such 2D model. So i use the surface current boundary condition for this 1D line, and at the same time, i use a weak form boundary PDE to calculate the current distribution. Generally, It is a coupling problem between 2D RF and 1D PDE. However, when i define a derivative at the weak boundary PDE, i.e., ux, i got the following error

Failed to evaluate variable Jacobian.
- Variable: ux
- Geometry: 1
- Boundary: 18

I have tested that, if i define the weak PDE (also 2D), there is no problem, and the weak expression can be performed. So i think the key problem is that the derivative along this 1D line. Any suggestion will be greatly appreciated.


Best
Bruno
2 Replies Last Post Dec 3, 2012, 10:09 a.m. EST
COMSOL Moderator

Hello Bruno Berg

Your Discussion has gone 30 days without a reply. If you still need help with COMSOL and have an on-subscription license, please visit our Support Center for help.

If you do not hold an on-subscription license, you may find an answer in another Discussion or in the Knowledge Base.

Jan Kaul
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Dec 2, 2012, 11:12 a.m. EST
Hi,

I've got a similiar problem on a 1D-Geometry Comsol doesnt seem to have the derivatives ux,uy,uz although i try to compute the derivative in z direction. Do I need to use a special local Coordinate system or is there another way of doing it?

I really appreciate your help

Jan Kaul
Hi, I've got a similiar problem on a 1D-Geometry Comsol doesnt seem to have the derivatives ux,uy,uz although i try to compute the derivative in z direction. Do I need to use a special local Coordinate system or is there another way of doing it? I really appreciate your help Jan Kaul
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Dec 3, 2012, 10:09 a.m. EST
Hi

but in 1D you can only have one derivative along "X" the two perpendicular are =0 by definition.

But if you are in 3D and you select an edge you might have derivatives along x,y,z, but if the edge is on the border of two or more materials then how can you define the derivative there ?

If you are in 2D a geometrical Edge is a boundary entity, there you have an up/down derivative and a mean one that can mostly be defined

--
Good luck
Ivar
Hi but in 1D you can only have one derivative along "X" the two perpendicular are =0 by definition. But if you are in 3D and you select an edge you might have derivatives along x,y,z, but if the edge is on the border of two or more materials then how can you define the derivative there ? If you are in 2D a geometrical Edge is a boundary entity, there you have an up/down derivative and a mean one that can mostly be defined -- Good luck Ivar

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