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Fail to evaluate the derivative at a line

Posted 21 août 2012, 01:35 UTC−4 RF & Microwave Engineering Version 4.0, Version 4.2 2 Replies

Bruno Berg
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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 3 déc. 2012, 10:09 UTC−5
COMSOL Moderator

Hello Bruno Berg

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Jan Kaul
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Posted: 1 decade ago 2 déc. 2012, 11:12 UTC−5
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)
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Posted: 1 decade ago 3 déc. 2012, 10:09 UTC−5
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

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