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 The information provided may be out of date.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.

Defining Maxwell Stress Tensor as Global Equation

Please login with a confirmed email address before reporting spam

I have defined MST as Global Equations:
Txx-->Dx*conj(Ex)+Bx*conj(Hx)-0.5*(D*conj(E)+B*conj(H))
Txy-->...
..
Tzz

When I try to simulate it I get the following error message:
"Failed to evaluate variable Jacobian.
- Variable: E
- Global scope"

I think E(electric field) is defined in the RF Module as a variable.

Is there something wrong with my syntax?

Thanks a lot,
Damla

1 Reply Last Post Feb 16, 2011, 1:07 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Feb 16, 2011, 1:07 a.m. EST
Hi

I encounter such problems when I either
a) use by error some already defined COSMOL variables names
b) if I define some variables on a boundary and I use them on a domain

The latter is more tricky, when you define your variables, they can be defined locally or globally, they might have only a sens to be evaluated on a boundary, but you might need them globally (all over) to i.e. define a derivative (what is needed for the Jacobian) then you must use a linear or global extrusion to make your variable globally available, based on some mapping rule. Another way, but you need really to know what you are doing ;) is to use the nojac() operator, to exclude the variable from the Jacobian evaluation


--
Good luck
Ivar
Hi I encounter such problems when I either a) use by error some already defined COSMOL variables names b) if I define some variables on a boundary and I use them on a domain The latter is more tricky, when you define your variables, they can be defined locally or globally, they might have only a sens to be evaluated on a boundary, but you might need them globally (all over) to i.e. define a derivative (what is needed for the Jacobian) then you must use a linear or global extrusion to make your variable globally available, based on some mapping rule. Another way, but you need really to know what you are doing ;) is to use the nojac() operator, to exclude the variable from the Jacobian evaluation -- 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.