integrated quantity functions
Hello,
I want to define an expression with a nonscalar variable, (it would be a source, S=j*V), where j is the current density and is a 3Dvector). If I try to define an expression I get an error telling that I haveto use integrated qunatity functions. I have been trying to get a tutorial, reading manuals and so on, but I haven't been able to understand what I have to do. If any one could help me. Thanks in advanced. 
What are the full expressions? Are you trying to do Joule heating?

Hi,
No I'm trying to simulate an electrical contact resistance as a source on the energy equation. The expresion that I want to define for that sorce has to be Sarea= j (vectorial sum of the current density, A/m2)*V(a certain value of voltage, a constant, for example 19V) And I don't know how can I get the vectorial sum of the j and how to use it as a variable. Thnak you very much 
I think you'll need Additional Variables (AV) to do this. J is equal to the conductivity multiplied by the gradient of the electric potential (I think, pls check!). So you'll need an AV for the electric potential then another AV for J.
The AV for electric potential should be a scalar AV, set to solve Poisson Equation, with the Kinematic Diffusivity equal to Electrical Conductivity/Density. You'll probably need to add in a factor to get the units correct. The AV for J will be a vector AV, with the X component equal to: Electrical Conductivity*Electric Potential.Gradient X 
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