# Discussion Forum

## Electric Current

Hello Everyone,

I am currently simulating Joule Heating by applying Electric Potential and Ground boundary conditions at the corresponding boundaries of imported CAD geometries. There already is experimental data for some of the designs I am investigating, so it would be great to extract values for the electrical current to compare it with values measured with an multimeter. I know it has to do with Integration over the current density; my question would be how excatly would I approach this problem?

4 Replies Last Post 2024年2月28日 GMT-5 05:29

Posted: 3 months ago
Updated: 3 months ago

I'd use the electric currents (ec) interface and specify the potentials, much like you said. Don't forget that you'll need to specify the conductivity of the materials you are modeling. Mesh the geometry in sufficient detail. You can plot the current density in post-processing. You can integrate current density over a surface with using a pre-defined Probe (Definitions-->Probe-->Boundary Probe) or via post-processing, (Results--> Derived Values--> Surface Integration). Oh, and if you setup your potential surface as a "terminal", the integrated total current will be available in post-processing as the "terminal current." Ask more specific questions if you have other concerns.

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara

Posted: 3 months ago

To summarize: I would put a cross-section through which the current flows, that I can then integrate over either via a probe or in post-processing. That already helps a lot; Thank you. Could you however elaborate on the "terminal" setup? This is the first time I come across this term.

Posted: 3 months ago
Updated: 3 months ago
1. You can use your final (input or output) surfaces as the relevant cross-section; you don't need to introduce a separate surface just for the current to pass through (although that can work too, if you prefer).
2. The "Terminal" boundary condition (bc) is one of those available among the choices of bc's in the electrostatics (es) interface. Electrostatics --> Boundaries --> Terminal. You then have various types of terminals to choose from. When you are looking at something like that and want to know more, hit the F1 key to bring up context-sensitive Help. For example, when I do that, the Help system tells me (among other things): "The Terminal node provides a boundary or domain condition for connection to external circuits, to transmission lines, or with a specified voltage or charge. By specifying zero charge, a floating potential condition is obtained." And then there is plenty of additional discussion after that. But... ultimately, you'll need to experiment with the various settings, and also with the various post-processing options, to effectively increase your knowledge of this tool. Despite all the documentation and examples available, mastering (to the extent that is even possible) the use of Comsol Multiphysics requires a mix of curiosity, observation, practice, patience, and perseverance.
-------------------
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara

Posted: 3 months ago

Thanks again for the detailed answer.

I was able to get satisfying results.