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Equation Subscripts

Posted Dec 1, 2021, 6:44 a.m. EST Low-Frequency Electromagnetics Version 5.5 2 Replies

Sahil Maharaj
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Hi,

I'm creating a model using the electric currents interface of the AC/DC Module, and I'm slightly confused by some of the conservation equations. The first equation presented in the charge conservation node is . According to the module users guide, Q is the resistive loss, but I'm unsure of what the subscripts j and v refer to. Are they the directions? I'm doing a 2D axisymmetric model, so the coordinate directions are usually referred to as r and z, hence my confusion.

Also, the second equation is . According to the users guide refers to external current density. But since I'm not using the external current density node, can I just ignore this part of the equation? Since I'm assuming the default value is 0.

Any help with this would be appreciated.

Thanks, Sahil

2 Replies Last Post Dec 10, 2021, 9:59 a.m. EST
Durk de Vries COMSOL Employee

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Posted: 3 years ago Dec 1, 2021, 7:29 a.m. EST
Updated: 3 years ago Dec 1, 2021, 7:38 a.m. EST

Hi Sahil,

Thanks for asking! In this context, "j,v" refers to "Current source, Volumetric" (Q is a source, j is a current, v refers to "volumetric"). This variable should have the unit A/m³. There are also surface current sources and line current sources, for example. If you wish to know more about a variable, you can also have a look in the "equation view".

Je is the external current density. You can consider this a "right-hand side" of the equation, or a means to excite your model. By default its value is zero, but you can set it to some other value using the "External Current Density" domain condition that you mentionned. In most cases, one would excite an Electric Currents model with Ground and Terminal conditions though.

Kind regards, Durk

Hi Sahil, Thanks for asking! In this context, "j,v" refers to "Current source, Volumetric" (*Q is a source, j is a current, v refers to "volumetric"*). This variable should have the unit A/m³. There are also surface current sources and line current sources, for example. If you wish to know more about a variable, you can also have a look in the ["equation view"](https://doc.comsol.com/5.5/doc/com.comsol.help.comsol/comsol_ref_modeling.10.56.html). Je is the external current density. You can consider this a "right-hand side" of the equation, or a means to excite your model. By default its value is zero, but you can set it to some other value using the "External Current Density" domain condition that you mentionned. In most cases, one would excite an Electric Currents model with Ground and Terminal conditions though. Kind regards, Durk
Sahil Maharaj
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Posted: 3 years ago Dec 10, 2021, 9:59 a.m. EST

Ah, that makes perfect sense. Thanks for your help!

Ah, that makes perfect sense. Thanks for your help!

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