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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Voltage Dependent Resistor

Posted 2013年9月23日 GMT-4 00:58 Electromagnetics, Low-Frequency Electromagnetics Version 4.3b 4 Replies

Andrew Wang
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Hello;

I want to simulate a simple electrical circuit as an initial step of my main study. In my study, I need to define the resistors whose values depend on the voltage gradient across them. However, Comsol give me the error "Circular variable dependency detected."

I know that this problem can be solved using conservation of charge in each circuit node and I have previously wrote a code to solve it. But, I do not know how to use Comsol to solve it.

Any suggestion will be highly appreciated.

Best Regards,
Andrew
4 Replies Last Post 2013年9月29日 GMT-4 03:12
Lingling Tang
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Posted: 1 decade ago 2013年9月27日 GMT-4 09:35

Hello;

I want to simulate a simple electrical circuit as an initial step of my main study. In my study, I need to define the resistors whose values depend on the voltage gradient across them. However, Comsol give me the error "Circular variable dependency detected."

I know that this problem can be solved using conservation of charge in each circuit node and I have previously wrote a code to solve it. But, I do not know how to use Comsol to solve it.

Any suggestion will be highly appreciated.

Best Regards,
Andrew


first, which physics mode you used? the ciruit mode (cir) or electric current node ?
second, the error is circular variable dependency detected", it means in your model the resistor is defined as a function of the voltage (gradient), while the voltage is defined as a function as the resistor (from Ohm's Law), that is the so called "circular variable". the variable in your model shall be changed someway. See something in the tutorial of "superconductor" model in ACDC mode, it may help you understand the problem.
Good luck!
[QUOTE] Hello; I want to simulate a simple electrical circuit as an initial step of my main study. In my study, I need to define the resistors whose values depend on the voltage gradient across them. However, Comsol give me the error "Circular variable dependency detected." I know that this problem can be solved using conservation of charge in each circuit node and I have previously wrote a code to solve it. But, I do not know how to use Comsol to solve it. Any suggestion will be highly appreciated. Best Regards, Andrew [/QUOTE] first, which physics mode you used? the ciruit mode (cir) or electric current node ? second, the error is circular variable dependency detected", it means in your model the resistor is defined as a function of the voltage (gradient), while the voltage is defined as a function as the resistor (from Ohm's Law), that is the so called "circular variable". the variable in your model shall be changed someway. See something in the tutorial of "superconductor" model in ACDC mode, it may help you understand the problem. Good luck!
Andrew Wang
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Posted: 1 decade ago 2013年9月28日 GMT-4 23:01
Hello Tang;

Thank you for your helpful reply. I studied the tutorial for "Superconducting Wire" which is a kind of similar story. However, I do not have any idea for my case since it is a DC circuit and resistances change with the potential difference across the resistors. By the way, I use Electric current mode (cir) in my model.

I really appreciate if you can help me with any idea.
Hello Tang; Thank you for your helpful reply. I studied the tutorial for "Superconducting Wire" which is a kind of similar story. However, I do not have any idea for my case since it is a DC circuit and resistances change with the potential difference across the resistors. By the way, I use Electric current mode (cir) in my model. I really appreciate if you can help me with any idea.
Lingling Tang
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Posted: 1 decade ago 2013年9月29日 GMT-4 02:13

Hello Tang;

Thank you for your helpful reply. I studied the tutorial for "Superconducting Wire" which is a kind of similar story. However, I do not have any idea for my case since it is a DC circuit and resistances change with the potential difference across the resistors. By the way, I use Electric current mode (cir) in my model.

I really appreciate if you can help me with any idea.


I guess you use the electric current(ec) mode instead of circuit mode(cir).
You may need to first study the tutorial ,
www.comsol.com/model/computing-the-resistance-of-a-wire-12697
then try to do some modification to achieve your goal.
[QUOTE] Hello Tang; Thank you for your helpful reply. I studied the tutorial for "Superconducting Wire" which is a kind of similar story. However, I do not have any idea for my case since it is a DC circuit and resistances change with the potential difference across the resistors. By the way, I use Electric current mode (cir) in my model. I really appreciate if you can help me with any idea. [/QUOTE] I guess you use the electric current(ec) mode instead of circuit mode(cir). You may need to first study the tutorial , http://www.comsol.com/model/computing-the-resistance-of-a-wire-12697 then try to do some modification to achieve your goal.
Andrew Wang
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Posted: 1 decade ago 2013年9月29日 GMT-4 03:12
Hello Tang;

Thanks again for your reply. I should first correct myself that I am using the Electric circuit mode (cir) in my study. I went through the example you sent. In this example, the resistor is made of copper which has constant properties such as reference resistivity. Therefore, it is totally different than my case and in fact it is a resistor with constant resistance.
Hello Tang; Thanks again for your reply. I should first correct myself that I am using the Electric circuit mode (cir) in my study. I went through the example you sent. In this example, the resistor is made of copper which has constant properties such as reference resistivity. Therefore, it is totally different than my case and in fact it is a resistor with constant resistance.

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