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How to use variables from solution in materials for representing nonlinear materials

Posted Jun 15, 2010, 6:46 a.m. EDT 1 Reply

SURYASIVAPRAKASH ALAPATI
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I have a small doubt on using nonlinear characteristics in comsol 4. In materials section while using soft iron, i want to define normB value from solution like mod1.mf.normB. But i am getting error message saying undefined values if try to solve.
I tried to define a constant like 0 or 1 instead of mod1.mf.normB, its working without errors. But it will take linear magnetic characteristics. I am attaching the file here, please check the material contents of the soft iron normB value.
Please help me in this problem for using normB value from solution. Thanks in advance.
1 Reply Last Post Jun 21, 2010, 12:02 p.m. EDT
Bryan Reed
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Posted: 1 decade ago Jun 21, 2010, 12:02 p.m. EDT

I have a small doubt on using nonlinear characteristics in comsol 4. In materials section while using soft iron, i want to define normB value from solution like mod1.mf.normB. But i am getting error message saying undefined values if try to solve.
I tried to define a constant like 0 or 1 instead of mod1.mf.normB, its working without errors. But it will take linear magnetic characteristics. I am attaching the file here, please check the material contents of the soft iron normB value.
Please help me in this problem for using normB value from solution. Thanks in advance.


I had exactly the same problem and asked tech support for help. It turns out there are a couple of issues with the software that aren't obvious. Try the following:

-Under soft iron's "Basic" material properties (assuming you're using the B = mu*H formalism), define normB to be mf.normB.

-Under the Initial Values in the magnetic field physics, define an initial A field that has a non-zero gradient everywhere; the tech support person put in 1e-6*sqrt(x^2+y^2+z^2) for all three components. This causes it to orange-out the text (complaining that the units aren't right), but apparently this is just a warning, not an error.

Good luck!
[QUOTE] I have a small doubt on using nonlinear characteristics in comsol 4. In materials section while using soft iron, i want to define normB value from solution like mod1.mf.normB. But i am getting error message saying undefined values if try to solve. I tried to define a constant like 0 or 1 instead of mod1.mf.normB, its working without errors. But it will take linear magnetic characteristics. I am attaching the file here, please check the material contents of the soft iron normB value. Please help me in this problem for using normB value from solution. Thanks in advance. [/QUOTE] I had exactly the same problem and asked tech support for help. It turns out there are a couple of issues with the software that aren't obvious. Try the following: -Under soft iron's "Basic" material properties (assuming you're using the B = mu*H formalism), define normB to be mf.normB. -Under the Initial Values in the magnetic field physics, define an initial A field that has a non-zero gradient everywhere; the tech support person put in 1e-6*sqrt(x^2+y^2+z^2) for all three components. This causes it to orange-out the text (complaining that the units aren't right), but apparently this is just a warning, not an error. Good luck!

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