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Model BH-curves with remanent flux density at H=0

Posted Feb 25, 2014, 5:37 a.m. EST Low-Frequency Electromagnetics, Materials 4 Replies

Florian Oberhauser
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Hello,
I make some studies to determine the magnetic properties of metals and have to take in account a small remanent magntic flux density B.
I defined a sample material with a known BH-curve and at H=0 I set a small value for B to set the remanent flux density..
But I always get the error no solution found even with minimum step size.

Is there a other possibilits to simulate nonlinear materials with a small remanent flux density?

Thanks for your advices.
4 Replies Last Post Feb 28, 2014, 4:56 a.m. EST
Jens Krause
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Posted: 1 decade ago Feb 26, 2014, 10:02 a.m. EST
Hallo Florian,

you have to remember that H and B are really vector quantities. If you simply shift
the BH curve there is no direction defined. I assume that you use

Hnorm = f(Bnorm) + Bremenace

But in which direction is the remance pointing. I guess that is why you
system is not well defined and Comsol is complaining

Regards

Jens
Hallo Florian, you have to remember that H and B are really vector quantities. If you simply shift the BH curve there is no direction defined. I assume that you use Hnorm = f(Bnorm) + Bremenace But in which direction is the remance pointing. I guess that is why you system is not well defined and Comsol is complaining Regards Jens
Florian Oberhauser
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Posted: 1 decade ago Feb 26, 2014, 1:53 p.m. EST
@Jens
Thanks for the advice,

I have done it as you said (Hnorm = f(Bnorm) + Bremenace) and I pointed out that this is the problem,but I do not find another possibility to combine nonlinear material and remanent flux density for a given direction.

Regards
Florian
@Jens Thanks for the advice, I have done it as you said (Hnorm = f(Bnorm) + Bremenace) and I pointed out that this is the problem,but I do not find another possibility to combine nonlinear material and remanent flux density for a given direction. Regards Florian
Jens Krause
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Posted: 1 decade ago Feb 27, 2014, 2:07 a.m. EST
One idea:

in Ampere's law -> Magnetic field you can change the constitutive relation to Magnetisation.
The you can enter a vector. e.g.

Mx = M0x + fx(Bx,By,Bz)
My = fy(Bx,By,Bz)
Mz = fz(Bx,By,Bz)

which would be for permeant magnetisation in x-direction. The functions fx,fy,fz rerpesent
a vectorial M(B) relation. For isotropic material this could be
fx=F(normB)/normB*Bx and y,z accordingly

F now is a function with F(0)=0 representing a scalar M(B) law..

A bit of a work to implement, but should do the job.

Good luck,

Jens
One idea: in Ampere's law -> Magnetic field you can change the constitutive relation to Magnetisation. The you can enter a vector. e.g. Mx = M0x + fx(Bx,By,Bz) My = fy(Bx,By,Bz) Mz = fz(Bx,By,Bz) which would be for permeant magnetisation in x-direction. The functions fx,fy,fz rerpesent a vectorial M(B) relation. For isotropic material this could be fx=F(normB)/normB*Bx and y,z accordingly F now is a function with F(0)=0 representing a scalar M(B) law.. A bit of a work to implement, but should do the job. Good luck, Jens
Florian Oberhauser
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Posted: 1 decade ago Feb 28, 2014, 4:56 a.m. EST
@Jens

Thanks this is a good idea with your advice I could solve it nearly the same way.

Solution:

-I had a BH-curve for my material and converted it into a curve murB (mur = f(B)).

-In the ampere's Law node for the material I chose "Remanent Flux Density (B =mu0*mur*H+Br)"

-For relative permeability I chose "User defined" and "Isotropic".

- The function I inserted was "f(mf.normB[1/T])". The function must depend on B , if it depends on H you have a circulary dependency error.

-The remanent flux density was set to some value in x-direction.

Now I think it is working.

Thanks for the help and maybe my solution can be helpful for others.

Florian
@Jens Thanks this is a good idea with your advice I could solve it nearly the same way. Solution: -I had a BH-curve for my material and converted it into a curve murB (mur = f(B)). -In the ampere's Law node for the material I chose "Remanent Flux Density (B =mu0*mur*H+Br)" -For relative permeability I chose "User defined" and "Isotropic". - The function I inserted was "f(mf.normB[1/T])". The function must depend on B , if it depends on H you have a circulary dependency error. -The remanent flux density was set to some value in x-direction. Now I think it is working. Thanks for the help and maybe my solution can be helpful for others. Florian

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