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Creating a region with a constant gradient field

Posted 18 feb 2013, 08:54 GMT-5 Low-Frequency Electromagnetics Version 4.3a 4 Replies

Chris Nadovich
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I want to create a region of air with a static magnetic field in the z direction that has a constant slope (gradient) in that direction as well, for example H(x,y,z)=(0,0,1+z/10). Once I have this, I'm planning to put an object in it, but thus far I've not figured out to to make this sort of initial field. I tried creating a cube with the H field on the boundaries set to 0,0,1+z/10, but the calculated result within the cube wobbles away. It's even different along the boundaries! Very puzzling.

4 Replies Last Post 4 mar 2014, 05:28 GMT-5
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 25 feb 2013, 15:12 GMT-5
Hi

How to define a static field depends on the physics module, in MFNC (magnetic field No current) it's enough, in 2D, to define the potentials Vm, but in the other MF... you need to define the full vector field A.

But what really puzzles me, and that took some time for me to find out how to answer, is your demand for a field
H=(0,0,1+z/10)

For me that is not "physical", the simplest way is probably to say as it violates "div B = 0" that is a known mathematical property for a correctly define B linked to a vector magnetic potential A defined by "rot A = B"
so even f you have some magnetisation M I'm not sure you can get your H field like that, as H = 1/mu0*B+M while
M = 0 for air/vacuum

--
Good luck
Ivar
Hi How to define a static field depends on the physics module, in MFNC (magnetic field No current) it's enough, in 2D, to define the potentials Vm, but in the other MF... you need to define the full vector field A. But what really puzzles me, and that took some time for me to find out how to answer, is your demand for a field H=(0,0,1+z/10) For me that is not "physical", the simplest way is probably to say as it violates "div B = 0" that is a known mathematical property for a correctly define B linked to a vector magnetic potential A defined by "rot A = B" so even f you have some magnetisation M I'm not sure you can get your H field like that, as H = 1/mu0*B+M while M = 0 for air/vacuum -- Good luck Ivar
Edgar Kaiser
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Posted: 1 decade ago 25 feb 2013, 17:23 GMT-5
Hi Ivar,

I am impressed. I admit, I tried to define the 'constant gradient' field and I failed like the initial poster did. You showed the way to look at things, to look at the physics.
J.C. Maxwell would probably have a lot of fun with COMSOL.

Cheers
Edgar

Hi Ivar, I am impressed. I admit, I tried to define the 'constant gradient' field and I failed like the initial poster did. You showed the way to look at things, to look at the physics. J.C. Maxwell would probably have a lot of fun with COMSOL. Cheers Edgar
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 26 feb 2013, 01:31 GMT-5
Hi Edgar

I'm sure most physicist, discovering COMSOL, would have as much fun, really doing physics again

--
Have fun COMSOLing :)
Ivar

Another example the two simple models below, how easy they are to set-up and how much more they tell us about D and M, and what they look like, compared to when we had to write out the equations and sketch what we believed were the results ;)
Hi Edgar I'm sure most physicist, discovering COMSOL, would have as much fun, really doing physics again -- Have fun COMSOLing :) Ivar Another example the two simple models below, how easy they are to set-up and how much more they tell us about D and M, and what they look like, compared to when we had to write out the equations and sketch what we believed were the results ;)
Janmejaya Tripathy
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Posted: 1 decade ago 4 mar 2014, 05:28 GMT-5
Hi
I am using 4.3b and trying for particle tracing based on gradient of magnetic field, but in 3d the gradient of magnetic field returns zero result and if from the pde of mathematical module I am getting the gradient and putting them in the force equation then the particles are not responding it. Please help regarding this.
Thanks
Hi I am using 4.3b and trying for particle tracing based on gradient of magnetic field, but in 3d the gradient of magnetic field returns zero result and if from the pde of mathematical module I am getting the gradient and putting them in the force equation then the particles are not responding it. Please help regarding this. Thanks

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