[Getdp] Magnetic Force 3

Jasper funkybob at gmail.com
Thu Aug 10 20:19:57 CEST 2006


Thank you for your reply. From what I gather your problem involves
moving charges in a magnetic field, for which the Lorentz force for a
volume can be written as

F = qv x B

>From what I gather this can be rewritten to a form, where for a
magnetostatic problem, the force can be expressed only in terms of the
magnetic field:

f = 1/mu0 * ( B x ( Curl B ) )

My problem (so far) only involves a magnetic field from a permanent
magnet, thus from calculations I only obtain the scalar potential H
(as in the examples on the wiki). From H I obtain B and phi in
post-processing. Now I'm wondering how to obtain F. Thanks for your
reply. I have to look into this some more.

Jasper

On 8/4/06, Kubicek Bernhard <Bernhard.Kubicek at arsenal.ac.at> wrote:
> I calculate a Lorentz Force density in the Postprocessing by the following expression (having a temperature-field-dependent conductivity):
>
> f=jxB=-conducivity(T(x))*grad(V)xCurl(A)=conductivity*Curl(A)xgrad(V)
>
> { Name f ; Value { Term { [ con[{T}]*({Curl a} /\{d v1})] ; In Vol ; Jacobian Vol; } } }
>
> This works in my case.
>
> Maybe this helps you,
> nice greetings from rainy Vienna,
> Bernhard Kubicek
>
>
> -----Ursprüngliche Nachricht-----
> Von: getdp-bounces at geuz.org [mailto:getdp-bounces at geuz.org] Im Auftrag von Jasper
> Gesendet: Donnerstag, 3. August 2006 23:01
> An: getdp at geuz.org
> Betreff: [Getdp] Magnetic Force 3
>
>
> Hi,
>
> I've used a scalar potential to calculate the field in a 3D magnetostatics problem. Looking at the fields the results look correct. Now I would like to calculate the force on a object due to this magnetic field.
> >From what I can gather from the mailing list several people have
> already done this before, but I have yet to find any examples. It appears the force can be calculated in three different ways:
>
> - Take the B-field, and compute 1/mu0 * B x ( Curl B ) over the volume. This is probably easiest achieved in PostProcessing or Gmsh, but somehow the Curl B of my field in Gmsh returns zero...
> - Compute the Maxwell Stress Tensor using the B-field, and integrate it over the surface of the object. This is probably best performed in PostProcessing, but I'm at loss on how to go from the B-field in the element volumes to the field at the surface of the object.
> - Using Virtual Works. No idea how to do that, but it probably involves small displacements :-)
>
> If anybody can show me some examples of computing these quantities it would be very much appreciated. Thanks in advance for your help. Best regards,
>
> Jasper
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