# [Getdp] Problem with description of magnetisation

David Colignon David.Colignon at VMESA12.u-3mrs.fr
Wed Oct 3 08:43:04 CEST 2001

```Hi,

for the first question, the solution is

hc [ Region  ] = Vector[ 0 , 0 , 850000 ] ;

Dave

A 17:42 02/10/2001 +0100, vous avez icrit :
>Dear Christophe,
>
>thank you very much for the help.
>Following this, I immediately have three further questions:
>
>1) How can I define hc[] as a vector quantity? I found only scalar
>   constants in the getdp documentation. Did I understand anything
>   wrong?
>
>2) Is a loop of surfaces already a 'forbidden' geometry from a
>   topological point of view?
>
>3) Is it possible to print a function or constant in the
>   postprocessing (for checking purposes)?
>   When I tried this, the program complained, that it was no
>   discrete quantity...
>
>Hope to hear from you soon. :-)
>
>Peter
>
>Patrick Dular wrote:
>>
>> Hi Peter,
>>
>> For this kind of problem (static fields, no source currents), I think
>> the most efficient solution strategy is to use a scalar magnetic
>> potential. You can then compute the magnetization as a post-processing
>> quantity. In the linear case, this formulation is indeed the one given
>> in the demo file of the getdp distribution, i.e.
>>
>> Formulation {
>>   { Name MagSta_phi ; Type FemEquation ;
>>     Quantity {
>>       { Name phi ; Type Local ; NameOfSpace Hgrad_phi ; }
>>     }
>>     Equation {
>>       Galerkin { [ - mu[] * Dof{d phi} , {d phi} ] ;
>>                  In Domain ; Jacobian JVol ; Integration I1 ; }
>>       Galerkin { [ - mu[] * hc[] , {d phi} ] ;
>>                  In Domain_M ; Jacobian JVol ; Integration I1 ; }
>>     }
>>   }
>> }
>>
>> where 'hc[]' is the volume source term (the coercitive magnetic field in
>> your magnets). This formulation is only valid if 'Domain' is
>> topologically trivial (no loops): for its construction, see
>> http://www.geuz.org/getdp/doc/slides/getdp-18.html,
>> http://www.geuz.org/getdp/doc/slides/getdp-25.html (and following), with
>> 'j=0'. If the materials are weakly nonlinear, just write 'mu[{d phi}]'
>> instead of 'mu[]' in the equations, and use an 'IterativeLoop' in the
>> resolution. If the materials are strongly nonlinear, you may want to use
>> a Newton method, which requires the definition of an additional term in
>> the formulation. Tell me if this is the case: I'll show you how to
>> construct it.

Dave

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