[Getdp] Problem with description of magnetisation

[Peter Fouquet]

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.
> 
> Christophe
> 
> pf231 at cam.ac.uk wrote:
> >
> > Dear all,
> >
> > Thank you, first of all, to Christophe and Patrick for the brilliant
> > getdp program.
> >
> > I am presently working on a 3D FEM simulation of the transition region
> > from a permanent magnetic hexapole field to a dipole field. Being no
> > expert in FEM simulations at all I find myself in a problem, where I
> > need some help, which I hope you can provide me with:
> >
> > I want to describe the system in a vector potential approach with the
> > edge finite elements with the tree gauging, that you sketched in the
> > manual. The problem comes in, when I try to describe the magnetisation.
> >
> > Which function space can I use for it? A vector field didn?t work,
> > because I couldn?t define a curl on it (curl (magnetisation)=0), but
> > otherwise I don?t know how to get it into the Galerkin equation (if I
> > use it as a constant) or to define it properly (if I use a 1form space
> > for the magnetisation).
> >
> > If you could give me a direction to solve the problem, I would be
> > extremely grateful to you.
> >
> > Thank you very much in advance, best regards
> >
> > Peter Fouquet
> >
> > _______________________________________________
> > GetDP mailing list
> > GetDP at geuz.org
> > http://www.geuz.org/mailman/listinfo/getdp
> 
> --
> Christophe Geuzaine
> 
> Tel: 32 (0) 4 366 37 10    http://geuz.org
> Fax: 32 (0) 4 366 29 10    mailto:Christophe.Geuzaine at ulg.ac.be
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