help with GetDP needed

[Christophe Geuzaine]

Samuel Kvasnica wrote:
> 
> Hi Christophe,
> 
> I was bothering you some time ago with questions about GetDP. Now I succeeded in doing
> plasma simulations where magnetic field computed by GetDP is used. Well, qualitatively
> everything looks good, but I'm not able to refine my results since the results from GetDP
> are quite noisy and in a strange way, even with DivB!=0 at some places where B changes rapidly
> and this causes numerical heating in my simulations. I don't know if that's a problem of the solver or of the
> interpolation during postprocessing using OnPlane or OnLine method. I'm sending you
> as an attachment a typical picture of z component of B. Mesh size was cca 1 unit on x axis.
> Could you give me an advice please ?
> 

OK, this is not surprising, due to the representation of the potential
'a' with first order classical nodal elements. The exterior derivative
of the potential (-> b) is discontinuous, even if the conservation of
its normal derivative is assured. You can very simply use second order
interpolation, by adding a set of basis functions in your FunctionSpace.
For example, for the 2D vector potential, you could define :

FunctionSpace {
  { Name Hcurl_a_MagSta_2D; Type Form1P;
    BasisFunction {
      { Name se; NameOfCoef ae; Function BF_PerpendicularEdge; Support
Vol_Tot; 
        Entity NodesOf[All]; } // these are the 1st order elements
      { Name se2; NameOfCoef ae2; Function HBF_PerpendicularEdge_2E;
Support Vol_Tot; 
        Entity EdgesOf[All]; } // these are the additional hierarchical
basis functions
    }
    Constraint {
      { Type Assign; NameOfCoef ae;  Entity NodesOf UsingConstraint
MagVectPot_2D ; }
      { Type Assign; NameOfCoef ae2;  Entity EdgesOf UsingConstraint
MagVectPot_2D ; } 
         // the constraint for the hierarchical basis functions applies
to edges
    }
  }
}

The names of the new basis functions refer to Hierarchical Basis
Functions (HBF), associated with edges, and of degree 2 (2E).

Good luck,

-- 
Christophe Geuzaine

Tel: +32-(0)4-366.37.10    mailto:Christophe.Geuzaine at ulg.ac.be
Fax: +32-(0)4-366.29.10    http://www.montefiore.ulg.ac.be/~geuzaine/