[Getdp] RE: Adaptive mesh refinement with getDP and gmsh

[Christophe Geuzaine]

Jehudi Maes wrote:
> 
> Dear GetDP users,
> 
> I would like to use GetDP and Gmsh for adaptive mesh generation. Included
> you can find my (the part on adaptive mesh generation) original post to Mr.
> Dular and Mr. Geuzaine.
> 
> I would like to thank Mr. Geuzaine for his quick reply. Indeed the main
> problem in the adaptive mesh generation is the generation of the error. I am
> not a specialist in the domain of FE-calculations but from literature I have
> found that for my problem a good error function could be the difference in
> the tangential component of the H or B field calculated from the FE-solution
> and an estimation of this component from an interpolation between an element
> and it's neighbours. However for the construction of the error field I would
> need:
> 
> 1. To get the tangential component of H (or B) from the solution. Is this
> possible in GetDP?
> 2. To access the neighbour values of H and B. Is this possible in GetDP ?
> 3. Possibly (for scaling) also the surfaces of each element.

No, this is not possible for the moment (without some additions to the
source code). Playing only with the .pro files, you may

1) build a simplistic "gradient-based" error estimator 

2) solve dual formulations, which can provide error bounds

I personally use the second approach.

> 
> Kind regards,
> 
> Jehudi Maes
> 
> > -----Original Message-----
> > From: geuzaine at aix10.segi.ulg.ac.be
> > [mailto:geuzaine at aix10.segi.ulg.ac.be]On Behalf Of Christophe Geuzaine
> > Sent: Wednesday, April 25, 2001 7:21 PM
> > To: gmsh at geuz.org
> > Cc: Jehudi.Maes at rug.ac.be; Dular Patrick
> > Subject: Re: [Gmsh] [Fwd: Adaptive mesh refinement with getDP and gmsh]
> >
> >
> > Jehudi Maes wrote:
> > >
> > > Dear Mr. Dular and Mr. Geuzaine,
> > >
> > >  I have been working with GetDP and gmsh for the FE calculations of a
> > > switched reluctance motor (magnetostatic calculations). For these
> > > calculations I have had a lot of help from one of your collegues Johan
> > > Gyselinck. From the websites and the documentation I concluded
> > that it is
> > > possible to use GetDP and gmsh for adaptive mesh generation.
> > Could you be as
> > > kind as to point out how I have to use the combination of GetDP
> > and gmsh for
> > > adaptive mesh generation.
> >
> > For h-type adaptation (i.e. modification of element sizes), you should
> > output a post-processing view which contains the target characteristic
> > lengths. Thus, you should
> >
> > 1) generate a first (coarse) mesh
> > 2) compute target mesh sizes on this mesh, and output the results as a
> >    Gmsh post-processing view
> > 3) load this view in Gmsh, and apply it as the current background mesh
> >    (with 'View->Apply as Background Mesh'), or load the view on the
> >    command line, with the option '-bgm file'
> > 4) re-mesh
> >
> > Step 2) is of course the difficult part, and depends on your problem.
> > GetDP can help to generate the target size view if you have a mean to
> > compute an error field, i.e. some 'volumic' field on the mesh
> > representing (an approximation of) the error. If you can compute such a
> > field, then you can use 'Adapt H1' in a GetDP PostOperation on this
> > field, and you will obtain a valid background mesh for Gmsh.
> >
> > WARNING: if you plan to use background meshes, you need the very latest
> > version (1.18) of Gmsh. This version fixes a serious bug in the
> > generation
> > of adapted 1D meshes.
> >
> > For p-type adaptation (i.e. local modification of interpolation order),
> > you should output an adaptation file, and give it to GetDP on the
> > command line with the '-adapt file' option. The adaptation file can be
> > generated by GetDP by using 'Adapt P1' and by specifying 'Adaptation' in
> > the Format of a PostOperation.
> >
> > >
> > > Kind regards,
> > >
> > > Jehudi
> >
> > I have forwarded your mail to the gmsh mailing list. If you reply to
> > this message, please reply to the mailing list.
> >
> >
> > Christophe
> >
> > --
> > 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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-- 
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


Tel: 32 (0) 4 366 37 10    http://geuz.org
Fax: 32 (0) 4 366 29 10    mailto:Christophe.Geuzaine at ulg.ac.be