[Gmsh] Transfinite line algorithm
David Colignon
David.Colignon at ulg.ac.be
Wed Jul 29 10:25:28 CEST 2009
Martin Vymazal wrote:
> Dear gmsh users,
>
> I'm trying to generate a second order (P2) unstructured mesh around a
> symmetric airfoil. I managed to create a mesh which is fine so far, but
> I would like to control precisely the number of points on the airfoil.
> To make things a bit more complicated, I'd also like to have more points
> close to the leading and trailing edges of the airfoil. I thought I
> could use the transfinite algorithm with 'progression' or 'bump'
> options, but the progression gives me a bad mesh for a progression ratio
> which is not close to 1.0 (I attached my *.geo files, progression 1.3 at
> the end of the naca0012 geo file already gives strange results.
Hi Martin,
I think displaying the nodes of the 1D mesh on the lines with "shift-alt-p" or Tools->Options->Mesh->Visibility->Nodes
could help you understanding what happens, the way "bump" and "progression" works in Gmsh and what you call "strange"
results (I see what you mean).
http://geuz.org/gmsh/doc/texinfo/gmsh-full.html#SEC45
The optional argument `Using Progression expression' instructs the transfinite algorithm to distribute the nodes
following a geometric progression (Progression 2 meaning for example that each line element in the series will be twice
as long as the preceding one). The optional argument `Using Bump expression' instructs the transfinite algorithm to
distribute the nodes with a refinement at both ends of the line.
and if you search for "bump" in the mailing-list archives, you get this:
http://www.geuz.org/pipermail/gmsh/2008/003526.html
btw , point 5000 is exactly the same as point 381. It is perhaps not a problem but you should avoid it.
Cheers,
Dave
--
David Colignon, Ph.D.
Collaborateur Logistique du F.R.S.-FNRS
CÉCI - Consortium des Équipements de Calcul Intensif
ACE - Applied & Computational Electromagnetics
Institut Montefiore B28
Université de Liège
4000 Liège - BELGIQUE
Tél: +32 (0)4 366 37 32
Fax: +32 (0)4 366 29 10
WWW: http://hpc.montefiore.ulg.ac.be/
Agenda: http://www.google.com/calendar/embed?src=david.colignon%40gmail.com
It seems
> that gmsh calculates the lengths of the lines on the wall of the airfoil
> incorrectly (not precisely enough?). I hoped I could somehow set the
> precision with which the spline representing the wall of the airfoil is
> meshed and thus fix the problem, but found nothing relevant in the
> documentation.
> On the other hand, the 'bump' option seems to have no effect whatever
> value I use (I tried values between 0.5 and 3.5, but I must admit I
> don't know what this number actually means).
>
> I'd appreciate any help/hints or at least an info whether this can be
> done in gmsh or not.
>
> Thank you very much,
>
> Martin Vymazal
>
> ----------------------------------------------------------------
> This message was sent using IMP, the Internet Messaging Program.
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh