[Gmsh] Transfinite line algorithm

[Martin Vymazal]

Hello Dave,

  thank you very much for your reply. I had an idea how 'progression'  
works, the problem is that this is not what I see in my mesh when I  
visualize the nodes on the wall of the airfoil. As I wrote in my  
previous email, making progression slightly bigger than 1.0 (say, 1.3  
or bigger), gmsh gives me a completely incorrect mesh. Sometimes it  
even tries to mesh the inside of the airfoil.
  I also found the question/reply about 'bump' in gmsh mailing list  
archives to which you pointed me, but it does not help me to  
understand whether I'm doing something wrong or if gmsh simply cannot  
mesh the airfoil the way I want. My only question is simply: can I  
control the number and distribution of the mesh points on the airfoil  
in the geo file I attached yesterday? If so, how?
  Once again, thanks for any help.

  Best,

    Martin Vymazal



Cituji David Colignon <David.Colignon at ulg.ac.be>:

>
> 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
>
>



----------------------------------------------------------------
This message was sent using IMP, the Internet Messaging Program.