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 <[email protected]>:
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
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