[Gmsh] Cyclic boundary condition (same mesh when extruding a surface ?)

Durufle marc marc_durufle at yahoo.fr
Fri Jun 18 10:41:27 CEST 2010

I want to mesh a part of a 3-D domain (which is cyclic), and impose cyclic boundary conditions, but the problem is that in my solver I assume that the two surfaces of the 3-D cell are the same. I send you an exemple of a part of a sphere. And by following recommendations of a previous message :
I didn't get the same mesh when I extruded the surface by rotation.
So, is there a solution to have the same surface mesh for the two surfaces ? (teta = 0 and teta = pi/4) 
In the given example (for a periodic mesh), surfaces of the cube didn't have the same mesh actually :(

Thanks for your help.

De : "gmsh-request at ace20.montefiore.ulg.ac.be" <gmsh-request at ace20.montefiore.ulg.ac.be>
À : gmsh at geuz.org
Envoyé le : Jeu 17 juin 2010, 18h 35min 49s
Objet : gmsh Digest, Vol 89, Issue 19

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Today's Topics:

   1. Help (Henri Pascal-Jenny)
   2. Question about reclassify (Martin Vymazal)
   3. Re: freefem (Luis Casillas)


Message: 1
Date: Thu, 17 Jun 2010 11:26:36 +0200
From: "Henri Pascal-Jenny" <henri.pascal-jenny at sogeti.com>
Subject: [Gmsh] Help
To: <gmsh at geuz.org>
Message-ID: <00e801cb0dff$31b3f550$1c7de20a at so.fr.ad.sotranet.net>
Content-Type: text/plain; charset="us-ascii"


I am facing the  problem of finding the minimum-3D box enclosing AS CLOSE AS
POSSIBLE a set of 3D mesh points . 

I would like to avoid the use of a too-sophisticated algorithm .

(cf.  http://en.wikipedia.org/wiki/Minimum_bounding_box_algorithms)

Actually, when used straightforwardly, the method "BoundingBox"  available
in a  gmesh-session returns a  3D box  

which box does not always correspond to the minimum volume enclosing the set
of points 

( imagine a thin and not fully-planar shape tilted in respect to the axes of
a standard coordinates-frame )

In fact, the matter comes from the bulk orientation of the envelop of the
set of points under consideration.

The usage is : 

BoundingBox { expression, expression, expression, expression, expression,
expression };

what forces the bounding box of the scene to the given expressions (X min, X

Y min, Y max, Z min, Z max).

Therefore, I am wandering if there is a way of  operating the "BoundingBox"
method in order to get in the end the  truly-minimum 3D box enclosing. 

Actually, I guess that there is a preliminary thing to do related to the
coordinates system ; maybe I am wrong.

Well, I would appreciate it very much if anyone could supply me for any
piece of information regarding my problem. 

Thanks a lot in advance for your attention and your cooperation.


Henri Pascal-Jenny 

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Message: 2
Date: Thu, 17 Jun 2010 17:37:03 +0200
From: Martin Vymazal <martin.vymazal at vki.ac.be>
Subject: [Gmsh] Question about reclassify
To: gmsh at geuz.org
Message-ID: <20100617173703.14972p7a6eirqrkv at horde.vki.ac.be>
Content-Type: text/plain; charset=ISO-8859-1; DelSp="Yes";


  I would like to ask if it is possible to launch the 'reclassify'  
command from command line. I normally use it from the gui, but since  
all the other mesh processing is done using scripts, it would be nice  
if I could do this also without opening the gui.

I have one more little question. Suppose I run reclassify, I get a lot  
of surfaces and I hide some of them by clicking in the gui. Is it  
possible to create a new geo/msh file which contains only entities  
currently set as visible? What I mean is that I don't want to save a  
file which is the original mesh with additional info about visibility,  
but I'd like to have a new file in which the 'invisible' parts are  
completely absent.

  Thank you.

  Best regards,

  Martin Vymazal

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Message: 3
Date: Thu, 17 Jun 2010 09:41:22 -0600
From: Luis Casillas <casillasluis at lanl.gov>
Subject: Re: [Gmsh] freefem
To: gmsh at geuz.org
Message-ID: <8FA18878-46E8-4817-B926-BBD404D49B94 at lanl.gov>
Content-Type: text/plain; charset="us-ascii"; Format="flowed"

I continue with the attempt to export a mesh to freefempp,
the strange thing is that I have had success in a few cases,
but in most of them I get errors, I'm attaching a pair of meshes that
don't work,


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