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Old   November 12, 2009, 02:40
Arrow Geometry > Netgen > OpenFOAM
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Eric Nutsch
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I am in the process of learning netgen and openfoam.
Due to lack of tutorials, I intend to make one with the help of everyone in this thread.

Here is my plan of attack:

1. Geometry exported as *.igs
2. *.igs loaded into Netgen 4.9.11
3. Netgen Surface Mesh
4. Netgen Volume Mesh
5. Locate and assign patches
6. Set up case files in OpenFOAM 1.6
7. Solve case
8. Export something useful like drag.


I am currently at stage 4. Attempting to mesh the volume will crash Netgen. I attempted geometry healing, but it made the surface skew into many triangles. *.step files did not work either.

The geometry I generated is simple, but non-trivial. An *.igs file is attached to the inside the zip.

Any assistance will be helpful. Thanks guys!
Attached Files
File Type: zip banana.zip (5.1 KB, 52 views)
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Old   November 12, 2009, 03:44
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Philippose Rajan
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Hello Eric,

A Good Day to you!!

Nice to see that you have been trying to use Netgen in combination with OpenFOAM :-)!

I had a look at the banana.igs file.... here are the issues....:

1. Most of the faces in the geometry are wrongly oriented (surface normals are facing inwards). This can be seen in Netgen... faces which are oriented correctly (surface normals pointing outwards) are coloured bright green, whereas the wrongly oriented ones are coloured dark green (As can be seen in the two screenshots - normals_01 and normals_02)

2. The geometry is not closed at the edges around the "banana"... as can be seen in the zoomed in screenshot of that region (holes_01)

In order to get past these issues, you can use the "Heal geometry" option which you are already aware of in Netgen.... I used a tolerance of 0.1, and it successfully sewed the discontinuous edges, and oriented the faces correctly (as shown in screenshot - heal_01)

Once the geometry has been healed, the meshing (both surface and volume mehses) go through without any complaints :-) (As can be seen in screenshot - mesh_01)

Hope this helps you get further :-)!

Have a great day ahead!

Philippose
Attached Images
File Type: jpg normals_01.jpg (6.7 KB, 64 views)
File Type: jpg normals_02.jpg (5.7 KB, 55 views)
File Type: jpg holes_01.jpg (22.8 KB, 60 views)
File Type: jpg heal_01.jpg (35.8 KB, 60 views)
File Type: jpg mesh_01.jpg (70.9 KB, 72 views)
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Old   November 12, 2009, 18:49
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Eric Nutsch
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Thanks for the help Philippose,

Is there any way to design my geometry differently in the beginning to prevent incorrectly oriented faces and un-sewn edges?

I attempted the heal option again with the 0.1 tolerance you recomended. The surface initially looks good then explodes into triangles as soon as the view is rotated(see attached). I thought it might just be a video card thing so i attempted create a surface mesh, but the program errorred and closed.

Thoughts?
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File Type: jpg BananaTriangles.jpg (44.8 KB, 50 views)
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Old   November 13, 2009, 02:53
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Hello again Eric,

Good Morning to you!

Was the screenshot that you attached the result of performing a heal geometry on the same IGE file that you had attached earlier (the one I had worked on)?? Or is it another similar geometry?

Also, which version of Netgen are you working on? The latest binary version from sourceforge (Netgen-4.9.11)?

Since this topic is moving quickly towards an apparent issue with Netgen itself and not to do with OpenFOAM, I would suggest that you post the problems at the Netgen help forum in sourceforge to prevent cluttering up the OpenFOAM forum.

Here is the address to the help forum on Sourceforge:

http://sourceforge.net/projects/netg...s/forum/905307

In order to create the screenshots I uploaded in my previous post, I downloaded the Windows 32-bit binary of Netgen-4.9.11 and healed and meshed the geometry with that.

Have a nice day!

Philippose
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Old   November 13, 2009, 03:09
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Eric Nutsch
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The geometry displayed in triangles is the same exact file you meshed successfully. I am using Netgen-4.9.11 on 32bit windowsXP.

Thoughts?

Thanks again Philippose!
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Old   February 22, 2010, 05:57
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stephane sanchi
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Hi,

I have installed netgen version 4.9.11.

I have 2 questions:

1. In File > Exportfiletype > I don't have OpenFOAM Format ?

2. I have imported an IGES file.
When I do Generate Mesh, I only have the surface mesh, but no volume mesh ! Why ?

Regards,

Stephane.
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Old   February 22, 2010, 06:42
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Hi

You need 4.9-12.svn for Openfoam export.

You cant see the volume mesh in Netgen, but if you export to Openfoam and open with Paraview, create a cut you will see the volume mesh.
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Old   February 22, 2010, 07:44
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Hello there,

A Good Afternoon to you!!

Linnemann is right, the OpenFOAM export function is currently only available in the SVN version of Netgen.... it has not been released as a downloadable binary version yet (I hope to release 4.9.12 sometime soon though :-)!)


As for the volume mesh.... Netgen has always been capable of displaying the volume mesh too.... I guess due to the lack of documentation it remained hidden :-)!

I have attached a screenshot which shows you where you can enable this option....

This dialog box can be found under the menu: "View -> Viewing Options..."


Have a nice day!

Philippose
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File Type: jpg netgen_volume_mesh.jpg (88.8 KB, 74 views)
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Old   February 22, 2010, 07:54
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Aha

Well then I learned something new today as well.

thx Philippose
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Old   February 22, 2010, 08:39
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stephane sanchi
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Hi,

I have problems installing netgen version 4.9.11-svn.

Where can I set the path for Tck and Tk ?

[120]cfs10-sanchi /home/sanchi/mynetgen/netgen % ./configure
checking for a BSD-compatible install... /usr/bin/X11/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking for correct TEA configuration... ok (TEA 3.6)
checking for Tcl configuration... configure: WARNING: Can't find Tcl configuration definitions

Stephane
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