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Frustrated GAMBIT user in need

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Old   August 1, 2007, 08:28
Default Frustrated GAMBIT user in need
  #1
David Banks
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Im pulling my hair out here trying to import geometry into GAMBIT from software i am exporting from.

I can save my model under extensions, ".stl", ".bas" and ".obj".

Can i import these into FLUENT? My version of FLUENT can import the following files;

ACIS, Parasolid, IGES, STEP, CATIA V4/V5, ICEM Input, Vertex Data, CAD, Mesh (in the form of .msh), Turbo and Plug-In.

Somebody help please!

Regards, Dave
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Old   August 1, 2007, 17:17
Default Re: Frustrated GAMBIT user in need
  #2
red lemon
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TGrid can import the .stl file. THen write out as a mesh file and import this into Gambit using Import>Fluent Mesh to create a faceted geometry.
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Old   August 2, 2007, 05:38
Default Re: Frustrated GAMBIT user in need
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David Banks
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Thankyou

I have tried that but it gives me the following message;

Error: The Fidap Neutral file header (record 1) is non-standard Error: Error encountered while reading the header info. Make sure correct mesh dimension and type have been supplied. Gambit is unable to Support "file".

Does this mean i need to alter my mesh parameters in TGrid?

D
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Old   August 2, 2007, 11:36
Default Re: Frustrated GAMBIT user in need
  #4
lee
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I think you need to save your model in the format .stp, .stl and .obj. Not the extensions.

First of all your CAD software must have capability to export file in these formats.
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Old   August 2, 2007, 13:40
Default Re: Frustrated GAMBIT user in need
  #5
Allan Walsh
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I'm confused - are you trying to import files into FLUENT as you stated? or Gambit?

You have probably gone through this many times, but just to reiterate: You are creating, or will create, your geometry in some CAD program and then are saving it as an ACIS file (*.stl). It would appear that you don't have the option to save it as an IGES file (*.igs) another common graphical format.

Now you import the ACIS file into Gambit. There are several options here about healing geometry etc. Can you do this? Does it show you anything on the Gambit screen? By the way, my experience in importing ACIS files created with AutoCAD was that it still took quite a bit of work to clean up the geometry to be meshed. IGES files worked too but sometimes you just end up with vertices.

Once you make your mesh, export it, and then read that into Fluent.

I'm sure there are lots of other procedures but my experience is that the one described above is the most straight forward. Which step are you getting hung up on?
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Old   August 3, 2007, 04:41
Default Re: Frustrated GAMBIT user in need
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David Banks
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Let me clear up the confusion (my fault), I am trying to import the file into GAMBIT.

I have created an STL file which I have tried to import through IMPORT>MESH>STL. The problem I am experiencing is that the import seems to stall at the 90% mark during 'Reading Connectivity'. Do you suggest this may be something to do with the number of elements/nodes my model has?

Its frustrating because I have this perfect, high resolution shape which FLUENT happily reads...its just that, at the moment, it is useless because there are no boundary regions defined on it.

I feel i am almost there, i just need a bit more guidance regarding the best way to upload the STL file. I have the Shape as a NASTRAN file as well if that helps?

Cheers

Dave
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Old   August 3, 2007, 13:55
Default Re: Frustrated GAMBIT user in need
  #7
Allan Walsh
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Ok, so when you try and import the *.stl file it stalls at the 90% mark. What happens in Gambit? Do you see any geometry on the Gambit screen?

What happens if you just IMPORT>ACIS?

If you don't have anything in GAMBIT, you won't be able to make a mesh to for FLUENT.

Have you tried importing your Shape into Fluent in the NASTRAN format?
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Old   August 6, 2007, 06:00
Default Re: Frustrated GAMBIT user in need
  #8
David Banks
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I have successfully imported a smaller STL file and i can see the geometry on the screen. The seabed bathymetric shape i imported is made up from several faces stitched together and wrapped with 5 other flat faces to create a volume representing my 'sea'.

I already have face meshes and need to mesh the volume now but keep getting the same message;

"Initialisation failed; perturb boundary nodes and try again:

Error: TG_MESH_DOMAIN failed with error code 1

Error: Tetrahedral meshing has failed for volume v_volume.1 This is usually caused by a problem in the face meshes. Check the skewness of your face meshes and make sure the face mesh sizes are not too large in areas of small gaps"

Does this mean the mesh is not coarse enough in certain faces? Can this be easily fixed?

Cheers

Dave
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Old   August 6, 2007, 13:19
Default Re: Frustrated GAMBIT user in need
  #9
Allan Walsh
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Usually it can be fixed fairly easily with one of two options. The first would be to look at the faces where it has failed and try smoothing the mesh. Second, sometimes you can mesh the faces with a different scheme and then get the volume to mesh up. When the volume mesh fails, sometimes I have had success by making the face meshes finer and sometimes making them coarser. And, sometimes, meshing the faces prior to meshing the volume works.

My experience is that Gambit 2.3 is more robust than 2.2.

Prior to meshing, you should use the geometry clean-up tool (the little hand and mop icon) to check for gaps, sharp corners, duplicate geometry etc. It can take a bit of playing around.

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Old   August 7, 2007, 16:02
Default Re: Frustrated GAMBIT user in need
  #10
red lemon
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use gambit 2.4.6 now released
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