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Old   March 17, 2007, 17:44
Default MSH Import
  #1
Vivek Vasudevan
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Hi folks,

I have a *.msh file created in TGrid 4.0.16 that I need to reflect. While Tgrid allows me to view a reflection, it does not allow me to manipulte / cnange the reflected entity. So what I see is merely a reflection.

I know Gambit allows for manipulation of reflected meshes / geometries, but it simlpy takes ages to import a MSH file into Gambit. I contacted another user at CFD-online who faced the same problem abut a year ago, but he could never resolve it. I'd appreciate any help / feedback forthcoming from the forum uers to overcome my predicament. Investing in a new software simply for a reflection seems too prepostrous an investment to make! And any way, there's no guarantee that the new vendor would be any more forthcoming than Fluent in providing timely tech support or pointing out inefficiencies in their products before hand!

Is there ANY other software / pre-processor that would allow me to import a MSH file and give me a workable reflection?" Also, though very unlikely, is it possible to achieve a reflection by way of rotations and translations of the mesh/geometry?

Thanks and regards, Vivek
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Old   March 19, 2007, 05:34
Default Re: MSH Import
  #2
Razvan
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Yes, this is true, not including a simple operation like copying mesh through reflection can be viewed as an unforgivable mistake, especially when dealing with such a widely-used software like TGrid. But you must also consider that TGrid was not created to replace Gambit, it is not a true preprocessor, for not having geometric functions absolutely necessary for such a program. It can only operate starting from an existent boundary or volume mesh, and that proves it is a highly specialised tool, aimed at specific users in specific environments.

Personally, I never found a better Boundary-Layer mesher than TGrid, and I prefer TGrid over most unstructured meshers. The quality of its grid is comparable only to ANSA, in my opinion.

I do not agree to this: "it simlpy takes ages to import a MSH file into Gambit". I just tested this with a 520,000 elements mesh, and with the timer in my hand, the whole process took only 39 seconds!!! (on my dual Opteron 280, 8GB RAM workstation, but only one core and around 650MB of RAM are actually used)! If you cannot wait that long, then what can I say...

So clearly, having Gambit, your problem is solved. Maybe you are not performing the import operation correctly. Carefully review your steps and try again, it cannot take ages, unless you are importing a mesh that does not fit into your current RAM memory!

All the best, Razvan
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Old   March 19, 2007, 06:50
Default Re: MSH Import
  #3
Vivek Vasudevan
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Thanks Razvan.

Probably Im not doing something correctly while importing the MSH file into Gambit.

What feature angle did you use to import into Gambit? I tried a variety of feature angles and I got responses varying from "Unable to form topology" to FATAL ERROR to well, "session time out" after 8 hours!

I have the 3D boundary mesh imported from a 3D imaging software and use TGrid to generate an unstructured tet volume mesh in the enclosed surface mesh. I need to use reflect option and connect the reflections to impose a periodic boundary condition on opposing walls to mimic an infinitely repeating unit cell.

I'll reconfirm the server configuration and get back to you.

Thanks once again, Vivek
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Old   March 19, 2007, 20:09
Default Re: MSH Import
  #4
Vivek Vasudevan
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Hi folk,

Like I said, buying a software simply to reflect a geometry seems like a prepostrous idea. Apparently, ICEM CFD can do what Im out to achieve, but costs about 6000 USD for a one-year license - which I doubt my supervisor will be pleased to spend just for reflecting an entity!

Anyway, I managed to export the volume mesh created in TGrid as a PATRAN *.neu file, which I could read into CFX5Pre (The pre-processor with CFX 5). I was then able to reflect the mesh. However, I could not find any option within CFX Pre that would allow me to export the mesh back into TGrid.

Could someone advise how do I export from CFX Pre to TGrid?

Thanks, Vivek
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Old   March 20, 2007, 02:48
Default Re: MSH Import
  #5
Razvan
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Most frequently I use feature_angle=100deg. Generally, a lower value of this parameter should result in a lower number of boundary edges, more continuous boundary faces with less or no internal (dangling) edges.

8 hours is a really long time... Something is definitely wrong, either in the exported file or in the import procedure you use. For example, I hope that when you export the file from TGrid, you are not actually using "Export" command. If yes, than you should just "Write" the mesh. And at import, you should use "Import\Mesh\TGrid,3D,feature_angle=100(or less)". That should do it.

All the best, Razvan
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Old   March 20, 2007, 07:57
Default Re: MSH Import
  #6
Vivek Vasudevan
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Hi Razvan,

I went through my surface mesh generation steps but couldnt find anything out of place. I save the mesh in TGrid using "write" and import it into Gambit exactly as you have mentioned. I have tried feature angles right from 0 to 135 (default) resulting in either insufficient data for Gambit to reconstruct the topology, or in a FATAL ERROR, or an eternity to load resulting in a 'session time out'.

Interestingly, I had created another surface mesh a couple of months back and had successfully been able to import it into Gambit after much trial and error then. Thi current surface mesh is created similarly, but seems unable to be read by Gambit.

Could I send you my 3D surface mesh file (~ 3 MB) for you to try importing into Gambit at your end ?

Appreciate your timely responses, Vivek
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Old   March 30, 2007, 10:53
Default Re: MSH Import
  #7
giofer
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There will be a new software on the market that works similar to ICEM CFD, works with nurbs and allow reflection of geometryboth with mesh. Take a look at www.go-mesh.it
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