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Old   October 9, 2004, 03:42
Default Meshing???
  #1
Kiran
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Hi, I'm trying to import a model created in Pro/E into gambit, but I'm not sure what preferences to give while importing a *.stp model.The model is one which is hollow inside, and I'm not sure how to mesh the hollow part.Can anyone pls help me? Thanks in advance, -Kiran
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Old   October 9, 2004, 06:13
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  #2
SAM
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try to repeat the gambit tutorials and also read teh gambit modeling guide and users guide

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Old   October 11, 2004, 08:48
Default Re: Meshing???
  #3
Jason
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From the sound of it, you are trying to import the physical geometry. I recommend creating the control volume in Pro/E (i.e. the volume around the airplane instead of the airplane, or the volume inside of the pipe instead of the pipe). There is issues with taking complex geometry (sweeps and smooth blends seem to be the biggest problems) from Pro/E to Gambit that tend to make boolean operations and split operations not always work. After a few months of wasting time with trying to setup geometry in Gambit, I just started doing all of the geometry setup in Pro/E, so all I have to do is connect any volumes I want connected, clean up the geometry (merging faces and edges), and then mesh.

As for the options to be set, I recommend leaving the default options, which is only the "Make Tolerant" option on. The "Heal Geometry" option hasn't made any of my Pro/E geometry easier to work with and it can take up a lot of time if the model is complex, so I stopped bothering with it.

As far as helping you with meshing, then you need to be a little more descriptive with your case. I don't understand your description of your geometry, and you don't explain what you're trying to get out of it. If you can give a better description of what you're geometry is and what you're trying to get out of the solution, then I may be able to help you better (but no promises )

Hope this helps, Jason
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Old   October 11, 2004, 10:18
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  #4
SAM
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but wont this also makes the problems

as every body knows whil importing geomety from pro E to gambit there is loss of data

so there will be again problems when we import the complete domain from the pro E and will take more time to clean up the dirty goemetry with more surface, volumes

wat u think

thins are not so easy
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Old   October 11, 2004, 10:18
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  #5
SAM
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but wont this also makes the problems

as every body knows whil importing geomety from pro E to gambit there is loss of data

so there will be again problems when we import the complete domain from the pro E and will take more time to clean up the dirty goemetry with more surface, volumes

wat u think

things are not so easy
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Old   October 12, 2004, 01:26
Default Re: Meshing???
  #6
Kiran
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First of all thanks for the help so far, guys.Coming to the geometry, I'm trying to analyze the hypersonic flow inside a rocket nozzle.I tried to create the geometry in Gambit, but I couldn't generate a non-uniform grid for creating vertices.I tried to curve fit the data points, but the equation wasn't convincing.So, I figured the easiest way was to create the geometry in Pro/E and export the model.But I'm having problems when I try to import as this is the first time I'm trying to export a Pro/E model to Gambit.I'm not sure what options to select.Also, I don't know whether to export surfaces/wireframes/shells/solids.....Can u help me? Thanks, Kiran
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Old   October 12, 2004, 04:41
Default Re: Meshing???
  #7
SAM
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by any means u have to work in gambit to clean the goemety.

i use to prefer in IGES format and work on it

here i am pasting some sentences and reference jsut check it (if u give me ur yahoo id i will send u this paper)

ACCESSING CAD GEOMETRY FOR MESH GENERATION Mark W. Beall1, Joe Walsh2, Mark S. Shephard3 1Simmetrix Inc., Clifton Park, NY., U.S.A. mbeall@simmetrix.com 1Simmetrix Inc., Clarkesville, GA., U.S.A. jwalshl@simmetrix.com 3Rensselaer Polytechnic Institute, Troy, NY., U.S.A. shephard@scorec.rpi.edu

CAD systems often use relatively large tolerances on an entity-by-entity basis to provide robustness to model operations. This approach is referred to as variable tolerances or tolerant modeling by different CAD systems. The use of these large variable tolerances produces gaps and overlaps in the geometry and topology of the CAD system B-Rep model as illustrated in the simple (and extreme) example in Figure 1.
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Old   October 12, 2004, 06:29
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  #8
Kiran
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Thanks for ur response.In case u're talkting about decreasing the tolerances, I've already done that in Pro/E.I've set the tolerances to 10e-6.I hope thats enough to decrease the gaps in geometry.Anyways,I'd appreciate if you could send me the paper u r talking about.My ID is "kkgona@uncc.edu".Meanwhile, can u give me an idea as to wat to export (surfaces/shells/solids/wireframes etc..) while trying to export models from Pro/E? Thanks again for ur help, Kiran
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Old   October 12, 2004, 08:33
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  #9
Jason
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Things are never easy

The first step is to make sure your control volume is simple geometry (frustrum, cone, hemisphere, sphere, cylinder, rectangle, etc.). When you subtract the geometry from the control volume, check to make sure that there aren't any gaps. The subtract function in Pro/E will take care of overlays, which can be just as much of a problem when you import to Gambit.

The next step is to lower your accuracy, like Kiran did. I recommend enabling absolute accuracy, but if it's a large part or it's an assembly, this won't always work. In those cases, just drop the accuracy as low as possible.

Export the geometry (solids) as a step.

When you import the step make sure the "Make Tolerant" option is on. The geometry that was the problem to begin with will still need to be cleaned up, but the rest of the control volume will not have to be. With some complex models, this has been the only way I could get a control volume, and with some not-so-comlpex geometry, this has saved a lot of time instead of trying to get the geometry to subtract from a control volume (which can be a headache in Gambit... even the Fluent guys aren't sure what most of those ACIS errors are). I've even had better luck with being able to split the control volume or even cutting from or adding to it when I use this method.

It's not a perfect method, I'll admit that, but it can be a huge time saver, especially if you're dealing with assemblies, and I've never had problems with having to clean up the control volume. I'm sure everyone would agree that the most accurate is to create the geometry in Gambit to avoid error, but that's not always possible. This is the way I've found to save time without sacrificing the accuracy of the part any more then I have to.

Thanks, Jason
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Old   October 16, 2004, 03:39
Default Re: Meshing???
  #10
SAM
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export in the form of solid and simplify the geometry to a form which is needed for cfd analysis

regards

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Old   October 21, 2004, 20:18
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  #11
Chetan Kadakia
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Kiran, did the methods work for you?
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Old   October 22, 2004, 05:29
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  #12
SAM
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Kiran did u get that paper which i sent u

regards
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Old   October 23, 2004, 00:53
Default Re: Meshing???
  #13
Kiran
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Yes...after I decreased the tolerances to 10e-6 they did work.I had to clean the geametry a bit before I meshed it.
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Old   October 23, 2004, 00:55
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  #14
Kiran
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No I did not get the papers yet.Can u pls send me another e-mail? thanx, Kiran
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Old   October 31, 2004, 10:59
Default Re: Meshing???
  #15
mohammed ali
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hi kiran, even iam working on a hypersonic flow in the inlet of a scramjet engine.i too am finding it difficult to mesh the hollow portion inside the inlet. could u (or anybody who is reading this,in case u know it)please tell me how to do the meshing of the internal portion of the inlet. thanking u in advance as well as the outer portion ali
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Old   November 1, 2004, 09:15
Default Re: Meshing???
  #16
Jason
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I highly recommend splitting the volume so that there is actually two volumes... the inside of the inlet, and the external control volume. When you split the volume, make sure the "connected" option is selected. This way, the two volumes "share" that face. With the two faces connected, both volumes share the mesh on that face, and unless you define it as some boundary condition, Gambit won't export the face when you create the mesh, it just becomes construction geometry.

Hope this helps.

Jason
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Old   November 4, 2004, 04:03
Default Re: Meshing???
  #17
Kiran
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Hi ali, It depends on whether you're doing a 2-D version or 3-D version.If you're doing a 2-D axisymmetric model, then it shouldn't be a problem.But if you're working on a 3-D model, then I think u'll have to split the volumes as Jason said and then try to merge the volumes separately. good luck, -kiran
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