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[GAMBIT] Problem with merging edges/faces

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Old   June 11, 2012, 11:49
Default Problem with merging edges/faces
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Hello everybody,

I have a problem while importing geometry from Solid Works to Gambit.
As showed in figures, there are 3 blades that would be meshed. But every side edges of blades has broken in two edges while there are circles in leading edge and trailing edges.
So when I mesh the airfoil it wouldn't get a smooth mesh because of difference in scale of edges. I tried to merge them but while the geometry is complex, it could not create a real face/edge.
Is there any idea to resolve this problem?

Thank you in advance,
bahar
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File Type: png 3d.png (79.5 KB, 17 views)
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Old   June 12, 2012, 01:36
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can you provide the dbs file?
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Old   June 12, 2012, 02:44
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Ok I checked your dbs file, and your problem, can be resolved by using the cleaning tool (use clean short edges: first on the left) it will collapse the trailing edge.
But you have other problems:
you need to connect faces 27 and 47
and you also have problem with surfaces 40 and 28: For that delete volume up, and reconstruct it with remaining surfaces (sticht faces)
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Old   June 12, 2012, 03:01
Default Re:problem with importing geometry in Gambit
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Wow! Thank you so much for all this helpful points

If I understand correctly, you mean by deleting short edges I can merging the faces. Isn't it?
And about connecting faces 47 & 27, do you mean defining an interface between them in Zone section(green cube)?
And problem with surfaces 40 and 28, the cylindrical faces should be moving but the frustums are stationary. I thought they would be separate volumes, what's wrong?

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Old   June 12, 2012, 03:08
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make first a good mesh for steady. Then adapt your mesh for moving mesh.
-For deleting short edges, use cleaning tool: click on update (short edge), and click on auto.
Gambit will automatically collapse trailing edges
-For faces 47 and 27, just connect them (forced virtual)
-For 40 and 28, as I said below, generate a mesh for steady state first (so delete the volume, and reconstruct it)
Once your mesh is ok, compute, check if flowfield is ok, then work on the motion
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Old   June 12, 2012, 03:16
Default Re:problem with importing geometry in Gambit
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Thank you dear mAx!

I'll do all this and will announce you about the result. But there is a problem, I'm using Gambit version 2.3, I can not find here what you said about cleaning tool unfortunately.

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Old   June 12, 2012, 03:26
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I checked and Cleaning Tool was already available at release 2.1.
You can find it in Tools/Geometry Clean-Up
http://cdlab2.fluid.tuwien.ac.at/LEH...ide/mg0504.htm
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Old   June 12, 2012, 03:33
Default Re:problem with importing geometry in Gambit
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Oh,yes! I just found it
I should use the first item (clean up short edge), right?
Thank you very much dear mAx!

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Old   June 12, 2012, 03:34
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yes
update>auto
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Old   June 12, 2012, 03:36
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OK, thank you in advance!

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Old   June 12, 2012, 03:51
Default Re:problem with importing geometry in Gambit
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Dear mAx,
I do it as you said, but after cleaning up I lose 3 primary edges of airfoils(button airfoils)!
What's wrong?

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Old   June 12, 2012, 04:09
Default Re:problem with importing geometry in Gambit
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I did it on a new file and it worked correctly!
Thanks for your help mAx

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Old   June 12, 2012, 09:14
Default Re:problem with importing geometry in Gambit
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Hi dear mAx,
I tried it out and there is a similar problem that Gambit couldn't convert virtual volume/face/edge of blades to real.
What should I do?

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Old   June 13, 2012, 01:03
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you should use the cleaning tool, only when your topology decomposition is ready (I mean jjsut befor you start to mesh your model)
Indeed the cleaning tool, will give you finally a virtual entity and it is then no more possible to get a real entity (what you experienced)
Why do you want real entities?
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Old   June 13, 2012, 01:19
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Hi dear mAx,
I should subtract volumes to get appropriate domain as you saw. It it possible subtracting a virtual volume from a real one? And may it cause any problem in Fluent (virtual blades)?


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Old   June 13, 2012, 01:21
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no
that's why you need to keep real entities as late as you can, else you cannot handle boolean operations anymore (they are only available for real topologies)
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Old   June 13, 2012, 01:30
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OK, Thank you in advance!
I'll do that.


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Old   June 13, 2012, 04:04
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Hi dear mAx,
During meshing a discontinuity occurs as showed in figure. It seems that it is as a result of existence of two virtual and aslo two real edge in a face, isn't?
What should i do?

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Old   June 13, 2012, 04:38
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in the display options, make all volumes invisible, and display only blades.
Enable shaded modus, and check if the surfaces is ok (where you get degenerated cells)
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Old   June 14, 2012, 02:44
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Hi dear mAx,
I checked the blades as you said and found out a problem in my Solid Works model.
Now, I'm going to improve it and then try it again in Gambit.

Thank you in advance,

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