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Old   June 22, 2010, 03:04
Default Edit an IGS file
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I have an IGS file for half an aircraft. The symmetry plane is supposed to be on y=0 but the coordinates are not exactly zero due to some roundoff errors. Is it possible to edit the coordinates using some software ?
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Old   June 22, 2010, 11:45
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It is best to do this in your CFD package by creating a custom CSYS (which is offset, as you say).

The reason why is: most CAD programs do not follow the IGS format exactly, and you may end up with translation errors (on import, and/or export).

If you still want to do it, I know that ProEngineer allows you to export with a custom CSYS.
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Old   June 26, 2010, 16:48
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Hi Praveen:

While it might be possible to find some software that will import your IGES file, enforce a Y=0 condition on the symmetry plane, and export a new file I'm not aware of one off the top of my head.

It is theoretically possible to literally edit the IGES file by hand in vim or emacs or your favorite editor. After all, it's only an ASCII file. But finding all the Y coordinates that should be zero is a complex task requiring a knowledge of the IGES spec. (Which is a really fun read, trust me.)

Hopefully your mesh generator has the capability to project certain portions of the grid so I would create a plane at Y=0 and then project the edges that should line on the symmetry plane onto the plane.

Not much help, I know. Best of luck.
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Old   June 26, 2010, 23:50
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Thanks for the tips. I did look at the igs file and could locate some of the problematic points. But not all of them seem to have exactly the same y coordinate. If all points have y<0 instead of y=0, I could use a plane and trim the CAD model (will try this next).

PS: Is there any forum dedicated to pointwise ?
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Old   June 27, 2010, 13:49
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If the symmetry plane points are off Y=0 by an amount that could be considered a small tolerance, trimming might not work. After all, trimming is simply a tolerance based operation and the scatter you see in the symmetry coordinates might cause the trimming operation to fail.

If you were using Gridgen instead of Pointwise, there's a script that enforces a symmetry plane. You can find it in our Glyph Script Exchange web site, www.pointwise.com/glyph.

There's no forum dedicated to Pointwise or meshing. We've discussed that with the CFD-Online people on numerous occasions but they don't want to fragment the forums too much at this time.
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Old   July 5, 2010, 02:26
Default Issues with importing a IGES file in gridgen
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Quote:
Originally Posted by jchawner View Post
If the symmetry plane points are off Y=0 by an amount that could be considered a small tolerance, trimming might not work. After all, trimming is simply a tolerance based operation and the scatter you see in the symmetry coordinates might cause the trimming operation to fail.

If you were using Gridgen instead of Pointwise, there's a script that enforces a symmetry plane. You can find it in our Glyph Script Exchange web site, www.pointwise.com/glyph.

There's no forum dedicated to Pointwise or meshing. We've discussed that with the CFD-Online people on numerous occasions but they don't want to fragment the forums too much at this time.
Hi

My problem is kind of similar to the one being discussed in this thread in the context that I am trying to mesh a geometry in gridgen by importing the database as an IGES file. But on doing this some of the faces come out detached and hence on trying to create a mesh for those adjoining faces, the meshes overlap each other. Could you suggest something that could help?

Thank you.

Digvijay
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Old   July 5, 2010, 08:40
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Dig:

If I understand your problem correctly, you import an IGES file and get many surfaces. When you mesh those surfaces the resulting surface meshes (domains in Gridgen terminology) don't connect and instead have gaps and overlaps.

You have two choices.

You can use the Merge command to convert two connectors on a seam between database surfaces into a single connector. That will result in the domains being connected so they can be used on the face of a block, etc. Merge can perform many operations like merging two connectors, two nodes, and a node and a connector (like for a t-junction).

Your second option it to take your database and create a solid model out of it (see, Database, Create, Model). This implicitly closes the gaps and overlaps in the geometry so that when you mesh it the grid is fully connected.

Hope this helps.
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Old   July 6, 2010, 05:19
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Quote:
Originally Posted by jchawner View Post
Dig:

If I understand your problem correctly, you import an IGES file and get many surfaces. When you mesh those surfaces the resulting surface meshes (domains in Gridgen terminology) don't connect and instead have gaps and overlaps.

You have two choices.

You can use the Merge command to convert two connectors on a seam between database surfaces into a single connector. That will result in the domains being connected so they can be used on the face of a block, etc. Merge can perform many operations like merging two connectors, two nodes, and a node and a connector (like for a t-junction).

Your second option it to take your database and create a solid model out of it (see, Database, Create, Model). This implicitly closes the gaps and overlaps in the geometry so that when you mesh it the grid is fully connected.

Hope this helps.

Thank you so much for your suggestion. It really worked. I really appreciate the help.

Dig
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Old   July 16, 2010, 08:01
Default Volume Mesh in Pointwise
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Hi

I had a doubt regarding Pointwise. I was working on creating a structured mesh for Onera M6 Wing for practice and I was having issues with the final steps of creating the block and meshing it. Actually when I selected all the domains that should have resulted in a closed volume, and pressed the Assemble Block Tab, 1 block was created but it didn't use 6 domains which formed the lower half of the grid. Now from the tutorials I found out that the next step is to initialize the block. I did that but the grid still looked like containing just surface meshes. I tried changing the attributes of the block but that didn't work. Could you outline the procedure for the creation of the block and its meshing after creating the domains. I would really appreciate the help.

Dig

Quote:
Originally Posted by jchawner View Post
Dig:

If I understand your problem correctly, you import an IGES file and get many surfaces. When you mesh those surfaces the resulting surface meshes (domains in Gridgen terminology) don't connect and instead have gaps and overlaps.

You have two choices.

You can use the Merge command to convert two connectors on a seam between database surfaces into a single connector. That will result in the domains being connected so they can be used on the face of a block, etc. Merge can perform many operations like merging two connectors, two nodes, and a node and a connector (like for a t-junction).

Your second option it to take your database and create a solid model out of it (see, Database, Create, Model). This implicitly closes the gaps and overlaps in the geometry so that when you mesh it the grid is fully connected.

Hope this helps.
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Old   July 16, 2010, 08:17
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Dig:

I cannot tell from your description what exactly is happening. If the Assemble command creates a block (i.e. a block appears in the List) the grid should exist too, especially for a structured grid. Did you use the Examine command to look at the volume points?

As for blocks for the upper and lower surface of the wing, I don't know what you topology looks like so again I can't tell what you're seeing. In general, Assemble creates the simplest topologies it can from the selected entities. If you need something more complex, you can use the Assemble Special command with which you can explicitly select the domains on each of the block's six faces.
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Old   July 21, 2010, 07:29
Default Merging Blocks in Gridgen
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Hi

I was finally successful in creating blocks. I have attached a snapshot of the geometry. I have created 2 block one for the upper half and one for the lower half. Is there a facility in gridgen using which I can merge both these blocks into one?
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File Type: jpg Onera.jpg (90.8 KB, 21 views)
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Old   July 21, 2010, 08:16
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Assuming, of course, that the topology you've used allows the blocks to be joined.
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Old   July 21, 2010, 08:23
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Sorry I forgot to mention its an 0-H topology. And I have already tried the "join". Its just says joined 0 structured block(s) to give 0 structured block(s. 2 structured unused. Is there some other function that could help?
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Old   July 21, 2010, 08:30
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If your O-H topology doesn't allow the blocks to be joined (because joining them doesn't result in a single, consistent, structured grid) then they can't be joined.
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Old   July 21, 2010, 10:55
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I thought I should explain my the grid in more detail. Actually the Wing Root is on the Symmetry plane and and after sweeping it by a specific angle, the wing tip is finally collapsed onto a single line which is then swept til the end of the grid in y direction. So this collapsed plane (formed by sweeping the collapsed wing tip in y direction) is a part of the upper and the lower block (shown in the fig attached earlier). Is it possible that the collapsed plane might be causing the issue?
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Old   July 21, 2010, 11:26
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Any of a number of factors might be causing the problem but I can't tell without having the grid file. At this point I think it's best that you contact our Tech Support Team directly at support@pointwise.com.
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Old   July 21, 2010, 12:11
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Thanks for all the help. I will definitely contact them. Thank you so much.

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