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Connecting the interiors of two nested objects

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Connecting the interiors of two nested objects

Posted by Mark Weber at July 29. 2020

Summary

If I have a small box inside a big box, how do I remove on of the faces of the small box and connect the two volumes together?

Detail

I am doing acoustic simulation and want to connect the air inside a tube to the air outside the tube. I have search a lot and tried a lot, but have not found the secret. The problem can be simplified by considering a box in a box. I would like to remove one face of the inner box so the volume in the big box and small box are one.

I have joined the nested boxes together using FUSION. That is not what I want.

I have joined them together using PARTITION. Then I EXPLODE the resulting partition and select only the parts I want leaving out the face between the two volumes. These selected parts I use to create another partition. If I select only faces, I get a result that has only 2d parts and I cannot mesh it for 3d. If I select faces and solids for the partition, I get two separate solids and it puts a face in that I did not select.

I tried EXTRACT and REBUILD. When I select the face to extract it also extracts the solids on either side and the result rebuild is only 2d and will not properly mesh.

Thank you for helping,

Mark

 

Re: Connecting the interiors of two nested objects

Posted by Saint Michael at July 30. 2020

Hi Mark

You can achieve you goal this way. Remove one face of the small box, for example by creating a group of all but one faces. Then partition the big box and the group.

St.Michael

Re: Connecting the interiors of two nested objects

Posted by Mark Weber at July 31. 2020

Dear St. Michael,

Thank you very much for your quick and very useful reply. I had to learn to make the big box the main object in the partition and then the 5 faces of the small box the tool objects. I also learned I did not want to check the box "keep shapes of lower type". I also tried repair>shape processing. It found 3 or 4 things to fix. For whatever reason when I tried to create a group, there was no sub-shapes to select. So I did the partition directly - not using a group.

 

I am having a problem that may or may not be important.Occasionally I get a window that pops up and says

"Fatal Error  Unknown exception"

When you click OK. you get another widow that says

"Fatal error SIGSEGV 'segmentation violation' detected. Address 8"

 

It seems to be random as it does not seems connected to any particular command I execute. It may be connected to meshing or geometry.

 

Once again thank you for your timely response.

 

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Re: Connecting the interiors of two nested objects

Posted by Mark Weber at July 31. 2020

OK. I guess I still have a problem. I created a mesh using NetGen 1D-2D-3D and then computed the mesh.

It responds with "Mesh Computation succeed"

but it also says "Global 2d algorithm is missing"

When I using "normal" objects (those not modified as I described above) my meshing procedure works fine.

Any help here is appreciated.

 

Re: Connecting the interiors of two nested objects

Posted by Mark Weber at August 02. 2020

I did a little bit more digging. The "Fatal error Unknown exception" is apparently some sort of driver error. I made a modest attempt to fix it without success. The software appears to be able to live with this error although it is annoying.

The "Global 2d algorithm is missing" is a real thing. I took advice from this post https://www.salome-platform.org/forum/forum_10/464552462.

 

Re: Connecting the interiors of two nested objects

Posted by Mark Weber at August 02. 2020

One more note. The repair operation I did above was not needed and modified the study in an unwelcome way.

Re: Connecting the interiors of two nested objects

Posted by Nabil Ghodbane at August 03. 2020

Hi Mark,

can you describe the steps which lead to the fatal error message that you experience occasionnaly?

This information, in addition to the OS/platform and SALOME version you used are of important means and will help us to reproduce the issue on our side and escalate it to our developers team.

Thanks for your feedback.

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