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Internal error in geometry decompositon: problem with just 2 elements in model!

Posted 15 apr 2013, 18:21 GMT-4 Version 4.3a 3 Replies

Sri Puranam
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Hi Everyone:

I am trying to build a complicated 3-D model with many channels and such but I ran into a problem very early on. I just have one block attached to one hexaheadron. I am unable to form a union. I must be missing something very basic. Could someone help me out? I have attached my mph file.

Thanks!
Sri.

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3 Replies Last Post 16 apr 2013, 11:55 GMT-4
John H.
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Posted: 1 decade ago 16 apr 2013, 08:13 GMT-4
The documentation of the "Hexahedron" geometry object says "Vertices 1–4 are the vertices of the bottom face in clockwise order." It makes a similar statement about the top face. Now, I have no idea what "clockwise order" is supposed to mean in this context, but I went ahead and just inversed the order of the vertices (both faces). Suddenly it worked.

I noticed that the geometry sequence also works with the vertices in the original order if you switch from the "CAD Import Module" geometry kernel to the "Comsol" kernel. Looks like a bug to me...

The documentation of the "Hexahedron" geometry object says "Vertices 1–4 are the vertices of the bottom face in clockwise order." It makes a similar statement about the top face. Now, I have no idea what "clockwise order" is supposed to mean in this context, but I went ahead and just inversed the order of the vertices (both faces). Suddenly it worked. I noticed that the geometry sequence also works with the vertices in the original order if you switch from the "CAD Import Module" geometry kernel to the "Comsol" kernel. Looks like a bug to me...

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Sergei Yushanov Certified Consultant
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Posted: 1 decade ago 16 apr 2013, 08:43 GMT-4
Sri,

Another way to get around “Form Union” issue in your geometry is to use Work Plane Geometry and Extrude options, as shown in the attached mph file. For better visualization of your geometry, clear “Preserve aspect ratio” in the Camera View, as shown in the attached picture.

Please realize that extra care should be taken to build good quality mesh for this type of geometry.

Regards,
Sergei
Sri, Another way to get around “Form Union” issue in your geometry is to use Work Plane Geometry and Extrude options, as shown in the attached mph file. For better visualization of your geometry, clear “Preserve aspect ratio” in the Camera View, as shown in the attached picture. Please realize that extra care should be taken to build good quality mesh for this type of geometry. Regards, Sergei
Sri Puranam
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Posted: 1 decade ago 16 apr 2013, 11:55 GMT-4
John: I fixed the geometry by switching the order of the verticies and it worked for me too. Thanks for the tip!

Sergei: My final geometry is a complex 3-D geometry which does not lend itself easily to extrusion. Just for these two elements, I tried extrusion and it worked. There were no errors. I have to now decide which of the two proposed solutions I will end up using.

Thanks to both of you.
Sri.
John: I fixed the geometry by switching the order of the verticies and it worked for me too. Thanks for the tip! Sergei: My final geometry is a complex 3-D geometry which does not lend itself easily to extrusion. Just for these two elements, I tried extrusion and it worked. There were no errors. I have to now decide which of the two proposed solutions I will end up using. Thanks to both of you. Sri.

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