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unwanted lines after extruding the 2D mesh

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Old   January 5, 2011, 14:05
Default unwanted lines after extruding the 2D mesh
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Hi,
In order to generate a 3D mesh (including 5 zones), I created a 2D surface and then meshed it and extruded this mesh along direction 0 0 1.
Result can be seen in Figure-1.
But looking at the Figure-2 (in which the lowest zone is turned on) and Figure-3 (in which only the CGC-T is visible) there are two unwanted groups of lines with the blue color (the lowest one is wanted and is CGC-T but the other two are unwanted).
I have no idea why these two groups of lines (they are not surface, or surface mesh) are created. Any idea?

The other question: If i import it into Fluent, will they affect the solution procedure/results?

Thanks
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Old   January 5, 2011, 14:09
Default Figures
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Sorry, I am attaching the figures here.
Attached Images
File Type: jpg 1.jpg (90.2 KB, 18 views)
File Type: jpg 2.jpg (89.0 KB, 14 views)
File Type: jpg 3.jpg (87.1 KB, 10 views)
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Old   January 8, 2011, 15:39
Default 2D to 3D...
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Hey Masoud,

Extrude takes your original mesh and adds a dimension... 2D becomes 3D, 1D becomes 2D, 0D becomes 1D. In other words, shells produce volume elements, lines become side shells, and points become side lines...

So, you must have had that part as line elements in the original 2D mesh, they were simply extruded into 3D shells on the side.

As shells, they certainly will affect your Fluent solution. They could be walls or merely internal walls that separate different volumes (you probably want these). In your case, the same part is used as both an internal and external wall, so you will certainly have a problem. I can really tell, but you may have an even bigger problem if you don't have shells around all the volume elements. Fluent actually needs shells around all volumes (to contain them), and not having them will give a null pointer error.

Go back to your 2D mesh and check that you have line elements around all your shells so that when you extrude, those perimeter lines become enclosing shells around each section. Lines between shells should be in unique parts that can become internal walls in Fluent. The line elements form naturally with the patch conforming mesher, but you must associate edges to curves if you started with Hexa blocking.

For extruding from multiple surfaces, I suggest you use inherited for all the parts (including volume). This will actually put your volume elements in the parts of your shells, but you can then go thru and turn on volume elements and each part and assign the volume elements to a new part manually...

Best regards,

Simon
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