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Old   September 25, 2002, 17:01
Default surface mesh is "self-intersecting"
Chris F
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I'm modelling flow from a thin-walled tube with holes in its walls. A previous model with nearly identical geometry worked fine but with a slightly revised geometry I'm having the following problem. (The locations of the errors seem independent of the geometry change.)

When trying to write a definition file, a fatal error occurs while the volume mesh is being created. The errors read "surface mesh is self-intersecting" and "surface mesh overlaps itself". When I zoom in close to the geometry at the locations of the errors, I see nothing unusual in the view screen. Increasing mesh resolution in the problem areas does not seem to help.

Please advise!

Thanks, Chris
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Old   September 26, 2002, 06:57
Default Re: surface mesh is "self-intersecting"
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Do you use inflation on the thin surfaces? If so, delete it.

I have faced similar problems when I used cutout solids and several connected subdomains that contained thin surfaces. Does anyone know how to create inflation on such thin surfaces, while the inflation continues through other domains/subdomains on other thin surfaces or solid walls?

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Old   September 26, 2002, 08:46
Default Re: surface mesh is "self-intersecting"
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Astrid, you can pust inflation on thin surfaces, but you do need to make sure that the cell size above the thin surface is sufficiently small to fit in the defined sub domain given you inflation layer will take up a portion of that volume. There was a problem with this orriginally in the NT version of CFX, however that was fixed in on of the CFX5.5 patches.

You also need to take care that you use a triangular mesh control over your thin surface. If you specify a surface mesh control on your thin surface this may not be enough to reduce the size of your local mesh to fit inside the sub domain, especially if your global edge length is large. So a better way would be to use a set of triangular mesh controls with an appropriate mesh size and radius of influence to ensure that the cells fit in the sub domain.

Another possible cause for the over lapping surface mesh can be due to the definition of a solid sitting on top of another solid. Sometimes build does not pick up the fact that the two solids have a common interface surface, and so the surface mesher will attempt to mesh the top of the one solid as well as the base of the solid that sits on top (hoep this makes sense). The way around this is to ensure that the one solid is constructed using what would be the common face of the other solid. If you look at the mesh in these areas you can usually see an overlap.

Hope this helps

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