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snappyHexMesh: Feature snapping of thin membrane edge

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Old   June 22, 2012, 19:01
Default snappyHexMesh: Feature snapping of thin membrane edge
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Guenter Bartsch
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Dear all,

attached to this post is a small test case of a thin membrane I am trying to mesh using snappyHexMesh. while the result overall is good, I noticed the edges are very rough. first intuition was to use a feature edge so snappyHexMesh would snap elements to the exact surface, but clearly that is not working - see screenshot attached.

anybody have an idea what could be wrong here?

thanks,

guenter
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File Type: jpg snappy_feature_edge.jpg (72.5 KB, 191 views)
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File Type: zip snappy_feature_edge.zip (23.4 KB, 63 views)
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Old   June 25, 2012, 11:39
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Dominic Britto Irudayaraj
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Hai Guenter ,

Detected 0 feature points, could be the first point to fix, so

Could you try to use the attached emesh file? or even in your eMesh file replicate the edge list to three times.

( during the initial check, it seems the way Snappy took the points is bit different.Meaning to detect an edge (0 1), you have to put this edge for three times!!!

I hope this can help in using the feature edges properly.


Best regards,
Dominic Britto & Bernhard !
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Old   June 25, 2012, 11:40
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Dominic Britto Irudayaraj
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pls see the attachment.
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File Type: gz Mem_down.eMesh.gz (1.1 KB, 86 views)
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Old   June 26, 2012, 09:31
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Dominic Britto Irudayaraj
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Hai Guenter,

It seems for a thin surface the Edge list have to be duplicated min 1 more time.

see the attached pngs, for further comparison btn single edge list - double edge list - double edgelist with tol 10 & 0.01.

But still the snapping is not done very perfectly, probably, this surface is continuously changing in angle in 3D and probably not easy for the snappy to catch the edges in a smoother way, as the initial blocks are done in an orthogonal manner!

Some more suggestions form other users also expected!!!

Thank you,
Dominic Britto.I
Attached Images
File Type: jpg SingleEdgelist_tol1.jpg (85.8 KB, 177 views)
File Type: jpg DoubledEdgelist_tol10.jpg (87.6 KB, 156 views)
File Type: jpg DoubledEdgelist_tol0.01.jpg (86.9 KB, 147 views)
File Type: jpg DoubledEdgelist_tol1.jpg (87.6 KB, 162 views)
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Old   June 26, 2012, 13:41
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Guenter Bartsch
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dominic,

very nice work! thanks for looking into this, definitely the idea to have the edge list twice is a big step forward. i am wondering why this is necessary - mabe thin, one-sided objects are not really supported - would be interesting to see if one creates a - still very thin - two-sided version of this shape?

thanks again and best regards,

guenter
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Old   December 18, 2012, 03:03
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Robert
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Hi Dominic,

why does it help to double the edge list? I've got a similar problem with a pipe with a diameter of 1 cm placed under a large desk, which snappy refuses to mesh at all. Even replicating the list ten times won't help. :/

Thanks, Robert

EDIT: I still don't know WHY, but that replication-trick really did it now! Thank you so much!

Last edited by vainilreb; December 19, 2012 at 04:17.
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Old   February 18, 2013, 12:44
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Nolwenn
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Thanks for this information, it helps a lot !
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