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skewness of polyhedral elements

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Old   August 20, 2007, 19:39
Default skewness of polyhedral elements
  #1
Neo
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Anyone know how to determine the skewness of the polyhedral elements? or Is it the same method for others shape. I converted tetra mesh into polyhedral. The outcome is that the maximum skewness became zero.
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Old   August 20, 2007, 20:47
Default Re: skewness of polyhedral elements
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Carlos
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Hi,

Yes I'm sure you measure skewness in the same way in Fluent. The main advantage of polyhedral cells is that they have a much lower skew value, thats one of the reasons why poly-meshes give faster simulation times. Try looking at average values too.

Regards,

Carlos.
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Old   August 21, 2007, 02:36
Default Re: skewness of polyhedral elements
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Razvan
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Unfortunately, the "skewness" concept is not applicable to polyhedral cells just as for the other, ordinary shapes like tetrahedron or hexahedron. The reason for that is very simple: polyhedral cells may have 7, 8, 9, an so on, up to 16 (perhaps...) faces, and one cannot easily define an ideal shape to be compared with all these cell shapes. Nevertheless, there is at least one quality criterion defined in FLUENT that applies to polyhedral cells, but it can be accessed only through TUI: the squish index.

Two possible quality criteria (that could be inplemented, in my opinion):

- "sphereness" = nodal averaged normal distance to the circumscribed sphere (the closer to 0, the better the quality of the polyhedral cell);

- "convexity/concavity" = the normal distance between any node and a face constructed using the surrounding nodes only (should be >=0, if calculated considering the positive direction the normal direction pointing outside of the cell).

I repeat, these criteria are not implemented in FLUENT, they are just suggestions for the developers.

All the best,

Razvan
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Old   August 21, 2007, 18:52
Default Re: skewness of polyhedral elements
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Neo
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Thank you very much guys. Can you tell me how monitor "the squish index"?. Can you tell me some commands which lead to it?
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Old   August 22, 2007, 02:18
Default Re: skewness of polyhedral elements
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Razvan
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After converting your grid to polyhedral, type "grid/quality" in the TUI, and automatically the solver will calculate this parameter for all the faces and the cells of the grid.

Razvan
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Old   August 22, 2007, 04:08
Default Re: skewness of polyhedral elements
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Neo
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thanks for the answer.
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Old   September 4, 2007, 10:37
Default Re: skewness of polyhedral elements *NM*
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chouaib
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