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Mesh Expansion Factor value acceptable??

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Old   June 10, 2012, 20:53
Default Mesh Expansion Factor value acceptable??
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Danial
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Hi ,
This is my mesh details and i am worried about Exp factor value as document states that it (Range) should be less than 20. I am using Hexdominant mesh for homogeneous multiphase problem including free surface and thermal energy model.
Could any one please tell me if it is acceptable or total failure?? it will save me a lot of time. Thanks

+--------------------------------------------------------------------+
| Mesh Statistics |
+--------------------------------------------------------------------+
| Domain Name | Orthog. Angle | Exp. Factor | Aspect Ratio |
+----------------------+---------------+--------------+--------------+
| | Minimum [deg] | Maximum | Maximum |
+----------------------+---------------+--------------+--------------+
| D1 | 9.2 ! | 208 ! | 74 OK |
| D2 | 5.6 ! | 399 ! | 98 OK |
| Global | 5.6 ! | 399 ! | 98 OK |
+----------------------+---------------+--------------+--------------+
| | %! %ok %OK | %! %ok %OK | %! %ok %OK |
+----------------------+---------------+--------------+--------------+
|D1 | <1 <1 100 | <1 1 99 | 0 0 100 |
| D2 | <1 1 99 | <1 1 99 | 0 0 100 |
| Global | <1 <1 100 | <1 1 99 | 0 0 100 |
+----------------------+---------------+--------------+--------------+
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Old   June 11, 2012, 20:12
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Glenn Horrocks
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It is just a warning. But free surface models are pretty sensitive to high expansion ratios like this so you will probably have to improve your mesh quality.
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Old   June 11, 2012, 20:44
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Here are details of mesh and most importantly, domain's dimensions are 200 x 200 x 40 MICRONS (fluid-solid domains).Do you think I should refine my mesh a bit more. I have used Hexdominant with program controlled option.

Global Statistics :
Global Number of Nodes = 557411
Global Number of Elements = 530304
Total Number of Tetrahedrons = 2101
Total Number of Prisms = 1136
Total Number of Hexahedrons = 521023
Total Number of Pyramids = 6044
Global Number of Faces = 66578

Thanks
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Old   June 12, 2012, 19:42
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There are no general rules, especially if you are modelling an unusual case (your small geometry means general rules of thumb probably don't work). You will have to do sensitivity checks and work out for your case.
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Old   June 13, 2012, 05:12
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glen, thanks but could you please suggest me some document/ book to study about sensitivity analysis as I am new guy in the town .
thanks
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Old   June 13, 2012, 07:30
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Some suggestions:

1) Do a literature search.
2) Do your own models of stuff with accurate analytical or experimental results, such as pressure in a spherical drop or capilliary flow or what ever is appropriate. When you get these simple models accurate you will know what your more complex model will require.
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