Mesh Expansion Factor value acceptable??

Danial Q · June 10, 2012, 20:53

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 |
+----------------------+---------------+--------------+--------------+

ghorrocks · June 11, 2012, 20:12

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.

Danial Q · June 11, 2012, 20:44

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

ghorrocks · June 12, 2012, 19:42

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.

Danial Q · June 13, 2012, 05:12

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

ghorrocks · June 13, 2012, 07:30

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.

June 10, 2012, 20:53	Mesh Expansion Factor value acceptable??	#1
Danial Q Senior Member Danial Join Date: Nov 2011 Posts: 179 Rep Power: 14	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 \| +----------------------+---------------+--------------+--------------+

June 11, 2012, 20:44	HI	#3
Danial Q Senior Member Danial Join Date: Nov 2011 Posts: 179 Rep Power: 14	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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June 11, 2012, 20:12		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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.

June 12, 2012, 19:42		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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.

June 13, 2012, 05:12	Hi	#5
Danial Q Senior Member Danial Join Date: Nov 2011 Posts: 179 Rep Power: 14	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

June 13, 2012, 07:30		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	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.