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Old   March 8, 2014, 18:52
Default High aspect ratio
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Jack Holmes
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Hi all,

I am trying to create a dynamic mesh but keep getting the error

WARNING: The mesh contains high aspect ratio quadrilateral,
hexahedral, or polyhedral cells.
The default algorithm used to compute the wall
distance required by the turbulence models might
produce wrong results in these cells.
Please inspect the wall distance by displaying the
contours of the 'Cell Wall Distance' at the
boundaries. If you observe any irregularities we
recommend the use of an alternative algorithm to
correct the wall distance.
Please select /solve/initialize/repair-wall-distance
using the text user interface to switch to the
alternative algorithm

How do I fix this as when I preview my dynamic mesh I get a negative volume.

Any help and advice would be great.

Thanks all,

Jack
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Old   March 9, 2014, 16:14
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Mack
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Hi Jack,

Are you using a structured or unstructured mesh? Are you using a low Reynolds approach? If yes, do not worry about this message, even though you can correct this repairing the wall distance via TUI (as stated in the error message).
However, if you are using an unstructured mesh and a high Reynolds approach then you may have bad quality elements (very skewed ones). You must check your mesh when uploading it on Fluent. You can also smooth it, if this is the case.
As your geometry is very simple I would recommend you to use a block structured mesh with an o-grid.

Regards,
Mack
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Old   March 10, 2014, 06:26
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Jack Holmes
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Can i ask for your email and send you the mesh to see if theres anything you can do.

If not, no worries and thank you anyway

Jack
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Old   March 10, 2014, 16:00
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Mack
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Hi Jack,

Sorry but I do not have Fluent/ICEM anymore. Did you take a look on the 2D cylinder mesh tutorial?
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Old   March 12, 2014, 22:31
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ganhai
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Hi,Mack
I also get into the same trouble with Jack.My model with unstructured mesh and big Reynolds approach.
How can I improve my mesh quality .
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Old   March 13, 2014, 18:40
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Hi Ganhai,

Have you tried to smooth the mesh? You can do it either on your meshing program or on fluent. If you check the mesh on fluent prior to the movement and everything is ok, then it means that your moving parameters are not ok. Do not forget to apply movement to the cylinder volume and not just to the walls. Take a look on the tutorial I mentioned before, it may help.

Regards,
Mack
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Old   March 13, 2014, 21:14
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ganhai
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Hi Mark,Thank you for your reply!Here i give my icem model for you.I really appreciate you can take some time have a look.
Thanks again.
france
Attached Images
File Type: jpg 360??20140314083000309.jpg (86.8 KB, 82 views)
File Type: jpg 360??20140314083037165.jpg (89.7 KB, 58 views)
Attached Files
File Type: zip ICEMCFD-france.zip (84.5 KB, 12 views)
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Old   March 14, 2014, 10:06
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Hi Ganhai,

Is that a hollow cylinder? Is it 2D or 3D?
Sorry, but I could not understand your geometry with these pictures.
It seems that you have very stretched elements, so you should try to square them increasing the number of cells on the edges.
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Old   March 14, 2014, 20:48
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ganhai
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Hi,Mack
It is 3D and the surface of the up and down are sphere.If I increasing the number of cells on the edges the whole model will have several millions elements.Then my compute nearlly can't deal with it.So,Is there any way I can solve this problem.
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Old   March 15, 2014, 11:08
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Hi Ganhai,

Well, as your geometry is quite symmetric you can take advantage of this and simulate just a fraction of the domain.
Try to simulate just a "piece of cake", applying symmetry condition to both sides. It will save you enormous computational effort.
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Old   March 16, 2014, 21:18
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ok,Mack. I will try it.No matter how,I will let you konw the result.Thanks again.
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dynamic mesh, fluent, high aspect ratio, negative volume error

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