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-   -   help! grid check error (http://www.cfd-online.com/Forums/fluent/36450-help-grid-check-error.html)

Gary Holland April 21, 2005 16:07

help! grid check error
 
Hello there,

i'm hoping someone may be able to offer some advice before i tear my hair out!. i'm just trying to use gambit and fluent for the first time. i've managed to put a grid onto a simple 3d object but everytime i check the grid in the fluent start up section i get a warning saying: "WARNING: non-positive face area exist"

i'd be very grateful if someone could offer some pointers. thanks very much, gary.

pUl| April 21, 2005 19:38

Re: help! grid check error
 
Is your geometry Axisymmetric?

Gary Holland April 21, 2005 21:59

Re: help! grid check error
 
thanks for the reply. It is a flat (very thin) ellipse shaped volume with an inlet and outlet ports situated towards each end, perpendicular to the ellipse. i can manage to get a mesh of some sort, although i keep getting that warning when i try to open it in fluent....

pUl| April 22, 2005 08:36

Re: help! grid check error
 
So is it modeled axisymmetric? And if so, is your domain above or below the X-Axis?

Jason April 22, 2005 09:48

Re: help! grid check error
 
It's a 3D mesh, correct?

If so then the problem is the quality of your grid. In gambit, go to the volume mesh commands, and click "check mesh"... it looks like a check mark. Then select the volume and it will give some information on the mesh in the transcript window. The last few lines are probably going to say something about "XXX highly skewed elements" and maybe something about "XXX inverted elements". This is a poor quality mesh. Now what you have to do is find the problem area so you can start working out a solution. The icon on the bottom right corner of the screen is the Examine Mesh function. It looks like a yellow grid with a magnifying glass over it. You can play around with the options so they are set to your type of mesh (set display type to "Range", use "3D element" and select the right type of elements" and set Quality Type to "equiangle skew"). Towards the bottom of the examine mesh window are sliders that you can adjust to play around with what range of elements you are looking at, or you can click "Show Worst Element" and this will zoom in on the worst element (depending on the quality type you chose) in the mesh. Once you find where it is, then you can try and see why it's a problem and try to fix it. Once you find the problem and you need help fixing it, feel free to post any information on here and we'll try to help you out.

Hope this helps, and good luck, Jason

Gary Holland April 22, 2005 10:07

Re: help! grid check error
 
Very many thanks for your help and time guys. I'll try what you've suggested.

thanks again, gary.

Gary Holland April 22, 2005 11:20

Re: help! grid check error
 
Hi again,

Yes, I followed the steps that you suggested and found the 'worst element'. However, when i check the other 3d boxes (anything other than the cube), the worst element section dissapears? Are these 3d shapes part of the tri/hex etc that were part of the mesh set up? I don't think i'm using the 'examine mesh' window how it should be used as i'm still unsure of how to go about fixing my problem. any more advice would be most welcome! thanks for your time. gary.

khairy April 24, 2005 22:20

Re: help! grid check error
 
Dear Gary

be patient,cane u send a free hand sketch,or any drawing for the problem with all dimension ,and i will try it for u and send to u all the steps,have a good luck khairy-Egypt

Jason April 25, 2005 08:08

Re: help! grid check error
 
As long as your display type is "range" then I've never seen the "worst element" section disappear. Maybe you can only select one element type at a time to view. Which version of Gambit are you using?

When you did the mesh check, did it come up with any highly skewed or inversed elements?

Jason

Gary April 25, 2005 14:37

Re: help! grid check error
 
guys, thanks for the help. i followed your advice and also some online tutorials and have managed complete the model. i am now trying the animation.....

thanks again!!! gary.


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