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Zato_Ichi June 9, 2011 07:27

Stairstep meshing in Gambit
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Hello !

I have a quiet simple geometry, but i cannot find the way how to mesh it with stairstep type. There is a pipe (H=0.5, R=0.01) and rectangular hexahedron (W=0.5 D=0.3 H=0.3), and i want to mesh the pipe with stairstep, but i don't know how to connect them back after that. Than i'm trying to mesh both pipe and hexahedron with required precision (Interval size 0.001) it cannot satisfy memory request. So i need to refine mesh in hexahedron, but idon't know how. Stairstep meshing is necessarily in my case because pipe has a complex shape with corners and curves in general.

Thank you for help!

-mAx- June 9, 2011 10:18

I am not familiar with stairstep (never used), but do you want only stairstep mesh because of your solver or whatever?
Or do you want staistep because you think this is the only wayto mesh your stuff with hexa?
Ca you display your pipe with complex shape?

Zato_Ichi June 9, 2011 14:55

1 Attachment(s)
Well, it should be something like that. Worse than pipe has \Omega - like shape, but i haven't even tried to make it. In case shown on pic leads of pipe could be meshed with cooper scheme, but middles meshes only with tetrahedra cells. I'm investigating shockwaves propagation in pipe and following jet simulation, so i need mesh as symmetrical as possible as asymetric influences on jet.

-mAx- June 10, 2011 01:49

If you decompose your domain you won't have any problem to mesh it with hex or cooper.
Just split before and after elbows.
Then if you want symmetric mesh, you can work with one half of your domain (symmetry), mesh it and once your grid is ready, you can reflect your domain (with mesh)
You get the whole domain with reflected grid from symmetry (>> symmetric grid)

Zato_Ichi June 10, 2011 05:57

2 Attachment(s)
Thank you very much for your replies !

I made decomposition as you recommended, now direct parts are meshing with hex, but elbow not. Maybe i made something wrong ? While meshing Cooper error appears : regular side face (s) mesh for projecting volume could not found.

About symmetry, actually i need it about the pipe axis to avoid asymmetry on the pipe output.. so pave scheme is not good too, but it is only scheme that can mesh endings with hex. I made boundary condition on the end and it seems that it could not be meshed symmetrically with hex.

Best regards !

-mAx- June 10, 2011 06:56

From your first picture you can see 3 edges . From here it seemed you generated a local axis-system.
So split elbow with surfaces made from edges. Elbow will be splitted into 3 subvolumes.
Then check this tutorial:
Remember you have to mesh first the elbow and then the other volumes (because of projection)

zaynah04 November 14, 2012 06:31

i found that the stairstep meshing is rather strange.
it creates a new boundary for me and also the result is not good.

any suggestions please.

my interval size was 12 and Hex and stairstep.

-mAx- November 14, 2012 07:36

pictures may help

zaynah04 November 14, 2012 08:53


thanks for replying. i had not proceeded with the stairstep as a repeat of my buildings and domain have been done they were called f_285 etcc. this had been automatically generated as soon as i apply stairstep function..

can you please elaborate on the use of this function?

-mAx- November 14, 2012 08:59

why do you want to use stairstep?

zaynah04 November 14, 2012 09:01

because no other option is meshing my domain and building..:(

-mAx- November 14, 2012 09:05

May I see how your geometry looks like?

zaynah04 November 14, 2012 09:40

1 Attachment(s)
hi this is my domain and you can see two has been generated.

-mAx- November 14, 2012 09:58

I meant the buildings...

zaynah04 November 14, 2012 10:02

i do not have it on my pc right now as all my work is done at the university..

i had only this one which i had meshed with stairstep.
you can clearly see another domain has been generated..:(

-mAx- November 14, 2012 10:05

yes I see it, but it is stairstep.
For sure you can mesh it with combination of tetra/hexcore and size-function.
But also for sure, you cannot mesh on the fly, and you will have to prepare your geometry

zaynah04 November 14, 2012 10:07

yes i understand.
but i have already tried all combinations only Hex and Staircase works..:(

-mAx- November 14, 2012 10:10

did you split your volume?
did you merge some surfaces for deleting sharp edges?
did you apply size function on small entities for preventing cell skewness?
And finally did you read error messages from gambit?

zaynah04 November 14, 2012 10:26

error message from gambit was that high skewness...

and i did most of the above.

-mAx- November 14, 2012 10:29

If you want you can provide me the dbs file

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