[GAMBIT] Stairstep meshing in Gambit

Zato_Ichi · June 9, 2011, 08:27

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, 11:18

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, 15:55

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, 02:49

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, 06:57

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, 07:56

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: http://my.fit.edu/itresources/manual...guide/tg03.htm
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

DEAR Max,

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

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?
etc...
etc...
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

June 9, 2011, 11:18		#2
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	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? __________________ In memory of my friend Hervé: CFD engineer & freerider

June 10, 2011, 02:49		#4
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	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) __________________ In memory of my friend Hervé: CFD engineer & freerider

June 10, 2011, 07:56		#6
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	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: http://my.fit.edu/itresources/manual...guide/tg03.htm Remember you have to mesh first the elbow and then the other volumes (because of projection) __________________ In memory of my friend Hervé: CFD engineer & freerider

November 14, 2012, 07:36		#8
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	pictures may help __________________ In memory of my friend Hervé: CFD engineer & freerider

November 14, 2012, 08:59		#10
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	why do you want to use stairstep? __________________ In memory of my friend Hervé: CFD engineer & freerider

November 14, 2012, 06:31		#7
zaynah04 Senior Member zaynah K. Join Date: Jun 2012 Location: Mauritius Posts: 138 Rep Power: 14	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.

November 14, 2012, 08:53		#9
zaynah04 Senior Member zaynah K. Join Date: Jun 2012 Location: Mauritius Posts: 138 Rep Power: 14	DEAR Max, 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?

November 14, 2012, 09:01		#11
zaynah04 Senior Member zaynah K. Join Date: Jun 2012 Location: Mauritius Posts: 138 Rep Power: 14	because no other option is meshing my domain and building..

November 14, 2012, 09:05		#12
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	May I see how your geometry looks like? __________________ In memory of my friend Hervé: CFD engineer & freerider

November 14, 2012, 09:58		#14
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	I meant the buildings... __________________ In memory of my friend Hervé: CFD engineer & freerider

November 14, 2012, 10:02		#15
zaynah04 Senior Member zaynah K. Join Date: Jun 2012 Location: Mauritius Posts: 138 Rep Power: 14	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..

November 14, 2012, 10:05		#16
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	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 __________________ In memory of my friend Hervé: CFD engineer & freerider

November 14, 2012, 10:07		#17
zaynah04 Senior Member zaynah K. Join Date: Jun 2012 Location: Mauritius Posts: 138 Rep Power: 14	yes i understand. but i have already tried all combinations only Hex and Staircase works..

November 14, 2012, 10:10		#18
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	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? etc... etc... And finally did you read error messages from gambit? __________________ In memory of my friend Hervé: CFD engineer & freerider

November 14, 2012, 10:26		#19
zaynah04 Senior Member zaynah K. Join Date: Jun 2012 Location: Mauritius Posts: 138 Rep Power: 14	error message from gambit was that high skewness... and i did most of the above.

November 14, 2012, 10:29		#20
-mAx- Super Moderator Maxime Perelli Join Date: Mar 2009 Location: Switzerland Posts: 3,297 Rep Power: 41	If you want you can provide me the dbs file __________________ In memory of my friend Hervé: CFD engineer & freerider

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