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[GAMBIT] sweeping 2D Boundary Layers

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Old   June 12, 2012, 04:45
Default sweeping 2D Boundary Layers
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Hello,

I have difficulties meshing a volum with two of its faces having 2d BL. Indeed, i have to blocks, one should be mesehd with two times less cells than the other. For the transition, i use a BL (with 3 rows). I mesh then the face, Gambit tells me that the face is meshed with poor quality and once i sweep it to obtain the volum, then i have chaotic lines growing randomly.
How can i extend the BL to the volum i want to obtain?

Thank you in advance
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Old   June 12, 2012, 04:59
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you shouldn't use Bl in this way.
This is not a mesh-schema.
Are you enforced to have upper and lower surfaces with different densities?
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Old   June 12, 2012, 05:28
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Yes, i expose the problem to you. I am a stydying water dambreak. To accelerate computations, i am dividing my domain to several zones so that each processor treats a zone.
Concretly, there is no need to mesh all the zones the same way because it is time onsuming. Only those who contain the water/ air interface should be treated carefully.
This is why i use 2 different densities.

I already tried with a uniform mesh everywhere but results are not concluding. there is strong diffusion of the interface.

BL are not the solution according to you? How could i do then please?

Thank you in advance
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Old   June 12, 2012, 05:33
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I said that you cannot use BL as a meshing-schema.
In your case: delete the volume mesh from volume1, and delete all BL.
Then the rectangle, you "meshed" with a BL, you can for example mesh it with Quad-Pave schema.
Add some nodes on edges 14 and 16 and mesh the surface with Quad-Pave
Then Mesh volume 1. Gambit should choose automatically Hex-Cooper meshing-schema.
That's it.
Now you can add BL on your walls, if needed
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Old   June 12, 2012, 06:03
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That you for your advice. I ll see how the code deal with such a mesh. BL are no more necessary now.

But if i want to have only a quad/hex mesh everywhere. Is it possible to do so? Since my geometry is not complex at all.
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Old   June 12, 2012, 06:39
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no you cannot since lower and upper surfaces don't have same density
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Old   June 12, 2012, 07:00
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Yes you are right. Could tou please look at what i have recently tried with BL and face meshing.

Now when i sweep the faces i have the volum that is meshed properly. The problem is the small space i have from the edge of my face where i have the BL.

In fact we are told that it is possible to attain a quad/hex mesh everywhere. this is why i am desperately trying to find a solution.

Thanks for your help
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Old   June 12, 2012, 07:57
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you also tried to "mesh" a face with a BL.
It is not ok.
Why don't you want to use Quad-Pave?
it is also Hexa elements, but unstructured
Else you have the possibility to work with interfaces
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Old   June 12, 2012, 13:37
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BL are definitely not meshing schemes as you said first. Are they only means for transitions? Can they be used in another way?

You menshioned interfaces as an alterative. What do you mean by that? Sorry i do not have much knoledge yet about gambit.
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Old   June 13, 2012, 00:57
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BL are used to treat turbulence transition at walls
http://en.wikipedia.org/wiki/Law_of_the_wall
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Old   June 26, 2012, 08:44
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Hello!

I managed to obtain unstructured hexa map mesh instead without using hexa pave mesh (cf dem using BL). Now i would like to do the same thing but for the faces in the (oxz) plane. When i try to do so (cf. dem2) once i try meshing the volume with hex cooper scheme i have errors concerning the choice of source faces. I keep having the same error message eventhough i change the source faces. After trying many times, i think it is impossible to mesh the volume with the configurations i have settled.

I know it is possible to use pave or tri mesh. But i would like tu use haxa/map or submap mesh.

For example in the picture i joined(dem), the density of mesh in face.1 is 3 times higher than the one in face.2 because i use 1:3 Bl then mesh the face in Y direction. Then i sweep it in the z-direction but this generates a uniform mesh according direction z in both volums. In fact i want a volum mesh where the whole volum 2 have 3 times less cells than volum1 without using pave or tree schemes.
Does anybody have an idea? Thanks in advance
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File Type: zip dem2.zip (1.5 KB, 0 views)
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Old   June 27, 2012, 00:37
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If you want Hexa mesh then you need to use interfaces
>disconnect face 6
>Mesh volume2 with your desired element size
>Mesh volume1 with also your desired element size
If you leave your mesh like that, then in Fluent you will have walls between your 2 volumes, because they are disconnected.
For the reconnection, you will use interpolation (interface)
>define face6 as interface1
>define face13 as interface2
faces6 & 13 are superposed

Export your mesh, then in fluent define the grid interfaces by choosing both interfaces you defined in Gambit
Sans titre.png
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Old   June 27, 2012, 02:44
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Hello!
I am not using fluent. The code i am using does not allow using interfaces otherwise it would have been much simple i guess, faces and edges must be connectedin my case. Thank you for your answer

Last edited by nore; June 27, 2012 at 04:31.
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Old   June 27, 2012, 02:48
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If you don't want Pave schema or tetrahedral Mesh and you cannot use interfaces, then I am afraid you cannot handle your problem (that's my opinion).
But maybe someone else has the key...
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