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multiply then translate/totate a mesh ?

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Old   May 11, 2016, 05:33
Default multiply then translate/totate a mesh ?
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Hi all,

I'm new in CFD, the only mesher I've ever used for the moment is blockMesh.
I've to mesh a case (posted on photo below) which is a kind of 9 repetition of a same shape (a pipe).


Here are my questions :

FIRST
I've already mesh a part of the geometry (one of the 9 pipes) with blockMesh. There's a photo below. I would like to know if there's a possibility with OpenFoam to copy/translate/rotate this mesh in order to make my entire mesh ?? (Because my external faces are squares, the merge should be possible...)

SECOND
Do you know if Gmsh can make 3d boudary layers in order to mesh my case ? I would like to make boundary layers on pipes then a tetrahedral on the rest of the domain.

Thank you for your help
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File Type: png pipe.png (103.9 KB, 6 views)
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Old   May 11, 2016, 05:51
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1. Copy, transformPoints, merge or stitch meshes.
2. Google says yes. I'd suggest checking out snappyHexMesh if you have an STL of your pipes.
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Old   May 11, 2016, 07:46
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Thank you very much for your help akidess,

1. Sorry but could you be more specific on that ? I see that transformPoint will be able to move my original mesh. But I'm don't know on how to proceed in order to copy my original mesh then merge the two final mesh in order to make a bigger one...

Here is what I understand:
- 1/ run my original blockMeshdict (to make my original little mesh)
- 2/ then, made a copy of all my directory polymesh (to copy my little mesh)
- 3/ do the operation of translation/rotation thanks to transformPoint on the copy.
- 4/ Then do an operation that will merge the two mesh (original and copy) merging the two directory polymesh.

If it's what you were telling me, how would I do the 4/ ?

2. Concerning Gmsh I haven't seen many things on google concerning 3D boundary layer while that's a basic I think. That's why I prefer asking...
Concerning happyhexMesh, I've heard that it could present some problem with big mesh (upper than 3M cell... :s )

Last edited by adrieno; May 11, 2016 at 09:20.
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Old   May 11, 2016, 09:15
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You got it. The final step 4 is using the utilities stitchMesh or mergeMeshes. I'm not sure off the top of my head which one is the correct one to use. Perhaps both (merge, then stitch).

I use snappyHexMesh all the time for meshes up to 20 million cells or so. It does require quite a bit of RAM though.
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Old   May 11, 2016, 09:19
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Well, thank you ! You convince me to go on snappy then !
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Old   May 12, 2016, 08:28
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Hi akidess,

I'm trying to mesh my case using gmsh (to generate the geometry in .stl) and snappy.

I found many tutorials so that's great but I'm wondering about a specification of my case. Maybe you have the answer:

The fact is that my geometry is "touching" ( /going out) the domain of control.
So how do I do for the box control ?

I mean:

FIRST do I need :
1/ to define my box control in my geometry .stl (like you can see on the picture below). In that way, the box in the .stl define the volume of the fluid (volume in the square whithout the pipe).

2/ to define a cube of the same size (of my box in the .stl) in my blockMesh for the very first mesh hex

=> By this way, I'm afraid I can't define differently the box boundaries and the pipe boundaries...


SECOND :
- I just need to define the pipes in my .stl then define the box control in blockmeshDict.

=> By this way I'm afraid there will be problems of junction between the faces of the box and the extremity of the pipe. I mean, I'm afraid it will mesh inside the pipes or do something bad on the extremities...

Is it possible to make a geometry .stl larger than the box control in the blockMeshDict ? (Because if it's possible, I would just have to make my pipes a bit longer doesn't I ?)

Any suggestions would be welcomed !
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Old   May 12, 2016, 08:34
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aaaa, I'm not clear sorry...

In a simple way, I don't know how to handle the intersections between my geometry and the box control...
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Old   May 12, 2016, 09:51
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The second way. Make the pipes larger than the control volume you define in your blockMeshDict. Everything outside of your starting block mesh is ignored.
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