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How to create patch after snappyHexMesh

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Old   August 8, 2008, 09:00
Default Hi, snappyHexMesh is a grea
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Pei-Ying Hsieh
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Hi,

snappyHexMesh is a great tool. Save me lots of time creating meshes. However, I do run into a problem with some situations. I am wondering if anyone has encounter the same isssue and have ways to resolve it.

As seen in the picture, I want to create a mesh "inside" the cup. I have stl file of the geometry. So, I create a simple block to contain the cup. After snappyHexMesh, I got the mesh inside the cup. But, at the point, there is only 1 patch, that is the wall of the whole geometry. I need to separate this 1 patch into: inlet, wall1, wall2, and atmospheric. How to achieve this? Sometimes, the patch I am interested in may be curved surfaces, so that patch is not always flat. Suggestions will be highly appreciated.

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Old   August 8, 2008, 09:01
Default press send too fast before add
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press send too fast before adding the picture.

\image{cup};

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Old   August 8, 2008, 09:02
Default OK, let me try this again.
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OK, let me try this again.


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Old   August 8, 2008, 10:08
Default We do this by either: 1. Usin
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Eugene de Villiers
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We do this by either:
1. Using separate STL surfaces for each region
2. Using STL or NASTRAN surfaces with multiple internal regions.

You can also get additional patches from the original blockMesh by intersecting the surface geometry with the block boundary.
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Old   August 8, 2008, 11:59
Default Hi, Eugene, Thanks. I thin
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Pei-Ying Hsieh
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Hi, Eugene,

Thanks. I think I understand approach #1, but, can you explain approach #2? It is not clear to me what STL/Nastran surfaces with multiple internal regions means. How to create that?

Pei

PS: I use SolidWorks to create geometries.
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Old   August 10, 2008, 16:28
Default Thanks Eugene, I was not aw
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Thanks Eugene,

I was not aware that the file may also be in Nastran format? This is quite helpful. I am also wondering how you make snappyhexmesh to use multiple stl-Files at one time? Is it sufficant to place them into the trisurface dictionary?

Thanks.
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Old   August 11, 2008, 06:12
Default Hi Bastil, We use CATIA/ANS
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Eugene de Villiers
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Hi Bastil,

We use CATIA/ANSA to make surfaces and these tools provides the capability of exporting multi-regioned surfaces. I have never personally used solidWorks, so I cannot comment on that.

To use multiple surfaces just add more surfaces to the geometry and refinementSurfaces sections of the snappyHexMesh dict. Of course they need to be in the triSurface directory as well.
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Old   August 11, 2008, 08:10
Default Hi, Eugene, My understandin
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Pei-Ying Hsieh
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Hi, Eugene,

My understanding is that, the geometry has to "close". For example, say, a cube. It has 6 sides, top, bottom, left, right, front, back. When exporting to STL, the STL file consists of several triangulates, and we no longer have patch name, such as top/bottom/front/back/left/right associate with the STL file. In snappyHexMesh, all 6 surfaces got lumpped into 1 surface, say called cubeWall. Is ther a way to keep the the original patch names in STL?

In SolidWorks, it can select a surface, split it into two surfaces (can be any shape). But, once exporting to STL, there is no name assocates with the surface. I can export specific patch surface to STL, but, can it be used in snappyHexMesh?

Pei
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Old   August 11, 2008, 11:40
Default Like I said, I don't know soli
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Eugene de Villiers
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Like I said, I don't know solidWorks. But in our regioned STL files regions look something like this:

solid top
'triangle stuff'
endsolid top
solid bottom
'more triangle stuff'
endsolid bottom
etc.

I don't think this kind of regioning is a standard STL feature. However, NASTRAN does support regions by default.
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Old   August 11, 2008, 11:43
Default Eugene, thanks once more. I
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Eugene,

thanks once more. I also do not use SolidWorks. I guess from CATIA your way is multi-part stl? What about ANSA? I do not know ANSA, do you use stl there, too? The other question was if nastran-Format is possible, too. This seems to be the case.

Regards
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Old   August 12, 2008, 05:13
Default These days we mostly use NASTR
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These days we mostly use NASTRAN with and without multi-regions.
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Old   September 1, 2008, 11:53
Default Hi all, I have problems exp
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Hi all,

I have problems exporting multi-region Nastran files from Hypermesh. It seems HM has different Nastan formats (long, CFD, standard,..) OF only reads "standard" option. However, regions are not discovered and I have some warnings about unrecognised NASTRAN-commands. I see HM has written regions into the file, but obviously the format is wrong. What does it have to look like?

Regards.
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Old   September 13, 2008, 13:57
Default Hey all, What I've found to w
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Hey all,
What I've found to work in solidwork is to generate individual solid bodies for each patch that you'd like to generate, then save them as individual, ASCII .stl files (not allowing solidworks to translate them to positive space, so you insure relative positioning is correct), then concatenate the .stl files, and apply the snappyHexMesh to that.

This worked OK for me, and actually sort of makes sense with the way that my solidworks assemblies work.
Thanks,
D
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Old   September 22, 2008, 17:41
Default Hi, Eugene, I am wondering
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Pei-Ying Hsieh
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Hi, Eugene,

I am wondering if you can post a complete multi-part stl (simple geometries will do). I am wondering if I can edit my stl file from SolidWorks to try out snappyHexMesh.

thanks!

Pei
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Old   September 23, 2008, 04:05
Default Pei, you can have a look at
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Pei,

you can have a look at the Motorbike Tutorial. This is exactly what you are looking for.
However, I would be interested in a example Nastran-File from a simple geometry that works (remain both patches and patch-names). I am struggeling with the Hypermesh-Export so far. Thanks.

Regards Basti
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Old   November 25, 2008, 03:45
Default Hey all just an FYI.. If yo
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Hey all just an FYI..

If you are using Salome to create your geometry. (CAElinux is a live dvd with salome installed if you want to try it out)

You have the option to explode your geometry into faces give them names like vel_inlet press_outlet etc.. and export each face to their own .stl file.

exporting to an ASCII .stl will allow you to edit the text and give each solid names.

You can then use these multiple files in snappyHexMesh (haven't tried this so don't know if it handles multiple files).

The other way is to combine the face .stl files into a fully defined solid by appending each separate .stl file into one by for example using a command like this. (assuming it is a cylinder)

cat inlet.stl >> assembly.stl
cat outlet.stl >> assembly.stl
cat walls.stl >> assembly.stl

Then you have a fully defined solid and provided you have given the three solids names these will be added to your final boundaries file and you can specify the inlet/oulet conditions as usual after running snappyHexMesh.

Hope this helps anyone.

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Old   December 12, 2008, 05:39
Default Hi, i'm trying to create a
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Hi,

i'm trying to create a mesh inside a geometry with the snappyHexMesh utility.
The mesh seems ok but i can get the patch i want. I have different stl surfaces and i would like to have a patch for each of them. However, I just have the patchs related to my initial background hex mesh and one, corresponding to te complete geometry...

Is using different stl surfaces not sufficient?

Thank you

Bastien
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Old   December 12, 2008, 06:19
Default Last thing, what should i d
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Bastien Holbek
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Last thing,

what should i do with the boundaries of my background hex mesh. I don't simulate anything outside the geometry. Put empty for example?

Thank you

Bastien
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Old   December 12, 2008, 08:28
Default It's enough that you put all y
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It's enough that you put all your patches in one STL file. At the end you will have different patches in your mesh, where the mesh has been built. Using multiple stl files is fine as well. Check that you saved your STL as ascii, as in binary files patch names are not written.

I cannot understand your last question. If you need to mesh inside your geometry, you should not have any mesh between it and your background mesh, as your keep point must be inside.
If you have a mesh on both sides, it means that you have a hole in your geometry.

Hope this helps,
Francesco
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Old   December 12, 2008, 12:37
Default Hi, Thank you for your answ
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Bastien Holbek
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Hi,

Thank you for your answer.
actually, i don't have mesh outside my geometry, it's ok. However, snappyHexMesh creates a defaultFaces patch, which comes from my background hex mesh, i think.
Is it normal?

Thanks

Eric
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