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Pure hex mesh with snappy

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Old   April 29, 2009, 03:15
Default Pure hex mesh with snappy
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Alf Melchior
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Hi!

I am just trying to generate a pure hex mesh with snappyHexMesh without any degenerated elements like wedges or alike. Is this possible at all with snappy? I tried playing around with some of the parameters of meshQualityControls (e.g. minDeterminant) but I get either at least some of the unwanted elements or a staircase like surface.

Thus my question: Is it possible to generate a pure hex mesh - and if it is which parameters to select (for example for the motorbike test case).

Thanks

Alf
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Old   October 1, 2009, 10:20
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Philip Cardiff
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Hi,

You could try IA-FEMesh:
http://www.ccad.uiowa.edu/mimx/IA-FEMesh/

It produces purely hex mesh from STL surfaces.

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Old   October 6, 2009, 05:19
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Hi Philip,

thanks for you answer. I tried it and it looks that it works quite well - even if the handling is somewhat unusual.

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Old   January 21, 2011, 19:08
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Can it generate Unstructured HexaHedral meshes.?
And how would your compare it with snappyHexmesh?
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Old   January 24, 2011, 06:07
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Hi owayz,


All hexahedral meshes are structured.

That's why they are more difficult (and require much more user input) to create than tetrahedral meshes.

If you geometry is simple (or made up of simple shapes) then blockMesh will create a structured hexahedral mesh.

If you have a complex geometry and you have the STL surface file, then IA-FEMESH can create a pure structured hexahedral mesh.
snappyHexMesh can create a structured hexahedral mesh with polyhedral near the surface of the STL.
There are also many other meshing software that can do similar things like gambit, ICEM etc.

There might be some software that can automatically create a structured hexahedral mesh (like moceon cheetah) but I am not familiar with it.


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Old   February 14, 2011, 08:03
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Hi Phillip,
Thanks very much for your reply. But I would really like to create a pure Hexahedral mesh with snappyhexmesh. So my question is still the same:
"Can it generate pure hexahedral meshes?" A "yes" or "no" might save me alot of effort and time.
And if it can and someone call tell how is it possible, I mean which parameters to change then it would be like heaven on earth for me.
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Old   February 14, 2011, 08:27
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Philip Cardiff
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owayz,

as far as I know (please correct me if I am wrong), snappyHexMesh cannot create a purely hexahedral mesh that is snapped to a surface,
it always puts general polyhedral cells near the stl surface during the snapping phase.

It can produce a pure hexahedral mesh that has not been snapped to the STL surface but this leaves your mesh surface as castellated so it might not be very useful.

Hopefully this helps,
Philip
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Old   February 14, 2011, 11:06
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Ya Thanks for the reply. I just relized that. Actually i was trying to generate the pure Hexahedralmesh with snappy but it turns out to be that a pure hexahedral mesh won't be snapped. In simple words snappy needs refinement to be done for snapping and during refinement its produces polyhedral cells. So there is no easy way around the solution. But I still would love to hear anyother aproach if there is possible.
Regards
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Old   February 14, 2011, 11:21
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Awais,

You could check out IA-FEMesh (http://www.ccad.uiowa.edu/mimx/IA-FEMesh/), it can produce pure hexahedral meshes from STL surface, albeit with considerable input from the user.
Also it can be awkward getting the mesh into OpenFOAM, but it is free.

There are commercial meshing programs like ICEM that will produce purely hex meshes.

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Old   February 14, 2011, 11:36
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Yes ICEM is a good option. But let us try to get things done inexpensively.
Thanks for your advise. I will surely give IA FEMESH a try.

Regards,
Awais Ali
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Old   February 14, 2011, 18:16
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Quote:
Originally Posted by owayz View Post
Ya Thanks for the reply. I just relized that. Actually i was trying to generate the pure Hexahedralmesh with snappy but it turns out to be that a pure hexahedral mesh won't be snapped. In simple words snappy needs refinement to be done for snapping and during refinement its produces polyhedral cells. So there is no easy way around the solution. But I still would love to hear anyother aproach if there is possible.
Regards
Awais Ali

Owayz , i have this grid generation book:

http://www.amazon.com/Handbook-Grid-.../dp/0849326877

This book says that it is possible to snap to pure hexa meshes. It is difficult but possible. This book explains also how it is done.

As for snappyhexmesh of openFOAM is concerned it may not be possible.

(i am reading that book because i want to write similar grid generator myself and was interested in how to generate high quality meshes.)
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Old   January 25, 2013, 03:43
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Timo Kulju
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Hi!
I did a mesh with purely hex and polyhedral elements by setting minDeterminant to 1. My geometry is a bit simpler than motorbike, but anyway it was possible. Maybe with fine surface refinement, and using OpenFOAM-2.1.x, it could be done.

- Timo
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Old   February 14, 2013, 06:52
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Hello everybody,

When I mesh a domain around a geometry like a boat, it seems that the generated mesh consists of tetrahedral elements(not hexahedral). I want to know how to produce a hexahedral mesh?

Any suggestion is welcome.

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Ali
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Old   February 14, 2013, 12:15
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Hi,

I think you had a look at your mesh with paraview and slices or clips?
You have to use the filters for a correct view of the cells in paraview.

ExtractCellsByRegion

or you can calulate an new array with cooridnateX and have a look at that with treshhold.

Hope that is helpful

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Old   February 15, 2013, 08:15
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Dear Tobias,
Thanks for the reply. I used ExtractCellsByRegion filter and attached a screenshot of my mesh in the central region. It looks like that the mesh contains polyhedral elements.(both 5 & 6) Am I wrong?

Cheers,
Ali
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Old   February 15, 2013, 10:30
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Hi,

you have to choose both option on the left side.
After that you have to move your slice to a good position to get a good result.
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Old   February 17, 2013, 14:52
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Ali Khalifesoltani
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Hi again,
I used ExtractCellsByRegion filter, but still the cells looks like both 5 & 6 hedrals. I would be grateful if you help me on this!

regards
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Old   February 17, 2013, 15:24
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Greetings to all!

@Ali: When you run paraFoam, you're shown the "Object Inspector", in the lower left part of the ParaView window, which provides one of the following options:
  • If you are using the official plug-in, namely using the file extension ".OpenFOAM", then turn on the "Use VTKPolyhedron" option.
  • If you are using the internal plug-in, namely using the file extension ".foam", then turn off the "Decompose polyhedra" option.
Best regards,
Bruno
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