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-   -   create STL file with zero thickness plates with surfaceMeshTriangulate (http://www.cfd-online.com/Forums/openfoam-meshing-snappyhexmesh/94749-create-stl-file-zero-thickness-plates-surfacemeshtriangulate.html)

TimG November 24, 2011 06:53

create STL file with zero thickness plates with surfaceMeshTriangulate
 
Hi,

i am trying to generate an STL file from a Fluent/Gambit Mesh (*.msh) with surfaceMeshTriangulate for mesh generation with SnappyHexMesh . The surfacemesh contains plates with zero thickness (like a baffle), that are not connected to a wall on each side. After the creation of the STL file with surfaceMeshTriangulate, these plates have disappeared. I believe that the reason is that the STL Format is used to describe Volumes and subsequently the plates are ignored. Is that true? Is there a way to keep these plates?

Additionally, if i add a plate by hand, snappyHexMesh does not snap the STL correctly. At the edges that are not connected to a Wall, the Mesh looks badly deformed. Why is that?

Kind regards
Tim

matteoL February 9, 2012 05:10

Hello Tim,
I am trying to use snappyHExMesh on a zero thickness geometry like you did and indeeed the result is not very satisfactory.. The edges of the surface are not snapped at all..

Have you managed to find a way to resolve the issue?

Thanks,matteo

TimG February 9, 2012 08:39

Hi Matteo,


i did not find a way. But i did some research on the STL format. It is designed for the representation of volumes, and since a zero thickness plate is not a volume, it might be a reason why the "surface mesh triangulate" tool can't create STL Files from other geometry files that include zero thickness plates.

It is possible to create stl files containing zero thickness parts with other CAD Tools and mesh them with snappyHexMesh. But if you take a look at the windshield (a 2D geometry) of the motorcycle in the motorcycle tutorial, you will find that the upper edge is snapped very poor. I believe snappyHexMesh is not capable to mesh zero thickness geometries correctly for now.
If anyone knows how to mesh zero thickness geometries with snappyHexMesh, feel free to reply.


Kind regards,
Tim

sail February 9, 2012 11:47

I have to confirm the TimG's word about it. it is really hard if not impossible to use a 0 thinckness stl file.

to overcome this i usually have two options:

1) if my cell number permit, i use a solid with very low thickness and use it normally. take keep in mind that you can scale the mesh after the sHM phase, so it is possible, if your geometry permit, to have s sensible thickness in the z dimension, mesh it, and then scale the mesh to keep it as low as possible. you can find examples (but applied to 3d body) in the wigley hull tutorial (LTSInetrFoam

2) use external meshing sw.

good luck.


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