Blade meshing

Hi all,
I have just started to learn how to mesh a solid. I am a newbie in FEM.

I was wondering if someone could help me in getting the windmill's blade I am working on meshed.

I manage to get it meshed with tetrahedrons. Yet I would like to be able to get it meshed with hexahedra.

1)I exploded the stp model in faces and edges;
2)I got the solid meshed with tetrahedrons;
3) I defined sub-meshes on faces (quadrangles) and edges of the solid with a fixed number of points (50)
4) I tried (wrongly as a matter of fact) performing the mesh of the solid again but this time using the existent surfaces and edges;
5) I get the error: wrong number of subshapes of a block.

I would be grateful if anyone could give me some hint, or address me, to some tutorial or document to put some light on my misunderstanding.

Thanks,
Pier<br /><br />Post edited by: Pierpaolo, at: 2009/03/23 21:20

I put a snapshot of the blade here:

pier.unirc.eu/cestino/mesh.jpg

and the hdf file here:

pier.unirc.eu/cestino/blade.hdf

Thanks,
Pier

ciao Pierpaolo,

a solid to be hexmeshable must have congruent 2D-meshes on its bottom and top faces. These are your faces &quot;root&quot; and &quot;tip&quot;. They are not congruent, because have different nb of elm. To make them congruent use &quot;2D-projection&quot; as meshing algorithm for one of them to make it slaved to the other face. Before using &quot;2D-projection&quot; You must also use &quot;1-projection&quot; as meshing algorithm for all edges of the slaved surface to make them slaved to the corresponding edges of the master surfaces.

I suppose that it is also necessary that Your body consists of only one length segment. This means only the outer or only the inner length segment of Your blade, close at their bottom and top with a face. So You can create 1) either 2 HEX-meshes connecting them in Code-Aster with a glued contact, or 2) 2 HEX-meshes with congruent surface meshes in their contact surf, compounding theses meshes one mesh and merging the nodes, or 3) You start with only one segment containing the full length of the wing.

In either case, if You have problems of get Your pretty hex-mesh, can You post the result here again (problem or hex-mesh)?

good luck
Johannes Ackva

______________________________________________________________________
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Dr.-Ing. Johannes Ackva
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www.code-aster.de

Hallo Johannes,
thank you very much for your reply.

&lt; a solid to be hexmeshable must have congruent 2D-meshes on its bottom and top faces. These are your faces &quot;root&quot; and &quot;tip&quot;.

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... well why didn't I notice that? Thank you for opening my eyes.

&lt;

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So You can create 1) either 2 HEX-meshes connecting them in Code-Aster with a glued contact, or 2) 2 HEX-meshes with congruent surface meshes in their contact surf, compounding theses meshes one mesh and merging the nodes, or 3) You start with only one segment containing the full length of the wing.&gt;

I chose to build one compound starting from the IN and OUT compounds but now I am stuck. How do I get the internal mesh? Any other hint would be greatly appreciated.

&lt;In either case, if You have problems of get Your pretty hex-mesh, can You post the result here again (problem or hex-mesh)?&gt;

Here again is the link to the hdf file:

pier.unirc.eu/cestino/blade_compound.hdf.gz

Danke schoen,
Pier<br /><br />Post edited by: Pierpaolo, at: 2009/03/25 22:39

Ciao Pierpaolo,
the mesh is still not done, but I have some remarks to contribute to our discussion and also a kind of preliminary mesh attached.

1) In Your .hdf-file You have only 2D-meshs and so also the Compounded meshed (I can't edit and can't look onto them) must be composed of 2D-meshs. But what is needed is a 3D-mesh. A 3D-mesh must always be referenced to a 3D-geometry. When You need submeshes (and You need them, because You have to apply special meshing algorithms to the Top- and Bottom-face) these submeshes must reference to subshapes (faces) of the 3D-geometry. This means, the 3D-geometry must be exploded. When You explode it, the faces must fulfil a certain topology: Top- and Bot-face. And lateral faces. I don't find it in the Salo-doc, but from a meshing fail I conclude, that Salome's HEX-mesher expects 4 lateral faces (meshers in other Preprozessors can handle with diffenent numbers of lateral faces.

2) the original 3D-geometry (.stp) consists of 2 length segments (inner and outer part of the wing). To make things easy one can start mehing only one part. a) exploding the original 3D-geometry b) creating a Top-face (from a wire) c) creating a shell representing the hull d) creating the solid from the hull, e) exploding the solid in Top-, Bot- and Lateral-faces as needed for the Hex-mesher. Unfortunally there are only 2 lateral faces. f) in MESH-modul: creating the 3D-mesh referencing the solid of step d), g) creating 2D-submeshes referencing Top- and Bot-.

3) I attach my .hdf-file with mesh. As You see 3D-meshing fails, because nb of lateral-faces unequal 4.

4) What now? Perhaps one could try to slice the 2 lat-faces along their length, to have 4 lat-faces. Top- and bot-faces should be recreated from edges and wires because actually they have only 2 edges (must have 4).

5) When 3D-meshing of the inner wing part is done, the same work for the outer part can be done. Then the 2 3D-meshes can be compounded to a new 3D-mesh. The nodes in the contact face may or may not coincide. If yes, they can be merged (in Salome). If no one can use Code-Asters glue contact to glue the 2 3D-parts (which are both contained in ONE mesh) together.

6) Other approach: If You create compounded lateral faces, it seems to me (I m not shure if there is another possiblity) that when exploding the solid (=solid of complete wing), it explodes always into the original faces, so the topology necessary for HEX-meshing cannot be obtained. If one don't want to make a compound mesh, it is necessary to import another step geometry which has only 1 length segment.

7) I too learn a lot from Your example, so when You do a next step, I could again have a look onto Your next result. Sorry when I write or repeat some things which may be You know already, writing helps just even me to make me things clearer.

BEst regards, Johannes Ackva<br /><br />Post edited by: johannes ackva, at: 2009/03/27 17:10