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# Curved pipe thin wall mesh

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### Curved pipe thin wall mesh

Posted by Kirill St at March 04. 2013

Hi.

I have a problem to get a good result of a modal analysis (code aster).

I solved few well known problems, and got very good results but in my case I am getting bad one.

I mesh the pipe with automatic hexaherdalization mesh.... this is thin wall "U" curved pipe.

How do I solve this problem?

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### Re: Curved pipe thin wall mesh

Posted by Kirill St at March 06. 2013

The question is how can I mesh the wall of the pipe with maximum number of cells

Thanks

### Re: Curved pipe thin wall mesh

Posted by William Tougeron at March 06. 2013

Hello,

If the geometry is as simple as in your screenshot, you can maybe rebuild it in Salome so as to create a blocking and mesh it.

Enclosed is a picture summing up what I mean.

The purpose is to create the section (for example with two disks and a cut operation), then to extrude it along a wire composed of three edges (this is only an example).

Then, you can partition this extrusion with planes so as to have six different blocks, and to apply on the final partition a hexahedral mesh.

The only one important precaution to take is to put the vertexes inside the section in the symmetry plane of the desired geometry, like in the picture. You can see theses vertexes after exploding the section (New Entity > Explode). If they are not laying in the symmetry plane, you will have to rotate the section before extruding it. Else, some blocks will have more than twelve edges in your final compound and the meshing step will fail.

Best regards,

William

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### Re: Curved pipe thin wall mesh

Posted by Kirill St at March 06. 2013

Thank you William.

I would like to know how to define the number of cells in of the wall thickness.

If you can send it in step-by-step way it would be great. (I am importing the geometry in STEP file)

### Re: Curved pipe thin wall mesh

Posted by William Tougeron at March 06. 2013

Hello,

The problem of importing a STEP file is that there is a big chance that this geometry is not compatible with hexahedral meshing in Salome (unless you use the new Hexablock module, but I have no experience with this tool). But if you can check your final partition with Measure > Check Compound of Blocks without getting any error, it's OK.

About the mesh, the first step is to create a "global" mesh. That is, create a mesh on your pipe with Mesh > Create Mesh and apply on it (for example) an Automatic Hexahedralization (which is available after clicking on the Assign a set of hypotheses button at the bottom of the dialogue box). Doing this, you will set "global" algorithms+hypothesis which will by applied on each of the edges, faces, and solids of your geometry. Now if you want to setup "local" parameters (for example only throught the wall thickness), you will need to create sub-meshes.

To do so, you can come back to the Geometry module and use on your geometry Operations > Blocks > Propagate to create all the groups of edges which must have the same number of nodes in the mesh. You can then look for the one on which you want to define a specific discretization. (In the enclosed picture, showing the different groups I get, the good one is in red.)

Then, in the Mesh module, you can click on your mesh (eg. Mesh_1), then on Mesh > Create Sub-mesh, puting in the Geometry field the group of edges in question. Then, I recommend to use the 1D algorithm Wire Discretisation, with a hypothesis of type Nb. Segments, as in the picture. (You must click on the blue pinion at the right of the Hypothesis field to create a new hypothesis.)

Once your sub-mesh is configured, you can recompute your mesh and it should be OK.

Best regards,

William

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