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Block decomposition mesh - Ogrid nested inside an Hgrid

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Block decomposition mesh - Ogrid nested inside an Hgrid

Posted by Susan Tully at April 24. 2013

Hello,

I am trying to create a mesh similar to that shown in the attached jpeg - a small square hGrid region nested inside an oGrid region, which in turn sits inside a larger, rectangular hGrid region. Then the whole thing extuded out.

I know I have to use block decomposition for this since I require 4-sided faces. So I built a model as shown in the right image, made up of the different 4-sided regions. When I apply a hex mesh to this I get the different meshing structures I require in each block which is great, but the mesh does not connect well across the boundaries between the ogrid blocks and larger hGrid blocks. I guess because I have meshed each block as a separate entity. 

So my question is this - how do I mesh the whole thing as one so that my mesh connects well across boundaries. From what I have read I think I have to use submeshes setting restrictions on how the mesh should behave across block interfaces. But when I try to do this it only seems to change what is happening on one side or the other.

I built my geometry in Ansys since I am more familiar with that and for CFX meshing I can define my blocks as regions of influence to the overall structure when meshing to do what I desire. Can I do a similar thing in Salome? Do I need to explicitly tell the program that my structer is a composite structure made up of the individual blocks for this to work?

Any help would be appreciated, sorry if this is too simple/vague a question I am asking!

Best regards

Susan

 

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Re: Block decomposition mesh - Ogrid nested inside an Hgrid

Posted by Saint Michael at April 24. 2013

Hi Susan

Can you modify your geometry as shown in the attached picture (actually only one of 4 similar changes needed is shown)? Then you life would be much easer :)

St.Michael

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Re: Block decomposition mesh - Ogrid nested inside an Hgrid

Posted by Susan Tully at April 24. 2013

Hello, firstly thanks for getting back to me. I did think about doing the geometry that way, but as I was after a very structured oGrid in the disc region I thought this would give me non radial lines? I will give it a try though and see what I get. I may end up using an unstructured mesh in the regions outside the disk too since my rectangular domain is so tight around the disk and Im getting such stretched elements.

Can you shed any light on getting the elements to match up across block edges? Ive since learnt that thats called 'hanging nodes', I learn more by the minute!

thanks

Susan

Re: Block decomposition mesh - Ogrid nested inside an Hgrid

Posted by Saint Michael at April 24. 2013

In SALOME, to get a conformal mesh over edges of faces, one needs to make faces share their edges. The same for solids and their faces. For this, Partition operation is used. So, if you use all your faces, or solids, as Objects parameter of Partition, then all neighbor faces will share their boundaries.

After that, if you had your geometry as I advised, you would get a desired mesh the same way as you already did.

St.Michael

Re: Block decomposition mesh - Ogrid nested inside an Hgrid

Posted by Susan Tully at April 25. 2013

Great thanks, using the partition function worked great. Thank you for your help, it was much appreciated! :)

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