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-   -   [ICEM] Cut existing Mesh in order to use symmetry (http://www.cfd-online.com/Forums/ansys-meshing/80711-cut-existing-mesh-order-use-symmetry.html)

camoesas October 4, 2010 11:05

Cut existing Mesh in order to use symmetry
 
Hello Everybody,

I already have a mesh for my CFX-Problem. Now I want to cut it in two pieces in Order to reduce the cell numbers and to utilize the symmetry. Is there a function in ICEM for this? Or anything similar which leads to the same result.
I have considered "Cut Plane". But "Cut Plane" ist just usefull vor visualization.

Any ideas appreciated

Thanks


Simon

camoesas October 5, 2010 09:35

Push:

Ok, maybe some more information: First I am using V12.1

I have a mesh of an radial journal bearing. I want to use the symmetry and cut the existing mesh into halves.
These are my ideas so far, but nothing really worked:

- as I said 'Cut Plane'
- Split the Blocks manually and assign the new faces to a new part 'symmetry'. didn't work: Ive already failed splitting the blocks along a surface

- do I have to start with manipulating the geometry? But then will I have to remake all the blocking again?


(Because of the rotation 2D is not an option)

Thanks Simon

PSYMN October 5, 2010 17:29

Options...
 
You can do this at the blocking level or the mesh level...

Either way, it may be handy to start by adding a symmetry plane to the geometry.

Geometry portion; Create a surface in the right plane (from 4 corners or what ever method you want). Create intersection curves between the plane and the geometry... Trim if you want, but it is not required.

Blocking Option; (my preference) Split the blocking so you have an edge aligned with the symmetry plane... You may already have an edge in this location. Associate the edge with the symmetry plane intersection curves. Then just delete all the blocks on one side... The exposed symmetry plane faces will automatically project to the symmetry plane.

Edit Mesh Option; If your mesh does happen to line up with where your symmetry plane is and you don't have the blocking handy, you may want to do it at the mesh level. Just delete half the mesh in the model (volume mesh and surface mesh). Then run the mesh checks. It will find uncovered faces where your symmetry plane should be. Choose "Fix" and it will offer you a list of parts, pick or type in your symmetry part. This will put shell elements in the Symmetry part to cover the exposed volume. Then go to Edit Mesh => Repair => Build Mesh Topology. This will use feature angle to extract and associate the feature curve along the symmetry intersection plane...

Have fun...

camoesas October 6, 2010 02:15

HI Simon,

thanks for your suggestions, Ill try the 'blocking' solution first and will report my progress!

Simon

camoesas October 6, 2010 05:46

Hello,

Now I have trimmed the whole Geometry. Removed the O-Grid. Splitted the Blocks along the symmetry plane and deleted the obsolete blocks.

I have inserted a new block, but the new block is green all the other blocks are purple. Does this mean anything?
Not that I am really concerned but sometimes the colours have meanings and If you dont care you get problems later...

Simon

dst October 6, 2010 07:41

Hello Simon,

if I understood your actions correct, you have inserted the new block inside the old block structure (in addition). In this case, you will have two meshes, which can be merged later (for example).

On the other hand, usually, you don't need to merge meshes from several block' topologies if you are using relatively simple geometries. So, you could try to use only one blocking structure, to divide it as you wish and to do some modifications on it (o-blocks, c-blocks, sweep blocks, y-blocks, deleting blocks, etc).

if you would post here a sketch or hand-drawing of your geometry (if you are able/allowed) it would be easier to understand the problem and to share some ideas about the block-structure you need.

DST

camoesas October 6, 2010 08:46

Hey DST,


Yes i have introduced the new block into the old blocking structure. It was of another colour because for no reason it belonged to another part, but i could fix it.

I know a picture says more than 1000 words, but unfortunately I am not able to upload pictures at the moment. Furthermore I dont know if I am allowed to, will check this.

I'm not sure if 'merge meshes' will help me. Im trembling because I have deleted a pipe out of the original geometry.

Simon


Ps: I have searched the forums and the Manuels for an easy way to create a C-Grid but without hits. After some experimental work i found this solution. Ill post it here so maybe it will be usefull for somebody with the same problem:
Its the same proceedings as for O-grid, but you have to select additionally the faces on the open long side of the C.
It is an easy way but it isnt stated clearly nowhere.

PSYMN October 6, 2010 17:48

Why remove ogrids or insert blocks?
 
Simon (other Simon ;) )

I didn't give any instructions about removing Ogrids or inserting a new block... You should have just split your existing blocking and deleted the stuff you didn't need.

Was that not possible...

I guess a sketch or image would be necessary to understand why.

Psymn <= as a unique identifier ;)

camoesas October 7, 2010 02:13

Hey Simon/PSYMN,

I modified the geometry a little bit, because of that I had to insert a new block. Before I have splitted the existing blocking, I removed the O-grid because I was told it can cause Problems to split the O-grid.
After the splitting I inserted a new C-Block.

Simon

Edit: Ive clearified that and I am not allowed to post any pictures. Its a pitty it could save me a lot of words

dst October 7, 2010 03:17

3 Attachment(s)
Hi Simon,

Concerning the new blocks insert, I would suggest you to try to work with only one block structure if possible.
So, if I would modify geometry for some CFD simulation, I would make a new blocking and delete the old one.
It is just easier than having several block-topologies in one mesh.

If you are interested, I could post here one 2D symmetry model with some inner-sharp edges and crazy block-modifications. Maybe you could use some ideas from there. But I should mention, that the problem was just a rough-mesh model for the draft-like heat-transfer problem almost without any flows.

Best regards,
DST

updated:
Attachment 4890

Attachment 4891

Attachment 4892
Heat transfer draft-simulation. O-block, Y-bock, Swept blocks. For the regions where quality was not required, swept blocks have been used.

camoesas October 7, 2010 05:13

Hey DST,

Please post your model here maybe I can addapt some ideas

Simon


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