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-   -   [ICEM] Problems with O-grid (http://www.cfd-online.com/Forums/ansys-meshing/96203-problems-o-grid.html)

Lilly January 16, 2012 10:03

Problems with O-grid
 
Dear all,
I have two questions concerning the O-grid generation which are quite stupid questions, but I wasn’t able to find the answer at the "Help Topics" or anywhere else:
  • I generated my blocks using the “Extrude Faces” option. If I want to create the O-grid afterwards I can only pick the Faces at the inlet an outlets of my geometry at “Select Faces” and not the faces in between two blocks. Does anybody know how I could achieve this?
  • I created an O-grid before I moved the vertices of the original grid in the proper location (I know that was stupid) and tried to correct both the vertices of the blocks and the O-grid afterwards, but now the O-grid edges look totally messy. Is there any possibility to delete the whole O-grid and create a new one fitting to the corrected blocks afterwards? I tried to remove the O-grid in different ways, for example by merging the blocks, but nothing worked…
It would be really nice, if somebody could help me!
Thanks a million in advance,

Lilly

kiran January 17, 2012 13:01

hi
 
Hi

answer to your first question you cant see the intermediate faces when your trying to select.
The logic is when you select inlet and outlet faces the intermediate faces also get selected automatically. I mean it makes through operation.

Still if u want to select the intermediate faces just go near to the face and select it. Its get selected even though u cant see that face. But u can see after selecting. it appears in blue.

Answer to your second question

just go the merge vertices option and turn on propagate merge option. then merge using two vertices. The entire o grid will be merged.

PSYMN January 17, 2012 18:35

Selecting a face simply allows the ogrid to pass into the next block. You can't see it, but when you selected the face on the INLET, it really also selected the adjacent VORFN block and allowed the OGRID to pass into that dormant block.

There is no need to select a face between two blocks that you can see. Just select the adjacent block and you have the same affect.

You can not terminate an Ogrid in a volume, it must be able to "turn around" or you would leave hanging nodes.

For your second issue, Kiran is right. Merge Verts with "Propagate" will collapse the Ogrid index away so you can recreate it. You could also use "Reset Ogrid Orthogonality" under "Blocking (tab) => Edit Blocks".

Lilly January 18, 2012 06:59

O-Grid Offset
 
2 Attachment(s)
Thanks to both of you!
Your advices are working fine!
But I got another Problem concerning the O-grid now:
Is there any way to scale the O-gird in relation to the size of the single blocks (or edge lengths)?
I am asking since my geometry is pretty complex: there are narrowings and the diameter of the inlet is much larger than the diameter of the outlets. Therefore my O-grid looks either at the inlet or at one outlet acceptable depending on the "Offset" (see pics). I tried both changing the "Offset" at the creation and at the rescaling of the O-grid.
Thanks a lot for your ideas and help in advance!
Lilly

PSYMN May 22, 2012 10:04

Sorry I am so behind in my emails... But I thought I would answer this one anyway...

Yes, you can use "rescale Ogrid". Adjust your index control to only see the half of the model that needs adjusting and then rescale the Ogrid. It will leave the other part alone and the ogrid height will change linearly between.

You can also manually adjust edge length to tweak things more precisely.

user_of_cfx May 24, 2012 09:35

Hello,

I have an O-grid problem too. Even though I want to split the blocks inward, in some parts of my geometry the O-grid is created around the blocks, messing everything else up. I have had this before, and I just had to re-adjust the vertices because apparently some angle was not quite right, but I tried that now and it's not working.

The geometry is roughly a bent tube, a type that I have meshed several times before using the same method of placing several blocks to follow the curvature.

If I learn what may be causing this problem I should be able to work out a solution.

Many thanks,
Christa

diamondx May 24, 2012 09:43

The way i generate O-GRID: split block -> OGRID , then you can select if you want your ogrid around your block or not and define an offset for it.
If your ogrid happens to not be the result you wanted you can modify it in edit block -> modify ogrid.

user_of_cfx May 24, 2012 09:48

Thanks, Ali.

I don't want my O-grid around the blocks and I specify that I want it so. Out of the around 50 blocks that I am using, I get the unwanted O-grid around the block for about 3 of them. I tried moving the O-grid vertices inwards, but the resulting mesh is horrible anyway. It' some kind of bad setup or glitch, and changing the original settings (namely the offset), does not alter the direction of the O-grid, just the size of it.


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