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Old   April 20, 2011, 11:45
Default 2D Ogrid
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Hi

I'm trying to create an O-grid in a 2-D geometry. I've completed the 2-D car tutorial. However, I'm still unable to create the required mesh. I've attached a picture of the geometry and a primitive mesh. Essentially what I want to do is create a grid such that I have concentric semi-circles from the semi-circular notch in the geometry.

I suspect it's something to do with selecting the blocks, but I've tried everything I can think of.

Thanks.
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Old   May 3, 2011, 13:49
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HY!

mesh u want should have a semi circle concentric far-field, otherwise you have to split around the circular area (two vertical and one horizontal splits)
then split middle block as O-Grid and select the lower horizontal edge to create what is called C-grid.
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Old   May 6, 2011, 07:36
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select "around block(s)" when you create O-grid
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Old   May 16, 2011, 13:00
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Quote:
Originally Posted by JOKER View Post
HY!

mesh u want should have a semi circle concentric far-field, otherwise you have to split around the circular area (two vertical and one horizontal splits)
then split middle block as O-Grid and select the lower horizontal edge to create what is called C-grid.
Many thanks for the reply. I've tried this but the mesh still looks strange. This is what I've done.

I first create a 2-D planar block around the geometry. Then I create a horizontal and vertical splits around the semi-circular area. I then delete the block that is not needed (i.e. the square block formed from the splits, since the semi-circular region is empty).

Then I do the O-grid by clicking the middle block (the deleted block is in part VOFRN which I do not select). I also select the lower horizontal edge between the two vertical splits. I also select the option "Around block". I've attached a picture of how the grid looks now.
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Old   May 17, 2011, 02:01
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Are you looking for something as shown in either of the attached images (or) Can you show more images of the geometry
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File Type: jpg img2.JPG (66.7 KB, 63 views)
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Last edited by saisanthoshm88; May 17, 2011 at 04:20.
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Old   May 17, 2011, 07:04
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Quote:
Originally Posted by saisanthoshm88 View Post
Are you looking for something as shown in either of the attached images (or) Can you show more images of the geometry
Hi, the geometry is essentially the same as what you've just shown, however the semi-circular cut is very small compared to the domain. After a few tries I was able to get the following mesh, but my CFD results do not look right.

I believe that the first mesh you posted (the one on the left) is a better mesh than the one I have.
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Old   May 17, 2011, 08:49
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Quote:
Originally Posted by lost.identity View Post
I believe that the first mesh you posted (the one on the left) is a better mesh than the one I have.
Hi,

I feel that this is only a problem with the positioning of the vertices in the blocking. If not try the topology exactly as shown in my first image it shouldn't really matter even if the semi circular cut seems smaller. Post a image that shows the edges of your blocking.

And then regarding the results even I had a similar experience earlier while simulating flow past a 2D cylinder ( in CFX ). I believe that results in these sort of problems vary much with the boundary layer resolution but im not sure of this.

So please let me know if you get to figure out the reason behind the erroneous results
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Old   May 18, 2011, 00:23
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Well ok I see that you have done a blocking as shown in the image attached here. but yes my first image in the last post gives you a better mesh it's all just about some additional splits I made there before generating the O- grid
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Old   May 18, 2011, 12:06
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You have a half circle in a box... So you started correctly.

One horizontal split for the top of the circle, two vertical splits to capture the left and right side. Then associate the appropriate edges with the circle, walls, etc.

Then two paths.

1) Don't delete the block in the circle... Go to the PARTS branch of the tree and create a new part called Solid. Add the circle blocking material to that part. This is just for easy selection later. For Ogrid, select that Solid Block. Also select the Edge against the wall. Make sure to select the "around blocks" option. Apply. You will get what sai showed in his first picture.

2) Lets assume you did delete that circle block... You can still proceed, but there are more items to select. Go into OGrid and Select all the blocks in the model. Then select all the edges in the model EXCEPT the ones along the half circle. Make sure "around blocks" option is OFF. Apply and you will get what sai showed in his first picture.

You could start over and do it this way...

3) You could split just a little up from the circle and a little ahead and behind the circle (Split for the outside of your boundary layer). The advantage here is that your far field won't need alignment later. Don't associate anything yet. Instead, go into Ogrid and select just the block with the circle in it. Then select just the edge along the bottom... Make sure "around blocks" option is OFF. Apply. Then delete the Hgrid block at the center of the CGRID you just created. Then associate all the edges with appropriate curves...

4) Many other ways to get to this blocking... you could do it all with Hgrid, etc.
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Old   May 31, 2011, 20:13
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Going off of what psymn and sai described, here are some pictures:

1: One horizontal split with two vertical splits as shown.

2: Associate edges around the semi-circle to the the semi-circle curve.

3: O-grid split the semi-circle block and the bottom edge as shown. Make sure to select 'around blocks' check box when making O-grid. Also, add the semi-circle block to a new part.

4: Shown is the initial pre-mesh after O-grid split.

5: Move vertices to to straighten out the topology as shown.

6: Adjust line parameters to add more nodes along a line. Make sure to select 'copy parameters' check box.

7: Final grid. Further adjust as necessary. Turn off the semi-circle block in the parts tree display too.
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File Type: jpg 2.jpg (32.3 KB, 62 views)
File Type: jpg 3.jpg (34.4 KB, 64 views)
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Last edited by dim_slo; May 31, 2011 at 22:48.
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Old   May 31, 2011, 20:27
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last two pics...
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