# [ICEM] Blocking and Symmetry

 Register Blogs Members List Search Today's Posts Mark Forums Read

 June 22, 2010, 12:07 #2 Senior Member     Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,662 Blog Entries: 1 Rep Power: 35 Thanks for posting this so others could benefit. Simon

 June 22, 2010, 22:27 #3 Member   Join Date: Dec 2009 Location: China Posts: 79 Rep Power: 7 what is "boco"? Maybe this question is simple, but I'm a beginner of ICEM CFD. thanks

 June 23, 2010, 10:59 BOundary COndition #4 Senior Member     Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,662 Blog Entries: 1 Rep Power: 35 BOCO is short for "boundary condition" Instead of actually mirroring the blocking, if the boundary conditions are symmetric, you could just apply a symmetry boundary condition and get the same solution with half the mesh. However, if the model is symmetrical, but the boundary conditions are not, then you must at least mirror the mesh before you apply your boundary conditions. It is only worth mirroring the Hexa blocking if your model is only mostly symmetrical. You could mirror the blocking to save time on the second half, but then continue to fit the second half of the blocking to the geometry, perhaps adding more splits, drilling holes, extruding faces, etc. to make any "non-symmetrical" adjustments. The flexibility of blocking makes it perfect for this.

 June 24, 2010, 07:25 #5 Senior Member   AB Join Date: Sep 2009 Location: France Posts: 323 Rep Power: 12 Hi all, First of all, our BOCO are not symmetrical, only our geometry is. So we created the blocking for the first half of the geoemtry and we rotate our blocking on the second half. But the issue is that the blocking isn't fitting well the second half of the geometry. There are too many edges and curves to associate themselves manually. Is there another solution? For the interface, we merged the nodes but it created pyramids along the interfaces. How can we avoid that? Thanks, AB

 June 24, 2010, 08:57 Mirror in more detail... #6 Senior Member     Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,662 Blog Entries: 1 Rep Power: 35 Pyramids? I thought this was a hexa model. You should only get pyramids as a way to connect hexas (or prism sides) with tetras (or prism tops). If your geometry is symmetrical, I would just mirror the mesh. If you have some differences in the part naming, there is an option under "Edit Mesh (tab) => Repair mesh" to associate the mesh with the underlying geometry. After you mirror, the nodes should be lined up (hexa elements on both sides). Just do a simple "Edit Mesh => Merge Nodes => With a tolerance" and set a very small tolerance (much smaller than the mesh size). Make sure to turn on the ignore projections option. This will merge nodes on both sides of the mirror so that the hexas are all connected. Next, you will get rid of your symmetry quads. I would do this with "Edit Mesh => Delete elements" then use the selection tool bar to select items in a part (hot key P), and pick that symmetry part. That should be all you need to do. If that doesn't work for you, then I am missing some key bit of info. If you can send me your model and I will figure it out for you. It is probably something simple. Simon

 June 24, 2010, 09:11 #7 Senior Member   AB Join Date: Sep 2009 Location: France Posts: 323 Rep Power: 12 I think I didn't explain our problem very well: When we mirrored the blocking, the association didn't work well when we displayed the mesh with "the pre mesh" option. One way to prevent this issue would be to associate the new blocks with the geometry manually, but we would like to avoid it because they are too many curves and edges in our model. Do you know how to do that? Thanks ! P.S: we had pyramids on one of our test when the premesh was converted in unstructured mesh. But this is not a matter anymore

 June 28, 2010, 05:24 #8 Senior Member   AB Join Date: Sep 2009 Location: France Posts: 323 Rep Power: 12 Our geometry was fully symmetrical, so we only wanted to create the blocking for half of the geometry, and then rotate the blocking. But it didn't work because the association was very bad: the rotated blocking was still associated with the first half part of the geometry. But, hopefully, we found a way to fix this issue: 1) we rotate the blocking 2) update association (only vertices and edges, NOT faces) 3) meshing parameters with "keep counts" options And the pre-mesh worked well.

July 31, 2012, 06:29
#9
Senior Member

Join Date: Mar 2009
Posts: 138
Rep Power: 8
Quote:
 Originally Posted by PSYMN Pyramids? I thought this was a hexa model. You should only get pyramids as a way to connect hexas (or prism sides) with tetras (or prism tops). If your geometry is symmetrical, I would just mirror the mesh. If you have some differences in the part naming, there is an option under "Edit Mesh (tab) => Repair mesh" to associate the mesh with the underlying geometry. After you mirror, the nodes should be lined up (hexa elements on both sides). Just do a simple "Edit Mesh => Merge Nodes => With a tolerance" and set a very small tolerance (much smaller than the mesh size). Make sure to turn on the ignore projections option. This will merge nodes on both sides of the mirror so that the hexas are all connected. Next, you will get rid of your symmetry quads. I would do this with "Edit Mesh => Delete elements" then use the selection tool bar to select items in a part (hot key P), and pick that symmetry part. That should be all you need to do. If that doesn't work for you, then I am missing some key bit of info. If you can send me your model and I will figure it out for you. It is probably something simple. Simon
HI Simon, Hi Everybody,

I am still having problems mirroring my mesh the way you described it here.

1. I am mirroring the mesh (Merge Nodes: automatic; Delete duplicate elements)
2. Merge Nodes: Like you have described it: (ignore projection, tolerance 0.01)
3. Delete Symmetry Plane

But Check Mesh still gives me:
- uncovered Faces
- multiple Edges
- non manifold vertices

I ve tried a lot like varying the tolerance, mirroring with and without symmetry Plane but it still doesnt work. Maybe somebody see the mistake??

Thanks
__________________
OF - 2.0.0

 July 31, 2012, 07:12 #10 Senior Member   AB Join Date: Sep 2009 Location: France Posts: 323 Rep Power: 12 Non manifold vertices are usually due to association problems. Be sure you have associated all the edges at the interface where you merge the nodes. Multiple edges is only a possible problem. If you have a T junction for example, it's normal to have multiple edges. Uncovered faces means some shells doesn't belong to any parts. Some Fix the trouble and adds the shells to the right part. P.S : post some pictures, it might help

July 31, 2012, 08:14
#11
Senior Member

Join Date: Mar 2009
Posts: 138
Rep Power: 8
HI Broly,

Here is my case. As you can see its an simple cube on sticks. I dont know what screenshots could be of any help. So if you need additional information please let me know.
If I choose add uncovered edges to Fluid I get a Wall in my Fluid. The Symmetry plane is back just with a different name....

Now I am getting additional error messages when checking the mesh:

- probleme volume elements
- duplicate elements
- volume orientation

I am on the right way but in the wrong direction...

edit: blue is the symmetry plane, pink is the cube.
Attached Images
 cube.jpg (48.5 KB, 91 views)
__________________
OF - 2.0.0

 July 31, 2012, 08:44 #12 Senior Member   AB Join Date: Sep 2009 Location: France Posts: 323 Rep Power: 12 Don't add the elements to the fluid ! If the uncovered elements are attached to the symmetry plan, then add the elements to the symmetry plane part. if duplicate elements appears, delete them.

 July 31, 2012, 08:57 #13 Senior Member   Join Date: Mar 2009 Posts: 138 Rep Power: 8 HI Broly, but id like to delete the symmetryPlane part. Somehow I have to add the former symmetryplane elements to the inner fluid. If i add them to the (now empty) symmetryplane part I simply revive it.? __________________ OF - 2.0.0

 July 31, 2012, 11:10 #14 Senior Member   AB Join Date: Sep 2009 Location: France Posts: 323 Rep Power: 12 Post an image with the location of the uncovered faces.

July 31, 2012, 12:02
#15
Senior Member

Join Date: Mar 2009
Posts: 138
Rep Power: 8
HI BrolY,

Here is a snapshot of my unconected vertices. They are exactly were there was the symmetry plane.
Attached Images
 cube1.jpg (70.0 KB, 60 views)
__________________
OF - 2.0.0

 August 1, 2012, 03:55 #16 Senior Member   AB Join Date: Sep 2009 Location: France Posts: 323 Rep Power: 12 Unconnected vertices is not an issue. Post the same picture with the uncovered faces.

 August 1, 2012, 04:30 #17 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,914 Blog Entries: 6 Rep Power: 38 if possible post .tin and .blk

August 2, 2012, 08:01
#18
Senior Member

Join Date: Mar 2009
Posts: 138
Rep Power: 8
Quote:
 Originally Posted by BrolY Unconnected vertices is not an issue. Post the same picture with the uncovered faces.
Sorry I mixed it up. At the moment I am not in office I will do so next week.

Thanks
__________________
OF - 2.0.0

August 8, 2012, 07:53
#19
Senior Member

Join Date: Mar 2009
Posts: 138
Rep Power: 8
HI Broly,

Here are my tin and blk files:
Attached Files
 files.zip (60.0 KB, 16 views)
__________________
OF - 2.0.0

 August 8, 2012, 12:37 #20 Super Moderator     Sijal Ahmed Memon (turboenginner@gmail.com) Join Date: Mar 2009 Location: Islamabad Pakistan Posts: 3,914 Blog Entries: 6 Rep Power: 38 Steps are : 1. Mirror geometry 2. Mirror blocking 3. Update association 4. Edge to surface association Make sure surfaces are also copied and rename them as deemed necessary. Both files are attached: 1. Before mirror 2. After mirror (Blocking is bit different) Shot at 2012-08-08 Shot at 2012-08-08 Shot at 2012-08-08 Shot at 2012-08-08 Shot at 2012-08-08 Shot at 2012-08-08 Shot at 2012-08-08 Shot at 2012-08-08 Shot at 2012-08-08 Shot at 2012-08-08 sharonyue likes this.

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post ShaneStan ANSYS Meshing & Geometry 49 December 4, 2011 14:48 Anorky ANSYS Meshing & Geometry 12 August 17, 2011 21:28 Joe CFX 9 August 31, 2006 08:01

All times are GMT -4. The time now is 22:55.