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[ICEM] Meshing of a parabolic trough

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Old   June 8, 2012, 02:31
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Here is the final blocking with finishing touches. It took less than a hour to make the blocking and another hour to fine-tune it.


But took hours to rectify some duplicate blocks which were never created intentionally and min quality was ~-0.9 . These were so thin, when blocks were activated they were not visible with naked eye. So when moved some vertices, then I realized double vertices hence duplicate blocks. So moved them and merged them with internal vertices (on inside Oblock in the wing or scoop).

After removing them, now min quality is higher than 0.4. Also during this process (above paragraph), I was trying different processes to improve quality, one of them was to increase the no. of nodes on edges. Therefore mesh size was increased to around 4 million, now you can reduce the size without affecting quality much.

I am attaching both files (with problems of duplicate blocks and final good quality blocking), so this may help others how the problem can popup from nowhere and how to work around in ICEM to deal with them.

Hope you like my little effort (credit goes to the creater of this blocking, Simon)
Attached Files
File Type: zip parabolic_trough_bazinga_Far_duplicateblocks.zip (73.2 KB, 10 views)
File Type: zip parabolic_trough_bazinga_Far.zip (75.3 KB, 17 views)
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Last edited by Far; June 8, 2012 at 04:32. Reason: typo
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Old   June 8, 2012, 12:32
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I forgot to place the horizontal split. But it is important to do so

Pics:






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Old   June 13, 2012, 08:05
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So I tried to create a mesh with your ideas but I have problems to find the reason why the mesh is very bad around the trough.I spent a lot of hours figuring it out and trying a lot of things to get this mesh better but failed.

I hope you can help me out once again.

I attached some pictures (third pictures shows all cells <0.4 quality) and a zip file so that you can see what my problem is.


Thanks again for your great help!
Attached Images
File Type: png premesh.PNG (41.9 KB, 34 views)
File Type: jpg blocking.jpg (23.1 KB, 35 views)
File Type: jpg badcells.jpg (47.1 KB, 38 views)
Attached Files
File Type: zip parabolic_trough_bazinga.zip (57.9 KB, 7 views)
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Old   June 13, 2012, 10:40
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Align edges with curves. For this use edit edge menu.
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Old   June 14, 2012, 05:09
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Align edges with curves. For this use edit edge menu.
Thanks for your answer.

When i go to Blocking -> Edit Edges I have the options Split Edge, Unsplit Edge, Link Edge and Unlink Edge.

I find the align edges with curves option under Geometry->Create Faceted->Align edges to curve.

I tried both the Link Edge tool and the Align edge to curve tool this morning but couldn't eliminate the bad cells.
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Old   June 14, 2012, 05:22
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Do you have thin blocks (as discussed above). I believe it is not the problem with your blocking but you can recheck. Lets say it has 10% priority in our list.

Now the major problem is the edge to curve association. By default edge will follow the nearest curve (This is serious problem when you selected all edges and all curves while making edge-curve association) . In this case you must apply the spline or automatic linear (use this command after setting the edge mesh parameters with enough no of nodes : at-least 50-80) on green edges. Once this is done then go to 3rd button > link edge shape and select the appropriate green edge and then black edge. Repeat this procedure for both sides of wing or trough. Also for the edges on the outer boundary.

If you compare your blocking with mine, you will notice extra split on the air-foil trailing edge. It is necessary for same reasons as discussed above (Fig. 4 & 5).
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Old   June 14, 2012, 07:41
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Quote:
Originally Posted by Far View Post
Do you have thin blocks (as discussed above). I believe it is not the problem with your blocking but you can recheck. Lets say it has 10% priority in our list.

Now the major problem is the edge to curve association. By default edge will follow the nearest curve (This is serious problem when you selected all edges and all curves while making edge-curve association) . In this case you must apply the spline or automatic linear (use this command after setting the edge mesh parameters with enough no of nodes : at-least 50-80) on green edges. Once this is done then go to 3rd button > link edge shape and select the appropriate green edge and then black edge. Repeat this procedure for both sides of wing or trough. Also for the edges on the outer boundary.

If you compare your blocking with mine, you will notice extra split on the air-foil trailing edge. It is necessary for same reasons as discussed above (Fig. 4 & 5).
I already looked for thin blocks yesterday and could not find any. I moved all the vertices around the trough but there were no double vertices. But the bad cells which are shown in my third picture above have no thickness at all. This would be the result of very thin blocks, right? I just might just have not found the thin blocks? Could there be another reason why these cells have not thickness?


I added a picture which shows my associated edges to curves. Its basically the inner part of the O-Grid which is associated to the curves of the trough on both sides.

I'll try your suggestions of linking the edges. After that I'll try your suggested blocking on the trailing edge.
Attached Images
File Type: jpg associations.jpg (29.2 KB, 20 views)
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Old   June 14, 2012, 07:44
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Quote:
I already looked for thin blocks yesterday and could not find any. I moved all the vertices around the trough but there were no double vertices. But the bad cells which are shown in my third picture above have no thickness at all. This would be the result of very thin blocks, right? I just might just have not found the thin blocks? Could there be another reason why these cells have not thickness?

I dont think so it is the case with your blocking.


Quote:
I added a picture which shows my associated edges to curves. Its basically the inner part of the O-Grid which is associated to the curves of the trough on both sides.
Yes, association is correct. But as I described already it will create problem. See this thread ICEM Scripting Issues
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Old   June 15, 2012, 04:06
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Quote:
Originally Posted by Far View Post
Now the major problem is the edge to curve association. By default edge will follow the nearest curve (This is serious problem when you selected all edges and all curves while making edge-curve association) . In this case you must apply the spline or automatic linear (use this command after setting the edge mesh parameters with enough no of nodes : at-least 50-80) on green edges. Once this is done then go to 3rd button > link edge shape and select the appropriate green edge and then black edge. Repeat this procedure for both sides of wing or trough. Also for the edges on the outer boundary.

If you compare your blocking with mine, you will notice extra split on the air-foil trailing edge. It is necessary for same reasons as discussed above (Fig. 4 & 5).
I tried this in different ways and i still have those bad cells.
I splitted the green associated edged with automatic linear after I increased the number of nodes to 80. The edges "jumped" on the curves of the trough.
After that I linked the blue edges around the trough to the green ones and they were shaped like the trough after that. I also tried to cut the edges of the trailing edge before and after this procedure but it didn't solve my problem.

I also forgot to mention that i splitted the blocks in the field one more time to be able to create a nearfield later (see pictures). I hope this doesn't cause these bad cells.

Once again thanks for your help, Far. I appreciate it A LOT!
Attached Images
File Type: jpg nearfield.jpg (25.1 KB, 17 views)
File Type: jpg nearfield2.jpg (31.8 KB, 10 views)
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Old   June 15, 2012, 04:19
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I also noticed that I have an extra split in the middle of the trough. There seem to be to edges which are almost identical but there is a small gap between them. See pictures (from old a blocking version) to compare your splitting to mine.

edit: I merge some blocks there and this problem seems to be fixed now
edit2: Maybe this solved the problem. My Laptop ran out of battery and I have no power supply for it here but with his last breath I created a pre mesh where the worst quality was -0.1. That is the best I had to this point so I hope I will create a good mesh on the weekend.
Attached Images
File Type: png cut in the middle far.PNG (11.2 KB, 8 views)
File Type: png cut in the middle me.PNG (47.8 KB, 9 views)

Last edited by Bazinga; June 15, 2012 at 05:33.
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Old   June 16, 2012, 05:35
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Alright, I still have some bad cells left which have a quality of ~-0.1.

I might found the reason but wasn't be able to fix it. The boundary edges aren't split like the edges directly at the trough. The splits from the O-Grid around the trough do not go through the domain. I tried to split the blocks afterwards but could not find the right tool to do so. To explain my problem I added two pictures. First the boundary edges which are nicely splitted (Fars work) and picture two shows my boundary edges which have not the splits of the O-Grid.

edit: Ok, solved this problem also. Now my worst cell has a quality of ~0.35 without finetuning the mesh. I hope this will work now.

Once again, thanks everybody. I really appreciate your help.
Attached Images
File Type: png splits_at_the_boundary.PNG (33.7 KB, 14 views)
File Type: png no_splits_at_the_boundary.PNG (13.8 KB, 14 views)

Last edited by Bazinga; June 18, 2012 at 10:43.
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Old   June 19, 2012, 08:38
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Quote:
Originally Posted by Bazinga View Post
Alright, I still have some bad cells left which have a quality of ~-0.1.

I might found the reason but wasn't be able to fix it. The boundary edges aren't split like the edges directly at the trough. The splits from the O-Grid around the trough do not go through the domain. I tried to split the blocks afterwards but could not find the right tool to do so. To explain my problem I added two pictures. First the boundary edges which are nicely splitted (Fars work) and picture two shows my boundary edges which have not the splits of the O-Grid.

edit: Ok, solved this problem also. Now my worst cell has a quality of ~0.35 without finetuning the mesh. I hope this will work now.

Once again, thanks everybody. I really appreciate your help.
Great....We have also learned new topology tips from Simon while working on this meshing.
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