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#23 |
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Francisco
Join Date: Mar 2012
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Well, returning to the initial topic of this thread, some days ago I got negative volumes due to bad quality elements, I though it was just on the blade tip but it resulted to be all over the blade surface.
I've done all the blocking again to make it simpler, I've moved vertices to avoid complicated shapes, etc. but I still get many negative volumes (pictures 1 and 2). I've tried the block check options: run-check/fix and fix inverted blocks and nothing changed. ![]() I've converted the mesh into unstructured, checked the mesh and a message says: I choose to fix them"1078 problems were found for volume orientations" "208 elements could not be fixed" "208 elements could not be fixed -- probably the element quality is too bad." ![]() ![]() Then another message appears about non-manifold edges (picture 4) and I choose to fix (441 out of 2644 could not be fixed). ![]() And that's it. How can I improve those 208 elements quality to avoid the volume orientation issue? as I guess volume orientation is the cause of negative volumes. What should I try next? Any ideas? |
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#24 |
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AB
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That looks like to be an association issue. But you should share your .tin and .blk file so we could have a look.
For your record, multiple edge is a possible problem. But if you have 3 or more surfaces which intersect at the same curve, this curve would be considered as a multiple edge. So that's not a problem. But if you have 2 surfaces which intersect at the same curve, this curve should NOT be considered as a multiple edge, otherwise, there is a problem. Non manifold vertices often means nodes which are not connected to other nodes .. |
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#25 | |||
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Francisco
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Quote:
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Merci bien pour l'aide! |
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#26 |
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AB
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On the tree menu, right click on curve -> color by count :
Yellow means that the curve is in contact with one surface. Red means that the curve is in contact with 2 surfaces. Blue means that the curve is in contact with 3 or more surfaces. That colors means something if you have done a build topology. Otherwise, all your curves would be colored by yellow. Are you sure you have associated all your edge with the right curve ? Zoom more around the blade, make picture with the mesh. Do the same without, only with curve and with the option "show association" activated. |
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#27 |
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Francisco
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Here you are some pics:
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#28 |
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It's really hard to help you without the project files ..
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#29 |
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Francisco
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I know, I'm sorry. I'm gonna ask if I can upload the files but that won't be until tomorrow. I'll keep posting.
Thanks a lot. |
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#31 |
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Francisco
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#32 | |||
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Francisco
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I'm very sorry I cannot upload geometry and blocking files. Thanks a lot for your effort guys! |
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#33 |
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#34 | |
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Francisco
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On the tree menu, on topologies, right click and save, it is saved as a blocking file. Then in the other project I had to import that file. I asked for info about that in this thread: http://www.cfd-online.com/Forums/ans...tml#post408760 |
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#36 |
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Francisco
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I'm not sure about that, I just wanted to find a way to import some blocks into a file with many blocks. I think I have to apply the merge option to get just one blocking.
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#37 |
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Francisco
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I've been cleaning the geometry, deleting all redundant curves and points, and making some reading from icem help manual, and I've realized that I have many unattached curves even if it's supposed to be a two surfaces intersection, is that a problem?
The same happens with single and double edges. There are just two multiple edges (blue). I attach some pictures of unattached (green, picture 1), single (yellow, picture 2) and double curves (red, picture 3), a general view of surfaces (picture 3) and a picture with surfaces in grey scale where you can see the double and multiple curves (picture 5). The domain is a 120º cylinder sector with inlet, outlet, two symmetry curved faces and two flat periodic faces. Then there's a prism around the blade with several surfaces. Please, ask me any required info. Thank you very much! |
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#38 |
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#39 |
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Francisco
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Well, I've found that same problem in a way more simple case. It's a 3D flat plate inside a prismatic domain. Even if blocking is very simple, after specifying the bunching in all edges (I don't use to specify surface mesh parameters, are they really necessary?) and pre-meshing, many tiny negative volumes appear (see picture), of the order of 7e-13 and smaller (see histogram in the picture)
I guess this issue has something to do with the blade one, so I'd really appreciate any help, as I'm running out of time... ![]() As it is hard to be helped without .prj .tin nor .blk files I upload them so it's easier to be helped. Thanks you all, guys! |
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#40 | |
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Francisco
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So my questions are: How can bunching generate negative volumes? If an edge has too much nodes it seems to end up in negative volumes. Isn't it a limitation of the size of the mesh? Thanks |
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Tags |
blade tip, hexa mesh, sharp edge, wind turbine |
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