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October 19, 2012, 06:38 |
Blocking difficulties
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#1 |
Member
Join Date: Oct 2012
Posts: 46
Rep Power: 13 |
Hello!
I hope that i can find some help here, because i just can't get my blocking right. I have worked for 1 year with icem, but i mostly did unstructerd meshing and some easy structured meshs. I have to mesh a pipe with 2 Ribs (at the Outlet) in it. I cut the geometry, so that i have just a quater of it. I thought that this would make things easier, because i can mirror the blocking when i have blocked and meshed it. I made a hole Block around my pipe and after that i started cutting so that i would get an L-Block (after the mirroring i should get as an result my o-grid). Well, after that i did the necessary associations and well after all that i got a mesh that looks just terrible! The Mesh around my half-rib is all right, but the mesh around the other surfaces (Top, Down an the quater boundary surface) are just not fitting right. Am i right that i just have to get a mesh around those surfaces? Because when i mirror it there will be a closed volume in the end. (At least so i hope^^) I hope that someone of you can look at my blocking and give me some hints. Best regards John Last edited by CFD_SIM; October 19, 2012 at 07:14. |
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October 19, 2012, 11:23 |
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#2 |
Senior Member
AB
Join Date: Sep 2009
Location: France
Posts: 323
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- your geometry is not closed, so the premesh won't work propelly because the volume is "open".
- you have to associate all the edges at the top and the bottom of your geometry to improve the mesh. You could rotate the blocking also, but I really don't like this way because it messes up the association (with ICEM 12.1). So here is another method : you should first closed your geometry with interfaces, do the association, generate your premesh, and convert the premesh into unstructured mesh. Then you can rotate your mesh, merge nodes at the interface and delete those interfaces to have your full volume mesh. EDIT : I took a lot at your blocking, and if you want to keep the geometry of the RIB, you should redo your blocking because of the angles of the geometry. If you could simplify your geometry by changing the circular shpa eof the RIB to a rectangular shape, it would help a lot Last edited by BrolY; October 19, 2012 at 11:39. |
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October 19, 2012, 12:41 |
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#3 | |
Senior Member
Christoph
Join Date: May 2011
Location: Germany
Posts: 182
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Quote:
yeah, shape of rib is really tough. you need several o-grids to capture the geometry. be careful....your model has no rotational periodicity, only symmetry. so you've to mesh half pipe instead of quarter pipe and create a surface (symmetry plane). then use a c-grid, do at least two splits in front and behind rib, insert o-grid (around rib) and do another o-grid to capture the edge fillet. as alexander said, things would be much easier without that edge fillet! |
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October 19, 2012, 12:45 |
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#4 |
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Join Date: Oct 2012
Posts: 46
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Hi BroIY,
thanks for your answer. I tried to block the hole pipe, but the result was not better! I have seen a lot of meshs that were made like i tried to do, and they did not have a closed volume. Maybe this is with ICEM 14.0 something different (don't know, because i only worked with 13 and 14) I can post my blocking with the hole geometry on monday...but it actually looked much worse than this. Maybe because iam not that good with the hole blocking. When I try to build a smaller block on the bottom and then translate it up to the top the result is a similar mesh like uploaded. If i make a hole 3D block and split it afterwards the result is not good either. And iam very sorry, but there is no possibility to change my geometrie. I have to mesh it like this (nothing that i like, but something that i have to live with :-) ) |
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October 19, 2012, 13:01 |
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#5 | |
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Quote:
I will talk with my adviser about the edge fillet but i don't think that there are gonna be changes. When it do not have any result by end of next week i think i will switch to unstructered mesh and hope that my quality will be all right. |
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October 19, 2012, 14:53 |
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#6 |
Super Moderator
Ghazlani M. Ali
Join Date: May 2011
Location: Tokyo, Japan
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hey there,
as everybody says, those edges are difficult to tackle, i had some free time this morning to try something: black arrow indicates change that has to be done to get a good quality: i have attached the blocking file, so you can have an idea, i didn't take a look at your blocking, may be that what you did at first sight, sorry if that's the case... When i have a large geometry like yours, so i can focus on the rib only i erase everything else, nothing that the rest is easy and extrude can expand my blocking. it's not always the case https://dl.dropbox.com/u/35161486/Quaterpipe.zip |
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October 19, 2012, 15:24 |
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#7 |
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Join Date: Oct 2012
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Thank you very much Diamondx!
Iam not sure, but i tried to get a blocking like yours. Unfortunately i had al lot of problems with the mesh . I looked at your blocking and it seems pretty good...sad that i could not get to that point. I hope that i can transform it down to the bottom, but this should not be that big of a problem. Thanks again and i hope that thats it with this part :-). greetings John |
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October 19, 2012, 15:39 |
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#8 |
Super Moderator
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Here is my first try. Mim angle is 9 deg and I must think another smart topology:. Thinking........
PS: I am going to work on topologies/geometries to whom I have promised. |
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October 21, 2012, 04:20 |
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#9 |
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Join Date: Oct 2012
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Hey Far!
Your Blocking looks great too. Would you mind uploading your Blocking so that i can have a better look at it. Thanks John |
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October 21, 2012, 04:31 |
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#10 |
Super Moderator
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I tried to attach blocking in previous post, but didn't finish because the file size 133 K exceeds the limit of 97K. Now files are shared through dropbox.
https://dl.dropbox.com/u/68746918/Qu...initialtry.zip |
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October 21, 2012, 06:10 |
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#11 |
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Great. Thank you!
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October 21, 2012, 06:50 |
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#12 | |
Super Moderator
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This post may be helpful to you. Simon is mentioning the that min angle 9 may be OK for Fluent. But you should confirm it. http://www.cfd-online.com/Forums/ans...tml#post262543
Quote:
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October 21, 2012, 07:49 |
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#13 |
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Thanks for the information and the link. I will look into it as soon as i can.
I think at this place the best thing to do is to look what the solver might say :-). Iam not that familiar with the solver in Fluent, is he more prone to a "bad mesh" (min angle less then 9°) or is the solver in ANSYS CFX more problematic? For my simulation i will use ANSYS CFX so it would be good to know. greetings john |
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October 22, 2012, 05:03 |
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#14 |
Member
Join Date: Oct 2012
Posts: 46
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Hey Far,
i have another question for you :-). I took a closer look at your mesh and iam not getting the same result as seen on the pictures that you ugploaded. Is it still the same blocking? Because while i tried to recreate your blocking my quality wasn't that good. So i looked again in your file and there is, for example, the angle much worse. Maybe iam just forgetting something. |
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October 22, 2012, 05:33 |
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#16 |
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Thanks! Stupid mistake :-D.
I think its time to look at what the solver might say to this mesh then :-). |
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October 22, 2012, 14:26 |
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#17 |
Senior Member
Christoph
Join Date: May 2011
Location: Germany
Posts: 182
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I've attached blocking of the rib (note, that it's just a draft. you could of course do some additional splits and/or associations). Just to show you, how to get reasonable cell angles.
next steps to be done: - extend solid blocking (use extend faces with a fixed distance....let's say with a value of 3 or 4 to create o-grid around your rib), create new part (FLUID) and assign these new blocks to fluid part. - uncheck all geometry except pipe_inlet, do another 3-D blocking ("merge" to existing blocking), create C-grid - create two vertical splits (one left and one right side of rib) - extend all blocks except the 3 inner to your outlet - use "create blocking from faces" to connect the c-grid to blocking round your rib (it's possible, that you've to do 2-3 additional splits) - associate edges to curves It's not that difficult. Try it on your own. As I'm busy with my own project, I couldn't do this too. If you've any queries, I'll help you out. download link: Quaterpipe.zip |
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October 22, 2012, 14:38 |
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#18 |
Member
Join Date: Oct 2012
Posts: 46
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I have done the blocking today, as Far showed me. Not exactly like he did, but pretty close. I think with all the practice iam starting to get better :-).
I will try your way tomorrow and will check if my quality does improve, because the solver did not like my mesh much :-D. Thank you for so much advise! I will need it, because the next thing to mesh is a nice little Blade^^. If there are any further problems i will report them, but i hope it will work properly. |
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October 22, 2012, 14:45 |
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#19 | |
Super Moderator
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Quote:
Your method is awesome and new. But I need some practic to do like this, but hope to get help from you in other projects as well as you are way better than me. |
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October 22, 2012, 14:52 |
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#20 | |
Super Moderator
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Quote:
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