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Blocking difficulties
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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 |
- 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 ;) |
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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! |
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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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. |
hey there,
as everybody says, those edges are difficult to tackle, i had some free time this morning to try something: https://dl.dropbox.com/u/35161486/cfdsim.png black arrow indicates change that has to be done to get a good quality: https://dl.dropbox.com/u/35161486/cfdsim2.png 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 |
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 |
Here is my first try. Mim angle is 9 deg and I must think another smart topology:. Thinking........;)
http://imageshack.us/a/img833/435/quarterpipe1.png http://imageshack.us/a/img607/5184/quarterpipe2.png http://imageshack.us/a/img197/4949/quarterpipe3.png PS: I am going to work on topologies/geometries to whom I have promised. |
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 |
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 |
Great. Thank you!
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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
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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 |
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. |
Please turn-off the solid and VORFN
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Thanks! Stupid mistake :-D.
I think its time to look at what the solver might say to this mesh then :-). |
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 |
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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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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The simulation aborts after 20 iterations...at the beginning the convergence looks good, but after a while it starts to diverge.
I will look into the problem tomorrow, because i had some other things to do. Hopefully i will find a solution, or the blocking and the guideline of energy382 will solve my problem :-). |
Never mind...problem solved, but i can't delete my post^^.
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How did you solve your problem? was it is error due to mesh or solution parameters? Did you try the energy382's method? I would be interested to see the meshing by this method, as mesh looks promising.
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Hey Far,
the problem that i was refering to was a problem with extending the faces. This one is solved :-). My other mesh did not converge as good as i want it to be, so i decided to try energy382's method. Iam not quite finished and have another appointment today, so i hope that i will be ready by the evening. I will post a picture of the result and if you like the project-file when iam ready. |
I've a customer meeting and will not be at offfice today. I'll make some pics tomorrow. I've to mesh my volute first, but I'll get back to you as soon as possible
You've to choose the outer faces of solid blocking, not the inner ones. (to extrude fixed distance) |
Hello Energy382,
the problem with the extended faces is solved :-). I just had to figure out which combination works well. I do have a meeting soon too, so i will get to my blocking in the afternoon. Sadly i am stuck at the part with the "create blocking from faces". I adjusted some more splits, but i do not get a cut at the top. So i do not have a face at the top of the rip_outlet. I will post a picture later on. |
There has been a change in my geometry, so i will not finish my blocking today...
I will upload my blocking later. Iam still stuck at the part were i connect the c-grid to my rib. http://dl.dropbox.com/u/30926816/Pipe_New.zip The new geometry will have a longer Outlet, and in the middle of the outlet will be a parabolicle body (axially symmetric) which goes down to nearly the ribs (not touching it!). I will prepare the geoemtry today and hopefully will find a way to block it right tomorrow, but iam not sure that this will be so easy. I will try to upload it tomorrow so you can look at it. |
Sorry for the delay, but there are some major problems with my geometry. As soon as they are fixed i will give you guys an update on how the progress with the blocking is.
kind regards John |
Your geomtry isn't complex!!!
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The major problem has nothing to do with the geometry itself :-). Sorry if it sounds like this. |
So it is confirmed that angle less than 20 does not work for CFX?
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My problem has something to to with the additional part, which was missing in the beginning. It hasn't been manufactured yet, nor has it been drawn. So i have to wait some time, till i get the rest of the necessary geometry.
The angle problem hasn't been solved yet, because of the missing part. But i read a lot of literature about the problem with the angle and i think i will wait and look how my solver will solve the mesh. What i can say is, that cfx does solve meshes with a angle quality under 20° (My worst was down to 9°). But i guess it depends a lot on what kind of geometry iam using. I will be happy to give some more informations on this topic, as soon as i have an working mesh and some results :-). |
I've attached blocking (right_side). try the left side on your own!
after blocking, you've to move some vertex and set edge paramters etc. to improve mesh quality right_side_pipe.zip |
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Thanks a lot! I've done the blocking and did the association, but the mesh still looks kind of funny (See attachment). I'm not sure how to make it "smooth", but i think that the problem has something to do with the associations.
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is that your blocking or mine? looks like there are still some missing blocks or there are wrong associations. click "edge" "show association" to check.
upload the current blocking |
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Sorry, but the project is to big to upload it directly on this forum. I can send you later a link via dropbox if you need it.
Here are some more pictures which might give you a clue. I took your blocking and tried to block the other side like you did. It looks all right i think, so i guess it has something to do with the associations. thanks John |
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you could also delete SOLID blocking |
Hmmm...the surfaces were enabled. After i deleted the solid part the meshing did not really improve :(.
http://www.file-upload.net/download-...pe1.1.zip.html I hope you can open it. |
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