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[ICEM] 3Dcar- multi-block hexa mesh

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Old   August 31, 2016, 14:29
Default 3Dcar- multi-block hexa mesh
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Hi everyone,
Beginner here, having a panic attack.

I have been asked to make a hexa mesh for a 3D car model (audiA8) using ICEM only.

geometry clean up:
I deleted half the car since its symmetric, created a wind tunnel box, replaced wheels with cylinders, simplified some features, re-organised the surfaces into parts, deleted ALL points and curves, created a new set by using the build diagnostic topology option.

The build topology tool felt too good to be true, is there some down side to deleting all the default curves(which were far too many to make sense of)/ using the build topology tool?

Several of the surfaces seem defective to me. if i zoom in enough, i can see holes in many of the surfaces, especially at the interface of two different surfaces, it looks like a real mess. The "close hole" tool requires a closed curve around the hole.. but there aren't any curves...and there are far too many such holes. Some surfaces taper into a sharp edge, some overlap. I think this will give me hell when i do the blocking process.

the procedure and tools I know how to use are:create block, split blocks, create O-grid block, make associations, move vertices...

I made a brief attempt at carrying out those steps, and it felt like an impossible nightmare.

I am under the impression that tetra meshing is the norm for geometries such as this... is it so?

so, I want to know, is this even possible? Or Is the chance of successfully creating a multiblock-hexa mesh so slim that its not worthwhile?
Should I be looking for some other method?

If this is possible, are there any additional tools/hacks that i should explore?
any suggestions on how to approach the problem? (i was thinking of an O grid around the mirror), any suggestions to further clean up or simplify the geometry? what should I do about the gaps and holes in the surfaces?

Thank you
P.S sorry for the bad picture, not my system, so i am not at liberty to take screen shots.
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Old   September 8, 2016, 09:31
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These kind of geometries can be meshes Multiblock meshes by simplifying the geometry. You may have to look into options like CADfix to merge or combine surfaces to Mesh in ICEM. The other Multi-block meshers where you can explore are are GridPro and Numeca. Moceon can also be a choice.
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Old   September 9, 2016, 20:09
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Hello jumpmonkey

it is possible to create a structured mesh for this geometry. However this can easily be a whole week of work, for a beginner maybe even a month... You will save some complexity by creating a smooth car body "like" an Ahmed body.
I guess though this is not an option for you. The wheels and front panel inlets add a lot of complexity to the blocking. It will take good planing how to create the blocking to not end up with moving "millions" of vertices.



When using topology built you can switch of the deletion of curves. This would be a good idea in case you need these curves for association.
For structured blocking it is not neccessary to have a watertight geometry. Though it helps.

Unstructured meshes are somewhat standard for complex geometries. It takes an intermidiate level of meshing to produce a runable mesh. Too often, this is all that is needed. But remember, for unstructured meshing you need a watertight geometry...

In general i prefer structured over unstructured meshes. Though in your case i would apply some hybrid meshing, or if possible chimera grids; with other words using unstructured blocks only for the most difficult parts. Or, just "simply" unstructured.

Some more general suggestions regarding blocking:
Save often and make many backups of blocking and geometry
Split only what needs to be splitted
Edge params setting is one of the last steps
Consider using a 3d mouse like the 3dconnexion devices, it will prevent stress on your hand of too often scrolling =) using icem is much more convinient this way.

With regards,
Sebastian
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Old   September 10, 2016, 11:25
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My last experience with ICEM's blocking dates back to 2013 when I tried to adopt it as a mesh tool for my day-to-day working activity. That time ICEM seemed to be a joke in this regard. Wanna build nice all-hexa mesh for your real-life (industry-level) 3-D geometry with blocking? Don't even think about it! At least it was so 3 years ago. It might have been improved since then, have it?
My questions regarding ICEM were asked here: http://www.cfd-online.com/Forums/ans...ssues-day.html
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Old   September 15, 2016, 22:24
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Thank you all for replying

Took me two weeks, but I finally got it done! ... I think i've made too many simplifications to take the result seriously, but i've gotten pretty comfortable with multiblock-hexa. I'll try and learn unstructured now
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Old   September 16, 2016, 12:22
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Can you show (off) some pictures with your nice blocking and mesh? It would be interested to see if ICEM has really advanced in the right direction through all these years. Thanks.
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Old   September 18, 2016, 11:21
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:P it's nothing to look at... as I said, I've made some very dramatic simplifications.
I cannot answer on whether the software has changed over the years, because I have used only the basic tools, and haven't tried the bottom-up approach. But I don't see any difference between ICEM 15.0 and the description in your post.
I never had to touch the 'edit block' option...
Keeping with bluebase's advice, I tried to keep the number of splits as well as associations to a minimum.

I totally understand your frustration, it was very tedious, and I am not even sure that I can do it again...
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