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Model assemble - meshing strategy

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Old   July 13, 2014, 18:46
Default Model assemble - meshing strategy
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Lefteris
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Hello again. So here is a description of the situation.

My geometry comprises of :
1. fuselage, 2. wing, 3. winglets (whitcomb), 4. pylon, 5. nacelle and 6.turbine.

I assembled them in 1 model. To be more precise, first I put the fuselage bits together. Then the wing and I added it to the fuselage. Afterwards the pylon. Then the nacelle and the engine and I assembled them with the pylon and then I added this selection to the fuselage-wing model. Finally, I assembled the model of each winglet and added those to the rest as well. Each time I used different tolerances in order to get the model assembled.

However, when I try to split the to remove the turbine let's say, the winglets are removed from the model too and then I cannot add them again. The same happens if I try to add a model. For instance, I realised that when I was putting the pylon together, I forgot a surface that sits on the engine so I created the coons patch and its model but when I added it to the greater model, the winglets came off again (and I couldn't understand if this surface was indeed added to the model)

What am I doing wrong?


I have attached 2 pictures to help you understand how the geometry is. The part that I want to add is the part of the pylon that sits on the turbine (figure 1).
Please notice that the turbine does not end where the nacelle ends and the engine is actually hollow so air goes through (figure 2) and therefore I can't use the tutorial (mainly because they don't end at the same plane). Do you have any suggestion as to a meshing strategy for this region? I've meshed the rest of the aircraft and this is my last problem. I'm thinking of removing the turbine and the bottom part of the nacelle because it adds unnecessary complexity (I think I could live with the missing parts especially when setting up the boundary conditions). That's why I wanted to split the model (and the winglets came off).

I would really appreciate it if you could offer a piece of advice.


Lefteris


Update

Well, I deleted the turbine and the bottom of the pylon, tried to reassemble the whole model and this time the winglets were added. It seems rather random because I didn't do anything different... only the tolerance was difference but much much smaller!
Attached Images
File Type: jpg model_surfaces.jpg (26.7 KB, 16 views)
File Type: jpg engine.jpg (22.6 KB, 15 views)
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Last edited by Aeronautics El. K.; July 13, 2014 at 19:08. Reason: update
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Old   July 14, 2014, 09:47
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Chris Sideroff
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This definitely sounds like some weird behavior. Glad to hear you've got it working.

Quote:
Originally Posted by Aeronautics El. K. View Post
Each time I used different tolerances in order to get the model assembled.
A clarification here. Only a single tolerance is used within a model. Applying one tolerance at one point and then another tolerance later means the actual tolerance used for each piece of the entire model is the last one.

Just to be clear here's a silly analogy. You have 5 pieces of wood you want to glue into one. You glue the first two together with red colored glue. Then glue the third piece to first two with blue glue. The fourth to the three with green glue. And the fifth to the four with white glue. The final assembly does have not red, blue, green and white glue but _only_ white.

It sounds strange but the reason it's like this is because every time you add a piece it's essentially re-assembling the whole model.
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Old   July 14, 2014, 10:45
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Lefteris
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Ah, I see! It's good that you made this clarification and set this straight.
Initially I thought that as long as I put some parts together they will be fixed with each other irrespectivelly of the tolerance I use later to add more (sub-) models.
Lesson learnt then: The last tolerance is applied to the whole model.

Thanks Chris!
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