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Surface is Mesh is not what was expected

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Old   March 10, 2017, 10:22
Default Surface is Mesh is not what was expected
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Hello everyone.

I am trying to mesh the interior of a car using a volumentric control aroundthe windscreen. However, the mesh that I get later in a mesh scene is far away from what I would expect. Only a fraction of the overall car is meshed (left part of the dashboard). What can be the cause for it and how can I fix this?
Star-CCM+ is able to mesh the entire region only with one particular combination of settings. However, those settings create a far too rough mesh and is not acceptable in any way. As soon as I change either the volumetric control or the simple base size of the mesh, it does not mesh the whole region any longer.
I hope someone can help me with that.
Thanks in advance.
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Old   March 10, 2017, 10:25
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It sounds like you have some kind of setup or geometry problem. Can you post pictures of your geometry, mesh, and settings?

Are you using the wrapper?
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Old   March 10, 2017, 10:46
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Quote:
Originally Posted by me3840 View Post
It sounds like you have some kind of setup or geometry problem. Can you post pictures of your geometry, mesh, and settings?

Are you using the wrapper?
Here are pictures of the model and mesh that "works" and the mesh which is just completely weird. I worked a day on it trying to make it work.

Mesh Settings:
  • Models:
  1. Polyhedral Mesher
  2. Prism Layer Mesher
  3. Surface Remesher
  4. Surface Wrapper
  • Reference Values:
  1. Base Size: 10 mm (it works with 50 mm)
  2. Automotic Surface Repair: Default
  3. Cad Projection: Default
  4. Number of Prism Layers: 10
  5. Prism Layer Stretching
  6. Prism Layer Thickness: Relative 25%
  7. Surface Curvature: Default
  8. Surface Growth Rate: Default
  9. Surface Proximity: Default
  10. Surface Size: Default
  11. Tet/Poly Density: Default
  12. Tet/Boly Volume Blending: 0.3
  13. Wrapper Feature Angle: Default
  14. Wrapper Scale Factor: 80 %
For the Volumetric Control I refined all models and refined the size with 5%, 20 prism layers, 1.5 prism layer stretching, and 30 % prism layer size.

I have everything in a single region. Those are the settings that I want to have. But keeping everything the same and changing the base size completely messes up the entire model.

I need to use the wrapper, because the model as a few openenings, that I want to be closed.
Attached Images
File Type: jpg 1.JPG (47.7 KB, 62 views)
File Type: jpg 2.JPG (44.1 KB, 55 views)
File Type: jpg 3.JPG (51.5 KB, 52 views)
File Type: jpg WorkinSetting.JPG (109.5 KB, 60 views)
File Type: jpg NotExpected.JPG (89.7 KB, 52 views)
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Old   March 10, 2017, 11:07
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Okay, this makes more sense.

You are using the region-based wrapper. This utility is a little older and has the caveat that your mesh settings change the wrap, which is not always desirable, as you're seeing here.

In your coarse mesh that only refines part of the dashboard, the wrap is coarse enough so that it seals everywhere inside of that part, and that's what you get output. When you refine the mesh, you allow the wrap to 'leak' through cracks in your geometry, which causes you to get what you see here.

I would recommend you switch to the parts-based wrapper so that your mesh settings do not impact your wrap, and go through the wrapping tutorials so you understand how it works.

Also there are a lot of gaps in the geometry. Even though the wrapper creates closed surfaces, it's not magic, and putting some effort in cleaning up the surface is well worth the time spent. These can be just patches, since you're wrapping, you don't have to put a lot of effort into it.
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Old   March 15, 2017, 08:38
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Quote:
Originally Posted by me3840 View Post
Okay, this makes more sense.

You are using the region-based wrapper. This utility is a little older and has the caveat that your mesh settings change the wrap, which is not always desirable, as you're seeing here.

In your coarse mesh that only refines part of the dashboard, the wrap is coarse enough so that it seals everywhere inside of that part, and that's what you get output. When you refine the mesh, you allow the wrap to 'leak' through cracks in your geometry, which causes you to get what you see here.

I would recommend you switch to the parts-based wrapper so that your mesh settings do not impact your wrap, and go through the wrapping tutorials so you understand how it works.

Also there are a lot of gaps in the geometry. Even though the wrapper creates closed surfaces, it's not magic, and putting some effort in cleaning up the surface is well worth the time spent. These can be just patches, since you're wrapping, you don't have to put a lot of effort into it.


Thanks for your help and advise. I finally get in the direction that I'm aiming for.
Now I succeeded to create a Surface Mesh. However, I started to face a new problem which concerns the volume mesh. After about ten seconds of volume meshing, the service aborts saying that there are still self intersecting faces. After wrapping though, the output window displayed that there are no remaining self-intersections. How can that be fixed without knowing, where those self intersections occur?


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Old   March 15, 2017, 19:56
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This means that there are errors in the surface remesher's output. Do you have automatic surface repair enabled?

You can check where the faces are by loading the remeshed surface into surface repair.
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Old   March 23, 2017, 06:34
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I managed to fix all my problems now. Thanks for your help!


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