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Old   March 27, 2003, 00:44
Default Problem of importing the geometry
  #1
Dany
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Hi everyone,

I have created the model surface in the CAD software and then imported the iges file to CFX5 so that I can create a B-rep solid in the build. However, I found out later that lots of problems occurred when it came to meshing:

1. The mesh doesn't follow exactly the goemetry boundary (esp along the curved surface) if you view it from the Post.

2. Sharp edge & small angle.

The model looks fine in the build. Someone suggests to me that creating & importing a solid rather than a set of surfaces from the CAD may help solving the problem. I don't actually see the difference between these options(ie. creating B-rep from set of imported surfaces & solid).

I have been struggling to overcome this problem for months. Could anyone please give me some advices before I try this approach? Any comments are very welcomed. Thanks.
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Old   March 27, 2003, 06:42
Default Re: Problem of importing the geometry
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Helper
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The meshing tools in Build can only place mesh vertices on the surface of the geometry. The mesh displayed in Post is facetted and will not appear smooth like the surfaces/curves shown in Build, i.e. the edges between vertices are straight and not curved like the geometry. If you produce a finer mesh, it should give a closer approximation to the geometry.

The surface meshing is patch based and therefore any sharp edges or small angle will produce surface triangles with acute angles.
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Old   March 27, 2003, 10:03
Default Re: Problem of importing the geometry
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Dany
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Thanks for your answer, Helper. If the mesh displayed in the Post is not as smooth as the one in the Build, the mesh should be refined again. Is that the message that you're trying to deliver? I set the mesh using relative error with the same max/min edge length. Will that be the reason of this problem?

Besides, do you have any thought about the method of importing the solid rather than the multiple surfaces from the CAD? Will the Build view the CAD solid as a single surface and can this improve the small angle problem?

Thanks for all the advices here.
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Old   March 28, 2003, 06:48
Default Re: Problem of importing the geometry
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Helper
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The mesh viewed in Post and Build should be the same. If it is not, then something strange has happened. What I am saying is that the mesh is an approximation of the geometry and displays straight lines between mesh vertices. If the geometry has high curvature then the mesh will look like a poor approximation, refining the mesh in that area using "angular resolution" or "relative error" will improve the approximation, but you should NOT have the same min/max values, the min value should be at least one order of magnitude smaller than the max (preferably two orders). Setting the same min/max is not a good idea.

The imported geometry should be the same for a solid and a set of surfaces changed into a solid. The small angle could be improved using the surface merging capability, but will only help if the small angle is not a significant feature of the geometry.
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Old   March 28, 2003, 10:49
Default Re: Problem of importing the geometry
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Dany
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Thanks again, Helper. I get a much better idea right now.
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