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Different number of mesh cells

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Old   September 11, 2017, 03:09
Default Different number of mesh cells
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Daniel
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Hi,

I've been trying to run a reliance test on different CAD modelling software (Rhino and Maxsurf) on my CFD project. I would draw up a simple box with a raked bow (a chamber at the front bottom edge) with same dimensions in the CAD software and export the following as Parasolids (.x_t files). I did the same with the CAD software in Star-CCM+ and export it as a Parasolid and importing it again to ensure there was no variation in the file type. After I set up each file with similar mesh properties (same size, same type, same model, everything), The total number of cells would be different for each type of model even if they had the same dimensions. Is there an explanation for this or am I doing something wrong?

P.S. I've ran the process a couple of times and still got the same result.
Thanks.
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Old   September 11, 2017, 05:45
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first check your cad from each source is actually identical in all ways including position and coplanar surfaces eg by importing each into 3d-cad and comparing each surface or can be done in as parts import too - if not then you will get different cell numbers.
then ensure you have the surface remesher enabled in so you have identical remeshed surfaces triangles to base the volume mesh on - again take a close look at these and compare local triangle sizes between cads.
you can do all the meshing in one case model of course by using the different imported or 3d-cad part in turn in the one mesh operation so ensuring you do have identical mesh settings.
you might see a minor difference in cell numbers but nothing large when the above steps are followed.
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Old   September 19, 2017, 20:16
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Quote:
Originally Posted by ping View Post
first check your cad from each source is actually identical in all ways including position and coplanar surfaces eg by importing each into 3d-cad and comparing each surface or can be done in as parts import too - if not then you will get different cell numbers.
then ensure you have the surface remesher enabled in so you have identical remeshed surfaces triangles to base the volume mesh on - again take a close look at these and compare local triangle sizes between cads.
you can do all the meshing in one case model of course by using the different imported or 3d-cad part in turn in the one mesh operation so ensuring you do have identical mesh settings.
you might see a minor difference in cell numbers but nothing large when the above steps are followed.
Thanks Ping! I did what you said and the cell difference dropped by a lot to about 20 apart. Since it has around 500k cells, i think that difference is acceptable. Still having some difficulties with the CAD surfaces when I import them from Maxsurf.
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Old   September 19, 2017, 21:52
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maxsurf does create surfaces that dont import well occasionally so the way i have cured this is to import into rhino 4 and then tessellate in there during the save i think and this cures most issues but you might still need to zip some edges and fill a hole or two
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cad import, mesh 3d, number of cells, star ccm +geometry, star ccm+ help

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