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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Convert to solid of parametric surfaces

Posted 2012年7月27日 GMT-4 07:29 Geometry, Parameters, Variables, & Functions Version 4.3 4 Replies

Maximilian Harmel
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I tried to create a cube by converting 6 surfaces to a solid. 5 surfaces are just plane, and the one at the top has a roughness, which is determined by interpolating from a data (701x701 points). The top surface is only rough in the middle part, so area around the border has the same z-coordinate than the border of the side surfaces. The interpolation results in a warning, because the maximum relative error is about 0.0045. When I want to convert the surfaces to a solid comsol give me the error message ' internal error in geometric decomposition'. If I increase the relative repair tolerance, the solid will convert, but its so unexact that the roughness disappears and it is just another plane surface.

It would be really nice, if somebody of you could give me some hints how to decrease the relative error from interpolating or some other ideas so the convertion can be done. The distance between two points of the rough surface is 1 m, so the cube has a edge length of 0.7mm. Are this still not enough points to interpolate more exactly?
4 Replies Last Post 2012年7月27日 GMT-4 09:42
Maximilian Harmel
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Posted: 1 decade ago 2012年7月27日 GMT-4 07:31
here is the comsol modell file!
here is the comsol modell file!

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John H.
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Posted: 1 decade ago 2012年7月27日 GMT-4 08:59
For what it's worth, if you use the geometry kernel that ships with any of the CAD import modules instead of Comsol's standard geometry kernel, your geometry sequence works as it is.
For what it's worth, if you use the geometry kernel that ships with any of the CAD import modules instead of Comsol's standard geometry kernel, your geometry sequence works as it is.
Maximilian Harmel
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Posted: 1 decade ago 2012年7月27日 GMT-4 09:20
thanks very much for your help. I used the comsol kernel because we have only a limited number of cad import licences. The solid is still just converted with a reapir tolerance > 1.5 E-4 . Is this a problem or can i ignore this? in the end, two of this cubes should be pressed together at their rough surfaces!
thanks very much for your help. I used the comsol kernel because we have only a limited number of cad import licences. The solid is still just converted with a reapir tolerance > 1.5 E-4 . Is this a problem or can i ignore this? in the end, two of this cubes should be pressed together at their rough surfaces!
John H.
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Posted: 1 decade ago 2012年7月27日 GMT-4 09:42
The solid is still just converted with a reapir tolerance > 1.5 E-4 . Is this a problem or can i ignore this?

I don't know for sure. (I also don't think anybody *really* knows what these geometry kernels do internally.) As long as it works, I usually don't worry about it much. I'm guessing that in your case you need to relax the repair tolerance so that the edges match. (Even though you said the top surface is only rough in the middle, maybe the interpolation routine causes some trouble here...)

Anyway, if the high tolerance bothers you, there's another way to achieve the same result. Make a block that extends from below to above your rough surface, but has otherwise the same dimensions. Then unite block and surface, split, and delete the "outside" part. This way, you get the job done with the standard repair tolerance of 1e-6. But again, it only works with the CAD kernel, not the standard one.

in the end, two of this cubes should be pressed together at their rough surfaces!

Good luck with that. You'll certainly need it.
[quote]The solid is still just converted with a reapir tolerance > 1.5 E-4 . Is this a problem or can i ignore this?[/quote] I don't know for sure. (I also don't think anybody *really* knows what these geometry kernels do internally.) As long as it works, I usually don't worry about it much. I'm guessing that in your case you need to relax the repair tolerance so that the edges match. (Even though you said the top surface is only rough in the middle, maybe the interpolation routine causes some trouble here...) Anyway, if the high tolerance bothers you, there's another way to achieve the same result. Make a block that extends from below to above your rough surface, but has otherwise the same dimensions. Then unite block and surface, split, and delete the "outside" part. This way, you get the job done with the standard repair tolerance of 1e-6. But again, it only works with the CAD kernel, not the standard one. [quote]in the end, two of this cubes should be pressed together at their rough surfaces![/quote] Good luck with that. You'll certainly need it.

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