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Geometry Creation and Union Function

Posted Mar 1, 2011, 10:51 a.m. EST Geometry Version 4.1 3 Replies

Melanie Pigeon
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Hi!
I am tryignt o create a model to simulate fluid flow in a pipe. The pipe have a number of twists and turns. I recreated the problem in COMSOL but my problem is that everytime I try to create a union is tells me 'Internal error in geometry decomposition'. All of the segments were created using the work place and revolve tools. The only problem I can think of is that the pipe diameters/segments aren't perfectly aligned. Any advice on how I can solve this problem without having to redo my entire model?
Cheers,
Melanie
3 Replies Last Post Mar 1, 2011, 3:59 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 1, 2011, 11:02 a.m. EST
Hi

you need a "clean" geometrical model, otherwise you will have problems with the mesh.

For complex CAD I prefer a dedicated tool like SolidWorks.

One way in COMSOL is to let the geometries penetrate and you make differences to cut them and obtain clean joints.

Then at the end you might form a or several unions (with or without) the internal boundaries. Note that if your domain is unique and loops around the mesher might have problems to find a solution. I often leave clean internal boundaries to allow me to better mesh be segments, manually. the nice thing is that in 4.1 you can rebuild and adapt your CAD and mesh generation rather easily

--
Good luck
Ivar
Hi you need a "clean" geometrical model, otherwise you will have problems with the mesh. For complex CAD I prefer a dedicated tool like SolidWorks. One way in COMSOL is to let the geometries penetrate and you make differences to cut them and obtain clean joints. Then at the end you might form a or several unions (with or without) the internal boundaries. Note that if your domain is unique and loops around the mesher might have problems to find a solution. I often leave clean internal boundaries to allow me to better mesh be segments, manually. the nice thing is that in 4.1 you can rebuild and adapt your CAD and mesh generation rather easily -- Good luck Ivar
Melanie Pigeon
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Posted: 1 decade ago Mar 1, 2011, 11:16 a.m. EST
I just tried using the difference tool and it will not let me perform the operation. Once again the error is 'Internal error in geometry decomposition'.
Thanks for the help!
I just tried using the difference tool and it will not let me perform the operation. Once again the error is 'Internal error in geometry decomposition'. Thanks for the help!
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Mar 1, 2011, 3:59 p.m. EST
Hi

still one more thing to check, if your geoemtry is small (10um or less) you should check the relative repair tolerance of your geoemtry (w.r.t units used), and ensure it's at least 10 times smaller than the smallest feature you have, this might limit the sizes of resulting geometries and produce errors

--
Good luck
Ivar
Hi still one more thing to check, if your geoemtry is small (10um or less) you should check the relative repair tolerance of your geoemtry (w.r.t units used), and ensure it's at least 10 times smaller than the smallest feature you have, this might limit the sizes of resulting geometries and produce errors -- Good luck Ivar

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