> On 4 Apr 2019, at 03:32, Gavin Ridley <[email protected]> wrote:
>
> Unfortunately I cannot share this STEP file in particular. It's a bit big for
> sake of example anyways. Even better, could you show how to modify import.geo
> from the demos directory so that the cylindrical surface on the inside of the
> nut is split into two cylinders by a plane perpendicular to the axis of the
> nut's hole? Then one BC could be applied below a certain axial level (along
> the axis of the nut's hole) and a separate one above that plane?
>
> Physically, I need to do this since I'm trying to model a pipe which has one
> section of it wrapped in heating tape, and another section insulated.
>
> If this isn't straightforward, I will just go back and modify the CAD. Seems
> that most CAD software has a tool for splitting surfaces.
>
Sure - you can use boolean operations:
SetFactory("OpenCASCADE");
Cylinder(1) = {0.5,0.5,-0.5, 0,0,1, 0.1};
Rectangle(100) = {0,0,0,1,1,0};
BooleanFragments{ Volume{1}; Delete; }{ Surface{100}; Delete; }
Christophe
> On Wed, Apr 3, 2019 at 4:13 PM <[email protected]> wrote:
>
>
> Le 3 avr. 2019 à 21:51, Gavin Ridley <[email protected]> a écrit :
>
>> Hi Dr. Geuzaine,
>>
>> Thanks for your response. I see the problem here now. It doesn't work after
>> meshing, although the geometry seems to load to the GUI. Unfortunately, I
>> need to split a surface into two surfaces, and it seems there's no way to do
>> that to the STEP file using what's available under the OpenCASCADE kernel
>> right now.
>
> Can you share the STEP file? It should be possible to do what you want
> directly in Gmsh.
>
>
>> I was hoping to be able to convert the STEP to gmsh-style geometry, then
>> delete a surface (and its dependent volumes) and replace it with a new,
>> split one. I'll just have to change the CAD then re-export, I suppose.
>>
>> Thanks again!
>>
>> On Wed, Apr 3, 2019 at 3:11 PM Christophe Geuzaine <[email protected]>
>> wrote:
>>
>>
>> > On 3 Apr 2019, at 18:23, Gavin Ridley <[email protected]> wrote:
>> >
>> > Hi,
>> >
>> > I would just like to note something to the developers regarding a perhaps
>> > unnecessary skipping of surfaces in the code.
>> >
>> > I recently have had to convert a STEP file with fairly complicated
>> > geometry to a GEO.
>>
>> Don't do that. By design, Gmsh never translates from one CAD format to
>> another. The "unrolled GEO" feature is there for unrolling complex GEO
>> scripts. It can indeed export a limited subset of geometrical entities
>> created by other CAD kernels, but it's there only for debugging.
>>
>> If you want to modify a STEP model, set
>>
>> SetFactory("OpenCASCADE");
>>
>> at the beginning of your script. Since we import STEP models with
>> OpenCASCADE, this will allow you to modify the file directly with
>> OpenCASCADE. See
>> https://gitlab.onelab.info/gmsh/gmsh/blob/master/demos/boolean/import.geo
>> for an example.
>>
>> Christophe
>>
>>
>>
>>
>> > This is done so that I can split one of the surfaces in the STEP file to
>> > set different BCs on different parts of the surface. At the moment, it
>> > appears that gmsh will skip several surfaces in the conversion from STEP
>> > to geo_unrolled unnecessarily: surfaces were left out from the gmsh file.
>> > A warning message comes with this.
>> >
>> > It seems, however, that the skipped surfaces work fine if you just go back
>> > in and add surfaces manually. Gmsh now reads the geo file correctly.
>> >
>> > So, why are these surfaces being skipped? Is there some ambiguity about
>> > their interpretation from STEP? It would be nice to not have to manually
>> > go in and add the surfaces.
>> >
>> > --
>> > Thanks,
>> > Gavin Ridley
>> > _______________________________________________
>> > gmsh mailing list
>> > [email protected]
>> > http://onelab.info/mailman/listinfo/gmsh
>>
>> —
>> Prof. Christophe Geuzaine
>> University of Liege, Electrical Engineering and Computer Science
>> http://www.montefiore.ulg.ac.be/~geuzaine
>>
>>
>>
>>
>>
>> --
>> Thanks,
>> Gavin Ridley
>
>
> --
> Thanks,
> Gavin Ridley
—
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine
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