[Gmsh] Gmsh: 3D Volume with a hole (not through-going)
Omid Mahabadi
omid.mahabadi at geomechanica.com
Wed Sep 3 00:10:16 CEST 2014
Hi Oliver,
You seem to be right and I may have to follow the approach that I didn't
want to pursue initially: manually adding most of the entities.
Thanks,
Omid
On 14-09-02 05:57 PM, Oliver Willekens wrote:
> If you change the lines in your file after ```//Using compound
> volumes``` to the ones from my previous mail, you should get the same
> result.
> From the looks of your screenshot, it would seem the bottom half is
> not defined as a volume. I got it automatically as a volume though,
> from the extrusion command. Odd.
>
> After my first reply, I've looked more into those GRegion Compound
> errors, and have seen that they're a recurring problem on the mailing
> list when trying to use Compound Volume, but so far no solutions have
> been given/found. I'm hoping an answer will come one day though.
>
> The only other solution I see (at the moment, due to the failing
> compound volumes) to ensure the mesh is "continuous" across the
> interface, is simply not to have the interface at all. So manually
> fleshing out the geometry, point by point, line by line (okay, you can
> extrude some points and lines of course) and then definining a single
> volume by selecting the faces of the cylinder and the box. So this
> comes back to your original question:
> >> I know I can define all the surfaces, surface loops, and volumes
> manually, but is there a better way of defining something like this in
> Gmsh?
> At the moment: no. Unless you don't mind that artificial interface.
>
>
> 2014-09-02 21:13 GMT+02:00 Omid Mahabadi
> <omid.mahabadi at geomechanica.com <mailto:omid.mahabadi at geomechanica.com>>:
>
> Hi Oliver,
> Thanks for your response. I had also tried the variation that you
> sent me. The issue is that I don't want to have the flat surface
> that is interfacing the two volumes. I'd like the mesh to be
> continuous across that interface.
>
> Also, when following your suggestion, I still cannot get the same
> exact mesh as you did. Please see the attached screenshot.
>
> Is there any other thoughts on how to get the results I'm aiming for?
>
> Thank you,
> Omid
>
>
> On 14-08-28 06:34 PM, Oliver Willekens wrote:
>>
>> You could delete the volume of the cylinder you’ve created by
>> means of extrusion and then delete one of the cylinder’s flat
>> surfaces using the |Delete| command. However, it won’t give you
>> what you want, because the box “holding the cylinder” will be
>> unaware of the presence of the cylindrical hole.
>>
>> I tried this:
>>
>> |Plane Surface(1) = {1, 2}; // square minus the circle
>> out1[] = Extrude {0.0, 76.2, 0.0}{Surface{1};};
>> Plane Surface(2) = {1};
>> out2[] = Extrude {0.0, -76.2, 0.0} {Surface{2};};
>> |
>>
>> Which results in the 2D mesh you find in the attachment. Perhaps
>> this is what you’re looking for?
>>
>> I also tried combining those two volumes using |Compound
>> Volume(4) = {out1[1], out2[1]};|, but like you, I got GRegion
>> Compound errors. Probably some basic restriction from
>> triangulations I’m overlooking. This only means your 3D meshes
>> will be clearly stopped at a flat interface about half-way
>> through those two boxes, but you’ll still have a 3D mesh. I was
>> hoping that the Compound Volume would make some tetras across
>> this boundary though… But with the above lines, you’ll have a
>> working mesh.
>>
>>
>>
>>
>> 2014-08-28 17:08 GMT+02:00 Omid Mahabadi
>> <omid.mahabadi at geomechanica.com
>> <mailto:omid.mahabadi at geomechanica.com>>:
>>
>> Hi Christophe and Gmsh team,
>> I've been trying to model a simple cube with a cylindrical
>> hole that is NOT through-going (i.e., its depth is smaller
>> than the depth of the cube), as shown in the attached
>> picture. The Extrude command doesn't seem to work since it
>> will extrude both surfaces (exterior and interior -- hole) at
>> the same time. I know I can define all the surfaces, surface
>> loops, and volumes manually, but is there a better way of
>> defining something like this in Gmsh?
>>
>> I also tried to use the Compound Volume command by first
>> defining two volumes from Extrude and then trying to combine
>> them but I'm getting errors for the Compound Volume
>> visualization (Error: Cannot evaluate bounds on GRegion
>> Compound) and when I mesh the geometry, the actual shared
>> interfaces are still existing, although by the notion of
>> compound from the documentation, the internal interfaces
>> should be neglected. Here is the geometry file:
>>
>> // Characteristic length (==> element size)
>> cl_external = 25;
>> cl_excavation = 5;
>>
>> // External boundaries
>> Point(1) = {-127, 0.0, -127, cl_external};
>> Point(2) = {+127, 0.0, -127, cl_external};
>> Point(3) = {+127, 0.0, +127, cl_external};
>> Point(4) = {-127, 0.0, +127, cl_external};
>> Line(1) = {1, 2};
>> Line(2) = {2, 3};
>> Line(3) = {3, 4};
>> Line(4) = {4, 1};
>> Line Loop(1) = {1, 2, 3, 4};
>>
>> // Excavation boundaries
>> Point(5) = {0.0, 0.0, 0.0, cl_excavation};
>> Point(6) = {19.05, 0.0, 0.0, cl_excavation};
>> Point(7) = {0.0, 0.0, 19.05, cl_excavation};
>> Point(8) = {-19.05, 0.0, 0.0, cl_excavation};
>> Point(9) = {0.0, 0.0, -19.05, cl_excavation};
>> Circle(5) = {6, 5, 7};
>> Circle(6) = {7, 5, 8};
>> Circle(7) = {8, 5, 9};
>> Circle(8) = {9, 5, 6};
>> Line Loop(2) = {5, 6, 7, 8};
>>
>> //Using compound volumes
>> Plane Surface(1) = {1};
>> out1[] = Extrude {0.0, 76.2, 0.0}{Surface{1};};
>>
>> Plane Surface(2) = {1};
>> out2[] = Extrude {0.0, -76.2, 0.0}{Surface{2};};
>>
>> Compound Volume(3) = {1, 2};
>>
>>
>> I also tried to create the geometry in CAD software and
>> imported it as iges, brep or step formats but for reason the
>> hole is not there completely. See for instances the iges file
>> attached.
>>
>> Can you kindly shed some light here? Am I doing something
>> wrong? Or are there Gmsh tricks/commands that I can use to
>> achieve my goal?
>>
>> Thank you,
>> Omid
>>
>> --
>> Omid Mahabadi, Ph.D.
>> Geomechanica, Inc.
>> http://www.geomechanica.com/
>> Tel :+1-647-478-9767 <tel:%2B1-647-478-9767>
>> Cell:+1-416-824-2408 <tel:%2B1-416-824-2408>
>>
>>
>> _______________________________________________
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>> gmsh at geuz.org <mailto:gmsh at geuz.org>
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>>
>>
>>
>>
>> --
>> Oliver Willekens
>> PhD Student
>> LCP group logo <https://lcp.elis.ugent.be/>
>>
>> Liquid Crystals & Photonics Group
>> Sint- Pietersnieuwstraat 41
>> 9000 Gent
>> Phone: +32 9 264.89.51 <tel:%2B32%209%20264.89.51>
>>
>
> --
> Omid Mahabadi, Ph.D.
> Geomechanica, Inc.
> http://www.geomechanica.com/
> Tel :+1-647-478-9767 <tel:%2B1-647-478-9767>
> Cell:+1-416-824-2408 <tel:%2B1-416-824-2408>
>
>
>
>
> --
> Oliver Willekens
> PhD Student
> LCP group logo <https://lcp.elis.ugent.be/>
>
> Liquid Crystals & Photonics Group
> Sint- Pietersnieuwstraat 41
> 9000 Gent
> Phone: +32 9 264.89.51
>
--
Omid Mahabadi, Ph.D.
Geomechanica, Inc.
http://www.geomechanica.com/
Tel : +1-647-478-9767
Cell: +1-416-824-2408
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