[Gmsh] Gmsh: 3D Volume with a hole (not through-going)

Omid Mahabadi omid.mahabadi at geomechanica.com
Wed Sep 3 20:04:28 CEST 2014


Hi Errol,
This is exactly what I wanted. Did Solidworks automatically find and 
correct the errors? Do you have any other suggestions for modifying the 
iges files?

Thanks,
Omid

On 14-09-03 01:03 PM, erroll.brady at gmail.com wrote:
> Hi Omid,
> Try the attached Block2.zip.
>
> Erroll
>
> <https://lh5.googleusercontent.com/-EkE2FS91LsI/VAdJvqh3QUI/AAAAAAAAAAw/pfpGUvqDVdQ/s1600/Block2.jpg>
>
>
>
> On Tuesday, September 2, 2014 9:39:45 PM UTC-7, Omid Mahabadi wrote:
>
>     Hi Errol,
>     In the version you sent me, the hole is through-going, in other
>     words, it goes through the entire depth of the cube (along z).
>     However, my desired geometry requires a hole that doesn't go
>     through the entire depth (say it has half of the depth of the
>     exterior cube).
>
>     Thank you,
>     Omid
>
>
>     On 14-09-02 06:04 PM, erroll... at gmail.com <javascript:> wrote:
>>     Hello Omid,
>>     Solidworks found errors in your IGES file. Try the attached STEP,
>>     GEO and MSH files.
>>
>>     <https://lh4.googleusercontent.com/-nxF0eT1U3qQ/VAY-5mA30KI/AAAAAAAAAAg/aQ6Sqk53Fp8/s1600/Block%2BMesh.jpg>
>>
>>
>>     Erroll
>>
>>     On Tuesday, September 2, 2014 1:28:00 PM UTC-7, Omid Mahabadi wrote:
>>
>>         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.m... 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
>>>             Cell:+1-416-824-2408
>>>
>>>
>>>             _______________________________________________
>>>             gmsh mailing list
>>>             gm... at geuz.org
>>>             http://www.geuz.org/mailman/listinfo/gmsh
>>>             <http://www.geuz.org/mailman/listinfo/gmsh>
>>>
>>>
>>>
>>>
>>>         -- 
>>>         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
>>
>
>     -- 
>     Omid Mahabadi, Ph.D.
>     Geomechanica, Inc.
>     http://www.geomechanica.com/
>     Tel : +1-647-478-9767
>     Cell: +1-416-824-2408
>

-- 
Omid Mahabadi, Ph.D.
Geomechanica, Inc.
http://www.geomechanica.com/
Tel : +1-647-478-9767
Cell: +1-416-824-2408

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