[Gmsh] Gmsh: 3D Volume with a hole (not through-going)
Omid Mahabadi
omid.mahabadi at geomechanica.com
Wed Sep 3 00:09:03 CEST 2014
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.brady at gmail.com 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 <javascript:>>:
>>
>> 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
>>
>>
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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
>>
>
> --
> 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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