[Gmsh] Gmsh: 3D Volume with a hole (not through-going)
erroll.brady at gmail.com
erroll.brady at gmail.com
Wed Sep 3 00:04:51 CEST 2014
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
>>
>>
>> _______________________________________________
>> gmsh mailing list
>> gm... at geuz.org <javascript:>
>> http://www.geuz.org/mailman/listinfo/gmsh
>>
>>
>
>
> --
> Oliver Willekens
> PhD Student
> [image: 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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