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

erroll.brady at gmail.com erroll.brady at gmail.com
Wed Sep 3 19:03:37 CEST 2014


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