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
<[email protected]
<mailto:[email protected]>>:
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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