[Gmsh] Problem with mesh over extruded surface where other surfaces are defined

Thu Feb 7 10:49:47 CET 2019

Thank you for your fast reply!

With respect to the bottom part, when I plot only the Physical Surfaces 98,
99 and 100 (they correspond to the Plane Surfaces 26, 46 and 47), I do not
see any visible overlap. Plane 47 is indeed the one with holes, while
Planes 26 and 46 are the surfaces of the holes. Those holes are where I
will apply boundary conditions. Am I missing something?

When I add BooleanFragments{ Surface{:}; Delete; }{ Volume{:}; Delete; } at
the end of the file, I get a syntax errors, I suspect it's because I use an
old gmsh version: 3.0.5. I'll retry on the latest version.

With respect to 1), how would you do it? In other words, what did I do
"wrong" or more complicated than it should be?

With respect to 2), when I remove Layers{15};, all the surfaces seem
correctly meshed! But I am probably overlooking something... In any case, I
wish to have a high mesh resolution along the z-axis direction, I thought
that specifying Layers{}; was the simplest way to go for that. How could I
do it if I remove the Layers{}; command?

On Thu, Feb 7, 2019, 08:34 Christophe Geuzaine <cgeuzaine at uliege.be wrote:

>
>
> > On 6 Feb 2019, at 23:14, Isaac Haïk Dunn <anjeeisaac at gmail.com> wrote:
> >
> > Hello,
> > My goal is to create a parallelepiped with two rectangles on each of the
> top and bottom surfaces. That way I could import the mesh and solve an
> equation on that volume and apply boundary conditions on each of the 4
> rectangular regions over the solid.
> >
> > I've almost completed the task by extruding a rectangular shape and by
> defining the rectangles over the top and bottom surfaces. However when I
> mesh 3D, the bottom surface and the volume are correctly meshed, but not
> the top surface. The mesh does not accommodate to the two rectangular
> shapes, hence my final mesh over that surface has two meshes overlapping on
> each rectangle, which is a problem.
> > I applied the exact same logic than for the bottom surface, so I do not
> really understand why the result differs, nor how I could fix it. I would
> greatly appreciate some guidance!
> >
>
> Even for the bottom part, you have defined overlapping surfaces. Only
> surface 47 is correctly defined with holes...
>
> You can "fragment" everything, i.e. add
>
>    BooleanFragments{ Surface{:}; Delete; }{ Volume{:}; Delete; }
>
> add the end of your file to fix the mess, but
>
> 1) it would clearly be better to define everything correctly in the first
> place
> 2) you won't be able to use structured meshing commands in the extrusion
> (i.e. you have to remove "Layers ..." in Extrude)
>
> Christophe
>
> > Here's the code:
> >
> > SetFactory("OpenCASCADE");
> > Mesh.RandomFactor=1.0e-6;
> > lc=0.35;
> > a = 2;
> > b = 1;
> > c = 0.06;
> >
> > // bottom motif
> > Point(1) = {-a/2, -b/2, -c/2, lc};
> > Point(2) = {-a/2, b/2, -c/2, lc};
> > Point(3) = {a/2, b/2, -c/2, lc};
> > Point(4) = {a/2, -b/2, -c/2, lc};
> > Line(1) = {1,2};
> > Line(2) = {2,3};
> > Line(3) = {3,4};
> > Line(4) = {4,1};
> > Line Loop(5) = {1,2,3,4};
> > Plane Surface(6) = {5};
> >
> > // auxiliary points over top and bottom surface
> > // rectangle 1
> > Point(7) = {-a/10 + a/4.4,-b/10, c/2};
> > Point(8) = {-a/10 + a/4.4,b/10,c/2};
> > Point(9) = {a/10 + a/4.4, b/10,c/2};
> > Point(10) = {a/10 + a/4.4,-b/10,c/2};
> > Line(11) = {7,8};
> > Line(12) = {8,9};
> > Line(13) = {9,10};
> > Line(14) = {10,7};
> > Line Loop(15) = {11,12,13,14};
> > Plane Surface(16) = {15};
> >
> > // rectangle 2
> > Point(17) = {-a/16+a/4,-b/16, -c/2};
> > Point(18) = {-a/16+a/4,b/16,-c/2};
> > Point(19) = {a/16+a/4, b/16,-c/2};
> > Point(20) = {a/16+a/4,-b/16,-c/2};
> > Line(21) = {17,18};
> > Line(22) = {18,19};
> > Line(23) = {19,20};
> > Line(24) = {20,17};
> > Line Loop(25) = {21,22,23,24};
> > Plane Surface(26) = {25};
> >
> > // rectangle 3
> > Point(27) = {-(-a/16+a/4),-b/16, c/2};
> > Point(28) = {-(-a/16+a/4),b/16,c/2};
> > Point(29) = {-(a/16+a/4), b/16,c/2};
> > Point(30) = {-(a/16+a/4),-b/16,c/2};
> > Line(31) = {27,28};
> > Line(32) = {28,29};
> > Line(33) = {29,30};
> > Line(34) = {30,27};
> > Line Loop(35) = {31,32,33,34};
> > Plane Surface(36) = {35};
> >
> > // rectangle 4
> > Point(37) = {-a/22+a/14,-b/22, -c/2};
> > Point(38) = {-a/22+a/14,b/22,-c/2};
> > Point(39) = {a/22+a/14, b/22,-c/2};
> > Point(40) = {a/22+a/14,-b/22,-c/2};
> > Line(41) = {37,38};
> > Line(42) = {38,39};
> > Line(43) = {39,40};
> > Line(44) = {40,37};
> > Line Loop(45) = {41,42,43,44};
> > Plane Surface(46) = {45};
> >
> >
> > // bottom mesh
> > Line Loop(46) = {2, 3, 4, 1};
> > Line Loop(47) = {42, 43, 44, 41};
> > Line Loop(48) = {22, 23, 24, 21};
> > Plane Surface(47) = {46, 47, 48};
> > Physical Surface(98) = {26};
> > Physical Surface(99) = {46};
> > Physical Surface(100) = {47};
> >
> > surfaceVector[] = Extrude {0, 0, c} {
> >      Surface{6};
> >     Layers{15};
> >      Recombine;
> >     };
> >
> > // volume and top mesh
> > Physical Volume("internal") = surfaceVector[1];
> > Physical Surface(201) = {16};
> > Physical Surface(202) = {36};
> > Line Loop(54) = {49,51,52,47};
> > Plane Surface(203) ={54, 15, 35};
> > Physical Surface(203)={203};
> >
> >
> > In Gmsh, to see that the bottom surface mesh is correct, go to
> Visibility and select Surfaces 98, 99 and 100. To see that the top surface
> mesh is wrong, select the surfaces 201, 202 and 203.
> >
> > Thanks!
> > _______________________________________________
> > gmsh mailing list
> > gmsh at onelab.info
> > http://onelab.info/mailman/listinfo/gmsh
>
> —
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
>
>
>
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