[Gmsh] Extrusion produces an incorrect number of layers

[Felix Salazar]

I'm building a cylindrical geometry using extrusion, and managed to put a
Bump like layer distribution, using a modified version of an example given
by Christophe in the mailing list. (It's actually a double progression).
The script is not clean, and probably not very efficient, but it works. Or
at least, it seems to work.

Part of my geometry includes a simple extrusion of a circle 3 times, with
different length and layer distribution. The 1st and 3rd section should be
identical. However, Gmsh is giving at least an additional layer in the 3rd
section, with the normal in the opposite direction of the rest of extrusion.

Here's the simplified script reproducing the problem. I tested it in Gmsh
2.8, 2.6 and 2.5, with the same result.

//==== BEGIN OF .GEO
/*==============================*/
/*==== Geometric parameters ====*/
/*==============================*/
D1 = 1;
D2 = 1.00;
L  = D1;
BL = 0.5;
//==============================
factorRefinement = 1.0;
core = 4;
radial = Ceil((R1+R2/4)/(BL/core));
Rprog = 0.9;
lc = R1*(Pi/2)/core;
z1 = Ceil(factorRefinement*(L)/lc);
z2 = Ceil(factorRefinement*(L/2)/lc);
Zbump = 1.35;
Geometry.ExtrudeReturnLateralEntities = 0;
//==============================
// LIST OF POINTS
Point(1) = {0,     0, 0};
Point(2) = {0,    R1, 0};
Point(3) = {0, BL*R1, 0};

rot1[] = Rotate { {0,0,1}, {0,0,0}, Pi/2} {
   Duplicata{Point{2,3};}
};
rot2[] = Rotate { {0,0,1}, {0,0,0}, Pi/2} {
   Duplicata{Point{rot1[0],rot1[1]};}
};
rot3[] = Rotate { {0,0,1}, {0,0,0}, Pi/2} {
   Duplicata{Point{rot2[0],rot2[1]};}
};

Circle(1) = {2, 1, rot1[0]};
Circle(2) = {rot1[0],1,rot2[0]};
Circle(3) = {rot2[0],1,rot3[0]};
Circle(4) = {rot3[0],1,2};
Line(5)   = {3, rot1[1]};
Line(6)   = {rot1[1],rot2[1]};
Line(7)   = {rot2[1],rot3[1]};
Line(8)   = {rot3[1],3};
Transfinite Line {1,2,3,4,5,6,7,8} = Ceil(factorRefinement*core+1);
Line(9)   = {3,2};
Line(10)  = {rot1[1],rot1[0]};
Line(11)  = {rot2[1],rot2[0]};
Line(12)  = {rot3[1],rot3[0]};
Transfinite Line {9,10,11,12} = Ceil(factorRefinement*radial+1) Using
Progression Rprog;

Line Loop(5) = {5,6,7,8};
Plane Surface(5) = {-5};
Line Loop(1) = {1,-10,-5,9};
Plane Surface(1) = {-1};
Line Loop(2) = {2,-11,-6,10};
Plane Surface(2) = {-2};
Line Loop(3) = {3,-12,-7,11};
Plane Surface(3) = {-3};
Line Loop(4) = {4,-9,-8,12};
Plane Surface(4) = {-4};
Transfinite Surface {5,1,2,3,4};

//======================
Function BumpExtrude
  n0 = Ceil(n/2);
  nN = n - n0;
  a0= (n0/n)*(r - 1) / ((r^n0) - 1);
  aN= (nN/n)*((1/r) - 1) / (((1/r)^nN) - 1);

  one[0] = 1;
  layer[0] = a0;
  Printf("%g   %g",0,layer[0]);
  For i In {1:n-1}
    one[i] = 1;
    layer[i] = layer[i-1] + a0 * r^i;
    If(i>=n0)
      layer[i] = layer[i-1] + aN * (1/r)^(i-n0);
    EndIf
    Printf("%g   %g",i,layer[i]);
  EndFor
Return
//======================
n =  3*(z2+1) - 1; // number of intervals
r = Zbump; // Bump progression
Call BumpExtrude;
Extrude {0,0,-L/2} {
  Surface{1,2,3,4,5}; Layers{one[], layer[]}; Recombine;
}
//======================
n =  3*(z1+1) - 1; // number of intervals
r = Zbump; // Bump progression
Call BumpExtrude;
Extrude {0,0,-L} {
  Surface{-34,-56,-78,-100,-122}; Layers{one[], layer[]}; Recombine;
}
//======================
n =  3*(z2+1) - 1; // number of intervals
r = Zbump; // Bump progression
Call BumpExtrude;
Extrude {0,0,-L/2} {
  Surface{-144,-166,-188,-210,-232}; Layers{one[], layer[]}; Recombine;
}
//=====OPTIONS=====
Geometry.AutoCoherence = 1;
Geometry.CopyMeshingMethod = 1;
Geometry.LightTwoSide = 0;
Geometry.Lines = 1;
Geometry.LineNumbers = 1;
Geometry.Points = 0;
Geometry.PointNumbers = 0;
Geometry.Surfaces = 1;
Geometry.SurfaceNumbers = 1;
Geometry.Volumes = 0;
Mesh.Algorithm = 6;
Mesh.Algorithm3D = 4;
Mesh.CharacteristicLengthExtendFromBoundary = 0;
Mesh.CharacteristicLengthFromCurvature = 0;
Mesh.CharacteristicLengthFromPoints = 0;
Mesh.ColorCarousel = 2;
Mesh.LabelType = 2;
Mesh.ElementOrder = 2;
Mesh.Light = 0;
Mesh.LightTwoSide = 0;
Mesh.Lines = 0;
Mesh.Optimize = 0;
Mesh.RandomFactor = 1e-6;
Mesh.ReverseAllNormals = 1;
Mesh.SaveElementTagType = 2;
Mesh.Format = 30;
Mesh.SecondOrderIncomplete = 0;
Mesh.SecondOrderLinear = 0;
Mesh.Smoothing = 0;
Mesh.SurfaceFaces = 1;
Mesh.VolumeEdges = 0;
Mesh.RecombineAll = 1;
Mesh.Color.Zero = {177,149,255};
Mesh.Color.One = {255,6,0};
Mesh.Color.Two = {0,255,71};
Mesh.Color.Three = {0,54,255};
Mesh.Color.Four = {255,155,0};
Mesh.Color.Six = {0,255,184};
Mesh.Color.Seven = {195,255,152};
Mesh.Color.Eight = {255,35,247};
//END OF .GEO

Note that the parameters for the first and 3rd extrusions are identical,
with the exception of the surface list.

I added a couple of lines, to print into console the position of the
layers. The 1st and 3rd layer, with the parameters of the example, have 8
layers according to the printed info, but the mesh on the screen shows
something different.

I tried tweaking some of the meshing options, without success. Displaying
the normals show that the extra layer is somewhat "inverted" if compared
with the others.

Is there anything wrong with my Mesh options? Or the script has an error
that I can't see. Any help is appreciated.

Thanks,

------------------------------------

* Félix Salazar**felix.salazar at polymtl.ca <felix.salazar at polymtl.ca>*
Étudiant au doctorat - PhD Student
*École Polytechnique de Montréal*
*     LADYF*
     Lab. de dynamique des fluides
(514) 340 4711 ext 2489
Local: C-318.21.3
------------------------------------
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.geuz.org/pipermail/gmsh/attachments/20131105/2564aeb9/attachment.html>