[Gmsh] help refining a mesh around the boundary of a plane (3-D)

[Terrence Moran]

Hello all,

I am trying to refine a mesh to be very fine around a curve and very coarse
away from it. This works very well using one or two curves (photo 1) using
Distance and Threshold. When I try and do more curves (completing a
circuit)  the mesh becomes fine everywhere on the plane (Photo 2) ignoring
the mesh size at DistMax. I understand there are other functions such as
Box or cylinder but I need this to work for any geometry. My code is below,
It is a simple example of a box. The loop is to find the lines that make up
the surface on which I am trying to refine the boundary. Any help would be
greatly appreciated!

Thanks,
Terrence
[image: photo1.PNG]
[image: photo2.PNG]
//+
SetFactory("OpenCASCADE");
ShapeFromFile("box.iges")
//+
lns[];
h = 0;
For i In {1:newl-1}
  pnts[] = Boundary{Line{i};};
  Printf("line %g",i);
  Printf("point one = %g",pnts[0]);
  Printf("point two = %g",pnts[1]);
  coords1[] = Point{pnts[0]};
  coords2[] = Point{pnts[1]};
  If(coords1[2]==254 && coords2[2]==254)// 254=top surface z coord
    Printf("line %g is on boundary",i);
    lns[h] = i;
    h = h+1;
  EndIf
EndFor
Field[1] = Distance;
Field[1].EdgesList = {lns[]};
Field[1].NNodesByEdge = 100;
Field[2] = Threshold;
Field[2].IField = 1;
Field[2].LcMin = 0.5;
Field[2].LcMax = 100;
Field[2].DistMin = 1;
Field[2].DistMax = 50;
Background Field = 2;
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