# [Gmsh] Dilate after Extrusion for transfinite extruded meshes

Pfender, Ferdinand ferdinand.pfender at tu-berlin.de
Wed Jan 20 15:38:04 CET 2016

```Hi everyone!

I want to create a structured channel-mesh, containing some stuff, with a reduction at the end.

For this, i take the bottom lines at the position where the reduction should start, extrude them and dilate them to get the  reduction.
The Problem is, the Dilation has only correct effect on the existing geometry. The Meshlines and Nodes are still on the same position, except the ones on the extruded Line.

I attached two pictures which show the problem very well.

It would be nice if someone could help and if there is a solution.

code snippet:

lc = 0.3;

Point(1) = {0.0,0.0,0.0,lc};
Point(2) = {0,1,0.0,lc};
Point(3) = {0,1,1.0,lc};
Point(4) = {0,0,1.0,lc};

Line(1) = {4,3}; Transfinite Line{1} = 10;
Line(2) = {3,2}; Transfinite Line{2} = 10;
Line(3) = {2,1}; Transfinite Line{3} = 10;
Line(4) = {1,4}; Transfinite Line{4} = 10;

Line Loop(5) = {2,3,4,1};

Ruled Surface(6) = {5};

Transfinite Surface{6} = {1,2,3,4};

Recombine Surface {6};

extruded[] = Extrude {2,0,0} {
Surface{6}; Layers{10}; Recombine;
};

temp[] = Boundary{Surface{extruded[0]};};

line_for_reduction=temp[1];

Physical Line ("test") = temp[1];

reduction_without_dilate[] = Extrude {0.5,0,0} {
Line{line_for_reduction}; Layers{10}; Recombine;
};

Dilate {{2.375,0.5,0}, 0.75} {
Line{reduction_without_dilate[0]};
}

Show "*";

Thank you very much!
Ferdinand Pfender
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```