[Gmsh] Question about mesh refinement with stating of characteristic lengths

[Moritz Nadler]

Hallo ,


while creating my second mesh with gmesh I ran a problem:

I have created a mesh with
gmsh -rand 1.e-8 lightmillPeriodic.geo -2
and this .geo file:

//begin file
highPr = 0.000015;
midPr = 0.0002;
lowPr = 0.0006;
vLowPr = 0.001;

Point(1) = {0,0,0,highPr};
Point(2) = {0.25E-2,0,0,midPr};
Point(3) = {0.5E-2,0,0,highPr};
Point(4) = {0.5E-2,0.025E-2,0,highPr};
Point(5) = {0.75E-2,0.025E-2,0,midPr};
Point(6) = {2.25E-2,0.025E-2,0,midPr};
Point(7) = {2.5E-2,0.025E-2,0,highPr};
Point(8) = {2.5E-2,0,0,highPr};
Point(9) = {2.75E-2,0,0,midPr};
Point(10) = {4E-2,0,0,lowPr};
Point(11) = {9.5E-2,0,0,vLowPr};
Point(13) = {0,9.525E-2,0,vLowPr};
Point(14) = {0,4.025E-2,0,lowPr};
Point(15) = {0,2.775E-2,0,midPr};
Point(16) = {0,2.525E-2,0,highPr};
Point(17) = {0,2.275E-2,0,midPr};
Point(18) = {0,0.775E-2,0,midPr};
Point(19) = {0,0.525E-2,0,highPr};
Point(20) = {0,0.275E-2,0,midPr};
Point(21) = {0,0.025E-2,0,highPr};

// dummy point to lower the mesh density in this area (does not work)
Point(22) = {0.25E-2,0.275E-2,0,midPr};

Line(1) = {1,2};
Line(2) = {2,3};
Line(3) = {3,4};
Line(4) = {4,5};
Line(5) = {5,6};
Line(6) = {6,7};
Line(7) = {7,8};
Line(8) = {8,9};
Line(9) = {9,10};
Line(10) = {10,11};
//Line(11) = {11,12};
//Line(12) = {12,13};
Circle(11) = {11,1,13};
Line(13) = {13,14};
Line(14) = {14,15};
Line(15) = {15,16};
Line(16) = {16,17};
Line(17) = {17,18};
Line(18) = {18,19};
Line(19) = {19,20};
Line(20) = {20,21};
Line(21) = {21,1};

Line Loop(22) = {1,2,3,4,5,6,7,8,9,10,11,13,14,15,16,17,18,19,20,21};
Plane Surface(23) = {22};
// end file

But as it is stated in the gmsh manual
"The size of the mesh elements will
then be computed by linearly interpolating these characteristic lengths on the 
initial
mesh (see Section 1.2 [Mesh], page 3). This might sometimes lead to over-refinement
in some areas"

it did lead to some over-refinement in areas where I do not need a high mesh density

so I wanted to:
"so that you may have to add “dummy” geometrical entities in the model
in order to get the desired element sizes."

so I added a first dummy point (the point with the comment in my .geo file) with 
a lower ch. length to lower the mesh density in that area but the point is 
totally ignored by the meshing routine; it is not even used as a node.


I hope I could explain what I want to do my question then is of course:
what to do to do it right?


Thanks very much and

kind regards


Moritz Nadler