[Gmsh] Attractor around a point in 3D

[Christophe Geuzaine]

Srinath Madhavan wrote:
> Hi all,
> 
> I have a simple cube and a point at the center. Using attractors, I'm trying to refine the mesh around the point and make it coarse as we move away from the point. The code I use is pasted below:
> 
> ************CODE BEGINS*************
> 
> lc = 0.15;
> Point(1) = {-0.5, -0.5, -0.5, lc};
> Point(2) = {0.5, -0.5, -0.5, lc};
> Point(3) = {0.0, 0.0, 0.0, lc};
> Line(3) = {1, 2};
> 
> e1[] = Extrude{0, 1, 0}{Line{3};};
> e2[] = Extrude{0, 0, 1}{Surface{e1[1]};};
> 
> // Attractor field on point 3. This field returns the
> // distance to point 3.
> Field[1] = Attractor;
> Field[1].NodesList = {3};
> 
> // Threshold field using the return value of the attractor field 1 in
> // order to define a simple change in element size around the
> // attractors (i.e., around point 3)
> //
> // LcMax -                         /------------------
> //                               /
> //                             /
> //                           /
> // LcMin -o----------------/
> //        |                |       |
> //     Attractor       DistMin   DistMax
> Field[2] = Threshold;
> Field[2].IField = 1;
> Field[2].LcMin = lc / 30;
> Field[2].LcMax = lc;
> Field[2].DistMin = 0.05;
> Field[2].DistMax = 0.5;
> 
> // Use minimum of all the fields as the background field
> Field[3] = Min;
> Field[3].FieldsList = {2};
> Background Field = 3;
> 
> // Don't extend the elements sizes from the boundary inside the domain
> Mesh.CharacteristicLengthExtendFromBoundary = 0;
> 
> Physical Volume("domain") = {e2[1]};
> Physical Surface("wall") = {29,28,24,20,16,7};
> 
> ************CODE ENDS*************
> 
> The mesh generation works but I don't see any refinement around point 3. If however, I change the line:
> 
> Field[1].NodesList = {3}; TO Field[1].NodesList = {1};
> 
> Then I see refinement around point 1. This works for point 2 as well.
> 
> Can someone point out what I'm doing wrong here?


Works OK over here. Make sure you don't use the "Netgen" 3D algorithm: 
it does not support Fields (cf. the documentation).



> 
> Thanks & Best Regards,
> Srinath Madhavan
> PhD Student
> University of Alberta
> 
> Free as in Freedom. May the source be with you!
> 
> 
>       
> 
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> 
> 


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine