[Gmsh] length refinement using the box field

[Mike B.]

Hi Shawn,

Try adding all these options at the begining of your script:
Mesh.CharacteristicLengthFromPoints = 0;
Mesh.CharacteristicLengthExtendFromBoundary = 1;
Mesh.CharacteristicLengthFromCurvature = 0;
Mesh.CharacteristicLengthMin = lc/20;
Mesh.CharacteristicLengthMax = lc;

Let me know if this works for you.

Cheers.
Mike.

--- On Wed, 7/15/09, Shawn Fostner <sfostner at physics.mcgill.ca> wrote:

From: Shawn Fostner <sfostner at physics.mcgill.ca>
Subject: [Gmsh] length refinement using the box field
To: gmsh at geuz.org
Date: Wednesday, July 15, 2009, 5:27 AM

Hi,

I've been just starting to use the the software to the point where I think I understand what I'm doing, to a point, but using fields to locally refine the mesh is stumping me. I have a volume defined with two holes in it, nearby to eachother (ie within 10's of units inside of a cube 1000 units across), and other other volume nearby. One element being a spherical tip on something, the other a rectangular edge. The problem is getting sufficient refinement between the two, as locally my physical variables, electric fields in this case, vary rapidly there.

I've tried using a box field as the simplest way I can see to refine the mesh in that region between the two, but haven't had much luck. Near as I can tell its not doing anything at all as I vary the VIn field. I've tried playing with the characteristic length, the internal size, the max element size in the mesh options etc. I should note that the box is actually overlapping two volumes, as the other volume is spatially close by as well. 
I have looked at some of the suggestions, and toyed with the other methods for changing characteristic lengths, but without much success. Either I can do it globally (lc in each point definition and/or max element size), or not at all. And computationally, globally gets simply too slow, or crashes, before I reach the point where the mesh is sufficiently refined in the critical region.

last few lines of the geo file:

Field[1] = Box;
Field[1].VIn = lc/20;
Field[1].VOut = lc;
Field[1].XMax = -50;
Field[1].XMin = 50;
Field[1].YMax = -100;
Field[1].YMin = 50;
Field[1].ZMax = 275;
Field[1].ZMin = 350;

Background Field = 1;

Thoughts? Something blindingly obvious I'm missing?

Thanks
Shawn


-- 
Shawn Fostner
PhD Candidate, Physics Department, McGill University
3600 University, Montreal QC, H3A 2T8
phone: (514) 398-6749


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