[Gmsh] length refinement using the box field

[Shawn Fostner]

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