[Gmsh] Questions on the background mesh/data

[dolfyn]

Dear all,

Intrigued by the possibility to use STL files I decided to try one. 
Found a STL file on the internet of a man. First runs in Gmsh did 
not succeed; the STL file needs to be closed and not too wild (no 
intersecting triangles). 

Using the default meshing algorithm works; Mesh.Algorithm3D = 4 does 
not. Results, see figure, look nice.

Next step is to go for a 'poor mans mesh refinement' i.e. not 
automatic but stopping the simulation run, remesh based on the 
results so far, interpolate old results on the new mesh and start a 
new analysis. The method of exporting a field out of dolfyn to Gmsh 
is in place (the interpolation subroutines have to be written).

Some questions:
1) Obviously the first mesh is driven by the STL surface details 
(and if I may say so, very well). Is there any way to control it's 
behavior/characteristic length attractor or distance threshold?
2) What is the characteristic length? A sphere within the 
tetrahedral cell? Does not seem to be the case, nor is an edge 
length. What is it? Volume?
3) The background field is it cell/zone based or on the 
vertices/nodes? 
4) Can I switch off Gmsh random meshing? (useful when debugging)

Not related... but... is it possible to 'push' away the layer at the 
surface and as a result we'll have one or more prism layers next to 
the surface?

Regards and thanks in advance!
Henk

=== man.geo ===

//Mesh.Algorithm3D   = 4 ;
Geometry.Tolerance = 1.e-6;
MeshSize =  2.  ;
StdSize  = 10.  ;

Merge "man_model.stl" ;

// a small 'tunnel':
Point(1) = { 1.5 * StdSize,-13.0, 1 * StdSize, MeshSize};
Point(2) = {-1.5 * StdSize,-13.0, 1 * StdSize, MeshSize};
Point(3) = {-1.5 * StdSize,-13.0,-2 * StdSize, MeshSize};
Point(4) = { 1.5 * StdSize,-13.0,-2 * StdSize, MeshSize};

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

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

Extrude{0, 3.0 * StdSize, 0 }{ Surface{2}; }
//Delete{ Volume{1}; }

Surface Loop(1) = {1};
Surface Loop(2) = { 2, 13, 17, 21, 25, 26};

//Volume(1) = {1}; // interior STL model
Volume(2) = {2,1};

Physical Volume("Fluid")  = {2};

Physical Surface("Man  ") = {1};
Physical Surface("Floor") = {2};
Physical Surface("Inlet") = {13};
Physical Surface("Outlet") = {21};
Physical Surface("Walls") = {17, 25, 26};

=== mand.din ===

title Test Gmsh man model
steps 1000 1.e-3

opendx off
#use gmsh
use vtk

density,1.0
vislam 18.6e-6
pref,85562

relax 0.4 0.1 0.4 0.8
#thermal on
init,field,0.0 0.0 -0.1,,1.e-4,1e-4

scheme UVW  GAMMA
scheme T    LUX 0.8

slope UVW  vnf
slope P    vnf
slope KEPS vnf
slope T    vnf

post p    vert

boundary,man
wall
noslip
0.0 0.0 0.0
fixed
273 + 38 0.0

boundary,inlet
inlet
0.0 0.0 -1.0
1.0
293
inle
0.25 0.01

boundary,outlet
outlet
1.0

boundary,floor
symp

boundary,walls
symp
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