[Gmsh] Mesh size definition referring to surface or volume numbers.

[Mark Starnes]

Hi Geordie,  thanks for the rapid reply.

Your example helped a great deal.  Thanks!
I went on with it, attempting to define the
field for more than one surface, using MathEval
to set the mesh size for an initial field, then 
defined a new second field for each surface using 
Restrict (following your example).

Can you tell me how to combine these field
definitions, please?  I tried Min, Max, MathEval
and MinAniso types to define my last field
(referenced as the background field) but the
element sizes in different regions all appear the
same.

I have attached my efforts (for what they are worth).  

Thanks again for the help.

Best regards,

Mark.



On Wed, May 25, 2011 at 02:45:38AM +0100, Geordie McBain wrote:
> 2011/5/25 Mark Starnes <mark.starnes at fttech.co.uk>:
> > Hi everyone,
> >
> > Can you please tell me if it is possible to
> > specify the size of elements in a region based on, for example, the
> > region number and a transition distance? ?I usually define my
> > element sizes during Point definitions and on
> > occasion using Fields, but I have some geometries
> > for which I would like to set the target element size by
> > Surface number or Volume number. ?The reason for
> > this is that I'm coupling regions with requiring
> > dissimilar mesh densities; these regions are
> > complex enough for me to feel apprehension at the
> > thought of attempting to define geometric objects
> > inside the regions to define mesh fields.
> >
> > Is this approach possible?
> 
> Yes, use Restrict
> <http://geuz.org/gmsh/doc/texinfo/gmsh.html#index-Restrict-309>.  For
> example, to refine just Plane Surface (9), use:
> 
>   Field[1] = MathEval;
>   Field[1].F = "0.1";
> 
>   Field[2] = Restrict;
>   Field[2].IField = 1;
>   Field[2].FacesList = {9};
> 
>   Background Field = 2;
> 
> I attach a complete example.




-- 
Dr. Mark Starnes
Senior Physicist
FT Technologies
Church Lane
Teddington
TW11 8PA

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-------------- next part --------------
Point (1) = {0, 0, 0};		// -*- c++ -*-
Point (2) = {1, 0, 0};
Point (3) = {2, 0, 0};
Point (5) = {1, 1, 0};
Point (9) = {1, -1, 0};

Line(1) = {1, 2};
Line(2) = {2, 3};
Line(3) = {3, 5};
Line(5) = {5, 1};
Line(7) = {5, 2};


Line Loop(8) = {1, -7, 5};
Plane Surface (9) = {8};
Line Loop(10) = {7, 2, 3};
Plane Surface (11) = {10};

Line(12) = {1, 9};
Line(13) = {9, 2};
Line(14) = {9, 3};

Line Loop(15) = {1, -13, -12};
Plane Surface(16) = {15};
Line Loop(17) = {2, -14, 13};
Plane Surface(18) = {17}; 

Field[1] = MathEval;
Field[1].F = "0.01";  // Sets the element size in the left region (9)

Field[2] = MathEval;
Field[2].F = "0.02";  // Sets the element size in the left region (9)
 
Field[3] = MathEval;
Field[3].F = "0.04";  // Sets the element size in the left region (9)
 
Field[4] = Restrict;
Field[4].IField = 1;        
Field[4].FacesList = {9};

Field[5] = Restrict;
Field[5].IField = 2;
Field[5].FacesList = {11};

Field[6] = Restrict;
Field[6].IField = 3;
Field[6].FacesList = {16};

 
// Field[7] = Min;  // all elements are tiny.
// Field[7] = Max;  // all elements are large.
// Field[7].FieldsList = {1,2,3,4,5};

// Field[7] = MathEval;
// Field[7].F = "F4 + F5 + F6";  // All elements are the same size.

// Field[7] = MinAniso;
// Field[7].FieldsList = {4,5,6}; // All elements are large.

Background Field = 7;