On Mon, Dec 6, 2010 at 5:07 AM, robert <[email protected]> wrote:
> Hi,
>
> How can I create a mesh which has something like a whole in the middle?
> I need to have something which works in runtime because during my model
> (based on diffusion equation) chemical reactions and phase transitions
> occur.
You can use the Triangle mesh generator from within libmesh for this
purpose. I will try to paste an example code here, let me know if you
would like to receive it as a separate attachment...
--
John
#include "libmesh.h"
#include "mesh_triangle_support.h"
#include "mesh.h"
#include "postscript_io.h"
int main (int argc, char** argv)
{
// Use typedefs for slightly less typing.
typedef TriangleInterface::Hole Hole;
typedef TriangleInterface::PolygonHole PolygonHole;
typedef TriangleInterface::ArbitraryHole ArbitraryHole;
LibMeshInit init(argc, argv);
{
// Flag to turn on/off holes in the mesh
const bool with_hole=true;
// Libmesh mesh that will eventually be created.
Mesh mesh(2);
// The points which make up the L-shape:
mesh.add_point(Point( 0. , 0.));
mesh.add_point(Point( 0. , -1.));
mesh.add_point(Point(-1. , -1.));
mesh.add_point(Point(-1. , 1.));
mesh.add_point(Point( 1. , 1.));
mesh.add_point(Point( 1. , 0.));
// Declare the TriangleInterface, to be used later
TriangleInterface t(mesh);
// Customize the variables for the triangulation
t.desired_area() = .01;
t.triangulation_type() = TriangleInterface::PSLG;
// Define holes
PolygonHole hole_1(Point(-0.5, 0.5), // center
0.25, // radius
50); // n. points
PolygonHole hole_2(Point(0.5, 0.5), // center
0.1, // radius
3); // n. points
// The third hole is an ellipse
Point ellipse_center(-0.5, -0.5);
const unsigned int n_ellipse_points=100;
std::vector<Point> ellipse_points(n_ellipse_points);
const Real
dtheta = 2*libMesh::pi / static_cast<Real>(n_ellipse_points),
a = .1,
b = .2;
for (unsigned int i=0; i<n_ellipse_points; ++i)
{
ellipse_points[i]= Point(ellipse_center(0)+a*cos(i*dtheta),
ellipse_center(1)+b*sin(i*dtheta));
}
ArbitraryHole hole_3(ellipse_center, ellipse_points);
// Create the vector of Hole*
std::vector<Hole*> holes;
holes.push_back(&hole_1);
holes.push_back(&hole_2);
holes.push_back(&hole_3);
if (with_hole)
{
// Attach the list of holes to the triangulator object
t.attach_hole_list(&holes);
}
else
{
// Add extra points (for more randomness)
t.insert_extra_points() = true;
}
// Triangulate!
t.triangulate();
// Print result as GMV
if (with_hole)
{
mesh.write("delaunay_l_shaped_hole.gmv");
//PostscriptIO(mesh).write("delaunay_l_shaped_hole.ps");
PostscriptIO pio(mesh);
//pio.shade_value=0.75;
pio.write("delaunay_l_shaped_hole.ps");
}
else
{
mesh.write("delaunay_l_shaped.gmv");
//PostscriptIO(mesh).write("delaunay_l_shaped.ps");
PostscriptIO pio(mesh);
//pio.shade_value=0.75;
pio.write("delaunay_l_shaped.ps");
}
}
return 0;
}
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