// Custom function to calculate drag coefficient.
double integrate_over_wall(MeshFunction* meshfn, int marker)
{
Quad2D* quad = &g_quad_2d_std;
meshfn->set_quad_2d(quad);
double integral = 0.0;
Element* e;
Mesh* mesh = meshfn->get_mesh();
for_all_active_elements(e, mesh)
{
for(int edge = 0; edge < e->nvert; edge++)
{
if ((e->en[edge]->bnd) && (e->en[edge]->marker == marker))
{
update_limit_table(e->get_mode());
RefMap* ru = meshfn->get_refmap();
meshfn->set_active_element(e);
int eo = quad->get_edge_points(edge);
meshfn->set_quad_order(eo, H2D_FN_VAL);
scalar *uval = meshfn->get_fn_values();
double3* pt = quad->get_points(eo);
double3* tan = ru->get_tangent(edge);
for (int i = 0; i < quad->get_num_points(eo); i++)
integral += pt[i][2] * uval[i] * tan[i][2];
}
}
}
return integral * 0.5;
}
//------------------------------------------------------------------------------
// Compute marked boundary length
//
double CalculateBoundaryLength(Mesh* mesh, int bdryMarker)
{
// Variables declaration.
Element* e;
double length = 0;
RefMap rm;
rm.set_quad_2d(&g_quad_2d_std);
Quad2D * quad = rm.get_quad_2d();
int points_location;
double3* points;
int np;
double3* tangents;
// Loop through all boundary faces of all active elements.
for_all_active_elements(e, mesh) {
for(int edge = 0; edge < e->nvert; ++edge) {
if ((e->en[edge]->bnd) && (e->en[edge]->marker == bdryMarker)) {
rm.set_active_element(e);
points_location = quad->get_edge_points(edge);
points = quad->get_points(points_location);
np = quad->get_num_points(points_location);
tangents = rm.get_tangent(edge, points_location);
for(int i = 0; i < np; i++) {
// Weights sum up to two on every edge, therefore the division by two must be present.
length += 0.5 * points[i][2] * tangents[i][2];
}
}
}
}
return length;
} // end of CalculateBoundaryLength()