[Gmsh] Applying Boundary conditions using gmsh

[Vaibhav Deshpande]

Hi,

I am Vaibhav Deshpande a Graduate student at University of Wisconsin
Madison, In one of my projects I have implemented Quad4 plane stress element
and I am using gmsh as my mesher, the geometry I am using is of a cantilever
beam made of lines

1-2
2-3
3-4
4-1

where 1 2 3 4 are the coordinates of geometrical points
x y coordinates for nodes are
1, 0 0
2, 10 0
3, 10 1
4,0 1

what I want to do now is apply a pressure on line that
joins geometrical points 3 and 4 I was able to find the mesh lines
corresponding to geometrical line 3-4 using the code given below. I need to
find Jacobian of all the elements whose sides have an applied pressure. The
Jacobian is a function of coordinates of that element.

Simply put given a side I want to know which elements are made up of that
side. I can imagine that gmsh has that piece of information in some or the
other way, but I was not able to get that information as an output.

I am using following geometry file.

/*********************************************************************
 *
 *  Gmsh cantilever beam
 *
 *********************************************************************/

lc = 0.5;

Point(1) = {0, 0, 0, lc};
Point(2) = {10, 0,  0, lc} ;
Point(3) = {10, 1, 0, lc} ;
Point(4) = {0,  1, 0, lc} ;

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

Line Loop(5) = {4,1,-2,3} ;

Plane Surface(6) = {5} ;

MyLineThree = 3;
Physical Line (MyLineThree) = {3} ;

MyLineFour = 4;
Physical Line (MyLineFour) = {4} ;

Physical Surface("Mesh") = {6} ;

the boundary conditions I want to apply are on line 4 is Dirichlet boundary
condition, which I was able to figure out,

the second boundary condition is on line 3 I want to apply a pressure on all
the elements on the top that share an edge with line 3 how should I access
this information?

Please let me know how I can go about it. Thanks a lot.

-- 
Regards,
Vaibhav Deshpande
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