[Getfem-users] Computation of forces for prescribed displacements

[Igor Peterlik]

Hello,

I have a question about the boundary conditions.
I am using your test demo nonlinear_elastostatic.cc . Let's suppose
I neither consider the gravitation forces nor the torsion, but
I just prescribe some extension (ie. I displace the top face of the bar
using the Dirichlet boundary conditions).
What I want is to compute the deformation of the bar (that is OK)
but moreover, I want to calculate the force vector which is acting
in the top face which is displaced. I use the AUGMENTED_CONSTRAINTS
for the Dirichlet condition and so
for each prescribed displacement in the nodes of the top face I get
a coefficient in the solution vector. How can I use them in GetFem
to compute the overall force vector (f_x, f_y, f_z)?

I tried simpler version of the deformation -- I just prescribed the 
displacement one
node of the mesh (in x,y,z). Then (using again the AUGMENTED_CONSTRAINTS)
I got three numbers in the tail of the solution vector and I considered
them being the forces f_x, f_y and f_z acting in that displaced point of the 
mesh.
Is this correct?


        Thank you in advance


                                Igor

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