Re: [Getfem-users] Computation of forces for prescribed displacements

[Yves Renard]

On Wednesday 17 October 2007 10:10, you wrote:
> 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?
>

Yes, the component of the multiplier corresponding to a certain node 
represents a so called "equivalent force" at this node. If you need the force 
density, you have to use the shape functions of the multiplier fem used. 

Yves.

-- 

  Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
  Pole de Mathematiques,                       fax : (33) 04.72.43.85.29
  Institut Camille Jordan - CNRS UMR 5208
  INSA de Lyon, Universite de Lyon
  20, rue Albert Einstein
  69621 Villeurbanne Cedex, FRANCE
  http://math.univ-lyon1.fr/~renard

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