[Getfem-users] Rigid body elements

[Konstantinos Poulios]

Hi,

I am trying to model a torsion moment applied onto a shaft. A common
practice in a commercial FE- Solver would be to define a single node
with 6 dofs lying on the axis of the shaft. Then connect this node via
rigid body elements with the nodes lying on the cross-section of the
shaft where the torsion moment is to be introduced. Finally, constrain
5 dofs of the previously defined single node and apply the torsion
moment as a neumann condition on its 6th rotational dof.

In order to transfer this technique to getfem I thought to define a
fixed size variable of size 6 to represent the single node and add
constraints between this variable and the shafts dofs lying on the
considered cross-section to represent the so called "rigid body
elements". Though, I realized that the constraint brick can be defined
only on a single variable, so it is not possible to use it in order to
interconnect dofs from two different variables.

I wonder if it is a good idea to extend the constraint brick in a way
that it can accept two variables or if there is a simpler technique to
solve my problem. Does it make sense to introduce some kind of "rigid
body elements" into getfem based on such an extended two variables
constraint brick?

Kostas