Rigid links are used to model rigid elements of elastic structures (definition
of a rigid body in a structure). Displacements and rotations defined for a rigid
link can be limited to certain selected degrees of freedom.
You need at least two nodes to define a rigid link, one parent node and one
or more child nodes. A parent node passes its parameters down to child nodes
during simulation.
Releases of specified degrees of freedom can be applied to start or the end of
the beam with possible elasticity.