Rigid Link

A rigid link imposes the same velocity on all secondary nodes in one or more directions. The directions are defined to a skew or global frame. Figure 1 displays a rigid link.
The velocity of the group of nodes rigidly linked together is computed using momentum conservation (Section Definition, Equation 1). However, no global moment equilibrium is respected.(1)
Vi=i=iNmivii=iNmi
Angular velocity for the ith DOF with respect to the global or a skew reference frame is:(2)
ωi=(j=1nIjiωji)(j=1NIji)

For non-coincident nodes, no rigid body motion is possible.

A rigid link is equivalent to an infinitely stiff spring TYPE8.