Orienting body coordinate frames using Karhunen–Loève expansion for more effective structural simplification

As part of an effort to create an automated modular modeling environment, previous work by the authors developed a junction-inactivity-based structural simplification technique that is particularly suitable for bond-graph models. The technique is highly sensitive to the orientation of the body coordinate frames in multibody systems: improper alignment of body coordinate frames may prohibit a significant simplification. This paper demonstrates how the Karhunen–Loève expansion can be used to automatically detect the existence of and to find the transformation into body coordinate frames that render the bond graph of a multibody system more conducive to simplification. The proposed technique is demonstrated using the simple example of a 3D pendulum constrained to move in a plane, but is applicable to arbitrarily complex multibody dynamics problems. The conclusion is that the Karhunen–Loève expansion successfully complements the junction-inactivity-based structural simplification technique when multibody dynamics are involved in the system, and thus significantly contributes to the development of an automated modular modeling environment.