Interaction in primary-secondary systems

Primary-secondary systems, consisting of a primary subsystem supporting a relatively light secondary subsystem, are characterized by special dynamic characteristics. One important characteristic is interaction, whichis mathematically manifested by coupling between the equations of motion ofthe two subsystems and results in a reduction in the secondary response. The dynamic analysis of PS systems is often performed using a decoupled system of equations which is simpler to analyze, but may give overly conservative results leading to unnecessarily costly designs. In this paper, interaction in PS systems is examined in detail, criteria for assessing the importance of interaction are developed, and the concepts are illustrated with examples of interacting systems.