Modal filter based on-line monitoring of uncertain structural systems

Identification of a structural system can be performed in a number of ways. The modal filter method has been used to develop single degree-of-freedom transfer functions from multimodal data for various linear time-invariant structures and has also been used in the implementation of modal control strategies. It may be desirable to apply these methods to systems whose behavior changes over time. Such engineering structures are numerous; in the aerospace field, aircraft are a classic example, where structural system identification performed in flight may yield vastly different results from similar tests on the ground due to aerodynamic coupling and loading. Some civil engineering structures, e.g., suspension bridges, may display the same type of behavior, though generally to a lesser extent. On-line monitoring of these time-varying structures, with special regard to structural integrity, poses a difficult problem, especially since the number of sensors in on-line monitoring may be limited. Various aspects of this problem will be discussed, particularly from the standpoint of monitoring critical modes of the structure.