Localisation of damage in smart structures through sensitivity enhancing feedback control

The concept of sensitivity enhancing control (SEC) introduced previously by the authors exploits the relationship between feedback control gains and classic measures of root and system sensitivity in order to increase the magnitude of variation in modal characteristics when damage occurs. This paper further develops the SEC concept, focusing on the ability to locate damage in smart structures. Two distinct methods are considered for locating damage. Forward methods rely on a priori knowledge of how certain damage scenarios affect modal properties. Using this information, the correlation between measured modal frequency shifts and predicted modal frequency shifts for a given set of damage scenarios is used to identify damage location. Inverse, or model updating methods attempt to update mass and/or stiffness matrices of structural models based on measured modal frequencies and mode shapes. The resulting perturbation matrices indicate damage location. Here, both methods are evaluated through finite-element simulation of controlled structures with local stiffness damage, with the goal of determining whether inclusion of modal data from feedback controlled structures enhances the localisation process. Results show that application of both forward and inverse methods to measured closed-loop modal characteristics increases both the accuracy with which stiffness damage can be located and the ability to tolerate noise in measurement of modal properties used to locate damage.