Nonlinear feedback auxiliary signals for system interrogation and damage detection

摘要

Recently, a sensitivity-enhancement technique for system interrogation using linearncontrollers and eigenstructure assignment has been extended from linear to nonlinearnsystems. Nonlinearities have been accounted for by forming (higher dimensional)naugmented systems that are designed for each trajectory of the nonlinear system, and arencharacterized by a specific forcing which ensures that the augmented systems follow thatntrajectory (when projected onto the original lower dimensional space). The use of systemnaugmentation has several benefits beyond its ability to handle nonlinearities. Fornexample, sensitivity can be increased compared with existing linear techniques throughnnonlinear feedback auxiliary signals (NFASs) because the constraint that the system isnstable during its interrogation has to be applied only to the linearized closed-loop system,nwhile the augmented linear system does not have that constraint. In this work, NFASsnare designed for interrogating linear systems. System augmentation is used in a linearnsystem because a nonlinear controller is employed to enhance sensitivity. In addition tonthe increased sensitivity, fewer controller actuator points and sensors are requiredncompared with existing linear techniques due to the efficient use of added (augmented)nequations. To demonstrate the approach, damage detection is considered as annapplication. Numerical simulations for linear mass–spring and mass–spring–dampernsystems are used to validate the approach and discuss the effects of noise.