| Interferometric fiber optic sensors, using Mach-Zehnder interferometers, have been shown to produce accurate strain measurements (Wanser and Wang, 1989). In an effort to advance the state of the art in smart structures technology, a modified all-fiber Mach-Zehnder interferometer employing single-mode optical fibers and an active homodyne phase-demodulation technique is used to provide structurally integrated optical sensor outputs for vibration control of flexible structures. Sensors of this type, called distributed-effect sensors, respond to changes along their gauge length and provide time varying scalar quantities corresponding to the distributed quantities being measured. The distributed-effect sensor sensitivity (or sensor weighting function) as well as its output model are developed and integrated into the dynamic models of two composite flexible structures to illustrate through simulation the feasibility of using optical sensors in the active control of flexible structures. For a selected optical fiber sensor, the experimental sensitivity is determined to be about 13% less than the analytically developed one. In addition, the experimental modal frequencies were found to deviate from those of the analytical and finite element models by only 3% for the first three bending modes of a beam structure; whereas for the lattice structure, the finite element and experimental modal frequencies were determined to agree within 35% for the first six modes. Furthermore, the effects of the weighting function selection, sensor placement, and sensor type on the performance of a control system as well as sensor output are investigated. Simulation results indicated that distributed-effect sensors provide an improved performance over discrete sensors, in particular for complex structures. In addition, effects of introducing observation and control spillovers on the system performance were examined. Results obtained through simulations, for the lattice structure, reveals that distributed-effect sensors are less sensitive to spillovers and provide a better transient and steady state response when compared to discrete sensors. |
