Used For Vibration Measurements Of The Thin Structure Of The Research Of Distributed Optical Fiber Curvature Modal Sensors

Thin structures have been applied widely in different areas of engineering such as airfoil and the planes of architecture. They are prone to elastic vibration when submit to external dynamic excitations or interference, which will not only lower the system stability, but also threaten the people's lives.. Generally, many acceleration sensors are put on the cover of the structure to measure the vibrations. But the means is limited and can't meet extreme sensitivities in air field. Since practical structure is a complicated multiple degree of freedom system ,it can be regarded as the stack of multiple vibration mode. Therefore it is possible to control every single vibration mode if the vibration information can be decoupled.Recently strain sensors have been used for dynamic control of elastic vibrations. But strain is difficult to measure in thin structures since thinner the structure, the less strain there is to measure for the same magnitude of deflection. In contrast, curvature measurement are more appropriate for thin structures for the reason that curvature remains constant irrespective of the structural thickness. Based on the above concepts, a new concept of modal curvature sensors with optical fiber is proposed to measure vibration mode .The thesis studied the distributed modal curvature sensors for vibration measurement of thin structures theoretically and experimentally.The proposed curvature sensor operates on the principle of intensity modulation. The losses introduced by bending and highlighted zone .namely it is machined by cutting into the core of fiber. So the notable signals are acquired which related indirectly with vibration mode. In this paper theoretical study has been done from geometric optics and wave optics.Performances experiment, parameter experimental optimization, static and dynamic experiment of measurement on vibration mode have be done.According the result of the above experiment, optimized parameter can be acquired and the measurement method on distributed vibration mode is verified to be feasible.Further more ,the mechanism of the new concept of modal curvature sensors and the effects of bending extent and parameters of the sensors have been simulated .studied and analyzed with ANSYS5.7...