| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 104 === In recent years, the optical fiber sensors, especially Fiber Bragg Grating (FBG) sensors, have been developed very rapidly due to its excellent mechanical properties, electromagnetics immunity and high sensitivity. FBG can be used to monitor the static problems by using I-MON system. It also can be used to measure the transient response of mechanical structures by using power modulating method. Both of them can be used to measure mutiple points simultaneously with wavelength division multiplexer. Digital image correlation (DIC) is a full field and non-contact measurement technique and can be widely used to measure displacement and strain. PVDF has some excellent properties, such as flexibility, piezoelectricity and can be made for any size. It is widely used as a sensor or a transducer. All of them were developed in our laboratory and will be used in this thesis.
The main object of this research is to use the advantages of FBG to perform the measurement under water to show it has the ability to measure the transient response of cylinder and cantilever plate structure in both air and water. Not only use FS sensor to measure displacement, velocity, acceleration field to enhance the credibility of experiment, but also use DIC to measure the dynamic displacement along the length of the plate. The transient displacement obtained by DIC can be filtered to construct the mode shape of plate. On the other hand, the boundary condition of the plate in the water can be checked by frequency annlysis of I-MON system. The last part of this research is focused on the prediction of the length and location of the defect in a beam structure from measured frequencies.
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