以布拉格光纖光柵感測器量測與分析固液耦合結構物的動態特性及暫態波傳問題

Application of the Fiber Bragg Grating Sensor on Measuring and Analyzing Dynamic Characteristics and Transient Wave Propagation of Solid-liquid Structures

李冠德(Kuan-Te Lee)

指導教授 ： 馬劍清

國立臺灣大學/工學院/機械工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601366

摘要

光纖感測器擁有優良的機械性質以及線狀幾何特質、不受電磁波干擾以及高靈敏度等優點，近年來特別以布拉格光纖光柵（Fiber Bragg Grating, FBG）作為感測器的相關研究發展十分迅速，可以搭配波長解調器進行靜態的監測、利用能量調變型光纖光柵作動態的量測，上述兩種方法也可以使用分波多工器來達到同時多點的量測。數位影像相關法（Digital Image Correlation, DIC）可進行非接觸式全域的位移及應變的量測。聚偏二氟乙烯壓電薄膜（PVDF）具有優異的壓電特性，具有輕薄如紙、柔韌可撓、可自行剪裁適合尺寸等特性，因而廣泛應用於感測器或傳感器等研究。以上量測技術本實驗室已投入相當多的研究，且擁有十分成熟的技術，將利用以上感測器應用於本文的研究中。
本文主要利用布拉格光纖光柵感測器徑細質輕、具可撓性、能在水中甚至腐蝕性液體中進行量測等特性，搭配本實驗室自行開發的能量調變法，利用圓柱及懸臂板系統，說明FBG有能力在空氣中以及水中進行單方向的應變量測能力。同時使用光纖位移計（FS）進行位移、速度、加速度等分析，增加實驗的可信度，並透過模態的分析探討頻率分布是否合理。也搭配DIC進行懸臂薄板側面隨時間的位移量測，顯示出每個時間點的懸臂薄板形狀，再使用濾波的方式，用實驗的方法呈現出前三共振頻對應的模態形狀。此外搭配波長解調器（I-MON）探討懸臂板系統於各種固液耦合條件下的頻率變化趨勢。最後藉著FS優異的頻率解析能力，配合數值模擬數據建立的資料庫，在懸臂樑系統上預測缺口的長度及位置。

關鍵字

布拉格光纖光柵 ； 數位影像相關法 ； 聚偏二氟乙烯壓電薄膜 ； 能量調變法 ； 位移 ； 應變 ； 缺口效應 ； 頻率飄移

並列摘要

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.

並列關鍵字

Fiber Bragg Grating ； Digital Image Correlation ； PVDF ； power modulated method ； displacement ； strain ； crack effect ； frequency shifting

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