【作者】 芦吉云；

【导师】 梁大开；

【作者基本信息】 南京航空航天大学 ， 测试计量技术及仪器， 2009， 博士

【摘要】 光纤Bragg光栅(FBG)传感器具有传、感一体的独特优点,可以在同一根光纤上布置许多传感点,构成分布式传感系统,适合于制作结构的健康监测网络,因此,光纤Bragg光栅在智能结构健康监测领域具有非常广阔的应用前景。本文对光纤Bragg光栅应用于智能结构的动态信号进行监测。研究了动态信号的采集方法、信号特征量提取及定位算法,构建了一个具有冲击载荷自诊断功能的光纤智能结构系统。同时,对光纤Bragg光栅传感器应用车架结构健康监测进行了初步研究。文中主要研究工作内容有以下几个方面:(1)对光纤Bragg光栅的光谱进行了仿真,研究了光栅长度与折射率调制周期改变情况下,FBG的反射、透射光谱。对光纤Bragg光栅的应变传感特性进行了实验研究,得到了光纤Bragg光栅中心波长的变化量与应变成线性关系的结果,所以可以通过监测光纤Bragg光栅中心波长的变化来监测结构的应变。(2)为对光纤Bragg光栅动态信号进行监测,提出了一种基于双长周期光栅的光纤Bragg光栅的高速解调系统。双长周期光栅是由两个中心波长一致的长周期光栅构成,利用长周期光栅的带阻滤波特性,获得光纤Bragg光栅反射光经双长周期光栅调制后的出射光,通过光电探测器监测光强的改变量来反推光纤Bragg光栅中心波长的变化。解调系统采用全光纤技术,结构紧凑、精度高,具有较好的线性输出。(3)对基于光纤Bragg光栅网络的振动、冲击监测方法进行了研究。多个光纤Bragg光栅传感器复用构成分布式光纤传感网络作为光纤智能结构的神经系统,通过对光纤Bragg光栅中心波长的分析,实现了该结构的振动、冲击响应监测。对不同冲击点,传感器监测的冲击响应信号进行了分析。(4)提出一种冲击载荷定位算法,对传感器采集的冲击响应信号进行特征提取,采用小波包分析方法提取冲击响应不同频段内的信号能量特征指标。将模态频率对应的能量值作为样本,采用支持向量回归机对有限样本数据建立回归模型,实现了复合材料试件的冲击载荷定位。(5)将光纤Bragg光栅应用于汽车车架结构健康监测领域,研究在不同工况下,车架受到的动态载荷情况。通过车架振动实验、整车瞬态冲击实验和路面实验对车架振动情况进行分析。更多还原

【Abstract】 Fiber Bragg grating (FBG) sensors have been expected to candidates for distributed sensoring system by arrangement many sensors in a single fiber because of their transmission and Sensing property. Besides these advantages, FBG sensors are Suitable for manufacturing network of structural health monitoring, FBG sensors have extensive potential applications in smart structure and materials health monitoring field. FBG sensors are applied for the dynamic signal monitoring of smart structure in the paper. In order to built a impact loading self-diagnosing system, Acquisition methods of dynamic signal, feature extraction and loading location algorithm are researched. Meanwhile, a preliminary study of vehicle frame health monitoring based on Fiber Bragg grating sensors is proposed in the paper.The main achievements are described as follows:(1) Spectrum numerical simulationof FBG is studied in the paper. In order to study sensing properties of FBG, reflectivity and transmission spectrum of FBG is analyzed under the condition of grating length and refractive index change. Because the wavelength change of FBG and strain is linear, structural strain is monitored by wavelength change of FBG monitoring.(2) High speed demodulation system based on double long period grating is studied in order to research dynamic signal monitored by FBG sensor. Double LPFG is consisted of two LPFGS whose center wavelengths are same. Reflection light of FBG modulated by double LPFG is obtained and studied by use of band-hider filter characteristics for double LPFG, and wavelength change of FBG is deduced by light intensity achieved by photodetector.Demodulation system using total fiber technology has the property sunch as compact structure, high precision,linear output.(3) Vibration and impact monitoring method based on FBG network is proposed. Many FBG sensors are used to set up sensing network, which is nervous system of optical fiber smart structure. Impact response signal monitoring is achieved by detecting wavelength change of FBG. Impact different location of structure, impact response signal monitored by FBG is studied.(4)Impact loading localization algorithm is proposed. Feature extraction of acquisition impact response signal is realized with signal energy of different frequency segment using wavelet packet analysis used as characteristic index. Energy corresponding to modal frequency reguarded as sample is imput to Support Vector Machine to set up regression model and impact loading localization of composite speciment is realizated.(5)FBG sensors are applied for health monitoring field of vehicle frame to detect dynamic load states under different conditions. Vibration Conditions of vehicle frame are analysed by experiments of vibration, transient impact and pavement.更多还原