基于SBS原理的混凝土坝裂缝分布式光纤传感研究

Accumulative damage real-time identification and monitoring has been a key difficult issue in structural health monitoring.Fibier optic sensing based on Stimulated Brillouin Scattering（SBS） is a frontier technology,and plays the leading role in application reaseach into distributed structure damage detection.As a technique the sensing optical signal of which is adjusted by strain,when it is applied to structural crack monitoring, high concentration of strain along optic fiber around crack occurs ,and complicates distortion of optic signal greatly so that the formation and widening of crack can't be detected sensitively, and the crack width can't be determined, thus limiting its practical application to real engineering.. Based on considerably improved spatial resolution of this technique, and according to interface mesomechanical mechanism within concrete and optic fiber (mutiple contings –optic fiber core)complex, complex structure of fiber optical sensors is designed to control local strain distribution along optic fiber near crack,so the normal form of the optical signal is maintained, with a view to developing a simple and easy method by which dynamic and quantitative observation of cracks within concrete is implemented as well as theoretical basis for sensor design and signal analysis in its engineering application to distributed monitoring of concrete cracks.. Adjustment and control of sensing optical route is adopted to measure single-valued width of spatially occurring random cracks within structures ,aiming to make this technique systematically meet the requirements of large dam safety monitoring.. Spatial topological sensing network distributions based on fiber optical SBS are also formulated for common types of concrete dams.

工程结构损伤破坏的实时识别和监测,仍是结构监测健康中的关键难题。基于受激布里渊散射（SBS）原理的光纤传感,为当前分布式传感领域的前沿技术,并在相关应用研究中居主导地位。作为一种感应光信号受应变调制的传感技术,裂缝附近传感光纤应变分布的局部集中,会极大加剧感应光信号的畸变,以致对裂缝的感知欠灵敏及定宽难,因而限制其工程应用。项目基于该技术改善的空间分辨率,利用混凝土-光纤（多层涂覆-纤芯）复合体界面细观力学机制,通过调制传感器的复合结构,控制裂缝附近传感光纤的应变分布,从而保持光信号的正常形态,以建立该技术可对混凝土内部裂缝形成与扩展全过程动态、量化观测的简易方法,及其在工程应用中传感器设计和信号分析的理论基础。项目提出基于传感光路调控方法,对结构空间随机裂缝宽度进行分布式单值测定研究,旨在系统实现该技术满足大坝安全监测的需要。项目还构建基于SBS原理的典型混凝土坝光纤裂缝传感空间网络。

基于受激布里渊散射（SBS）原理的光纤传感技术的代表主要是布里渊光时域分析技术BOTDA。本课题采用BOTDA技术对混凝土裂缝进行监测研究，分析混凝土-光纤界面滑移-脱黏过程与机制，给出光纤拉伸-滑移-断裂力学机制并建立相关力学模型，得出不考虑及考虑界面脱黏的光纤参数与缝宽及灵敏性之间的解析关系，并将理论结果与监测结果进行了对比。虽然 BOTDA的空间分辨率大为提高，但裂缝附近传感光纤应变分布的局部集中，会使感应光信号产生畸变，本课题采用高弹性模量的光纤涂覆层来提高灵敏度并改善应变局部集中导致的测量结构的多值性，从而改善由于信号畸变产生的偏差。. 本课题旨在进行混凝土坝裂缝分布式光纤传感研究，对于大坝等大型结构的安全监测存在由于光纤损耗会导致信噪比降低、传输效果不好等情况，课题组给出了提高信噪比的方案。该方案具有高适应性和降噪性能，从而满足大坝安全监测的需要。. 控制时序和步距方面，经过课题组研究，建立结构空间随机裂缝传感光纤全光路动态调控机制，构建实时、灵敏光路调控系统 （ORAS)，利用光开关等光电器件，实现对结构控制不同位置随机裂缝宽度的分布式单值测定，为建立光信号感应参量即光频移与裂缝宽度等特征参量之间的单值量化关系建立实验测试手段，整体实现基于SBS原理的光纤技术对混凝土开裂过程的动态监测。