基于光纤超声波传感器的桥梁沉降分布式监测技术研究

According to current technical problem and requirement concerning long term on-line gradual settlement monitoring of bridge, a novel distributed optical fiber ultrasonic sensing system will be studied to satisfy the needs of bridge settlement monitoring on long term performance, distributed monitoring, anti-interference capability and high sensitivity. In this proposed research, first, a high sensitive optical fiber ultrasonic sensor system for bridge settlement monitoring will be proposed and investigated, and the settlement response characteristics concerning optical fiber ultrasonic sensors will also be studied and tested experimentally. Then the optical fiber ultrasonic sensing system will be improved accordingly with an aim to optimize its resolution and response capability to high frequency ultrasonic waves. The cross-sensitivity of optical fiber ultrasonic sensing system to temperature and humidity will be studied, and the corresponding compensation technique will also be investigated both theoretically and experimentally to enhance the long term reliability and stability of sensing system. Second, the theoretical and experimental model of bridge settlement will be established through the integration of Finite Element Analysis and experiment. On this basis, the settlement characteristic analyzing and computational model concerning optical fiber ultrasonic sensor will be studied and established, and the corresponding automatic sensing data analyzing and processing system will be developed. Finally, the layout technique of optical fiber sensor will be investigated and optimized based on experiment, and multi-point sensing technique of optical fiber ultrasonic sensing system will also be investigated to achieve long distance distributed on-line monitoring of bridge settlement with a high resolution.

针对目前桥梁缓变沉降的长期在线监测这一技术难题及需求，研究新型基于光纤超声波传感技术的桥梁沉降分布式实时监测技术，以满足桥梁沉降监测对长期性, 分布式, 抗干扰性及高分辨率的需求。根据此思路，首先提出并研究基于高灵敏度光纤超声波的桥梁沉降传感系统，实验研究测试光纤超声波传感器的沉降响应特性，针对性设计并改进光纤超声波传感系统，优化光纤超声波传感器分辨率以及对高频超声波的响应能力，研究解决光纤超声波传感器由于外界温度与湿度变化所产生的交叉敏感问题，并研究其相应补偿技术，提高传感器长期可靠性与稳定性。其次通过有限元分析与试验相结合建立相应的桥梁沉降理论及实验模型，研究建立针对分布式光纤超声传感技术的桥梁沉降特性分析与计算模型，并开发相应的沉降传感数据自动分析与处理系统。最后实验建立并优化分布式光纤传感器布设方案，研究实现光纤超声波传感技术对桥梁沉降的分布式长距离高分辨率在线监测。

针对桥梁沉降长期监测难以及现有监测手段局限性，项目开展了基于光纤超声波传感器的桥梁沉降长期在线监测系统研究, 研究工作及进展如下: .1、研究了多模干涉光纤传感器研究传感机理，设计开发出多模干涉光纤传感器并实现对25kHz以上高频超声波的探测。通过abqus有限元模拟结合试验揭示了传感器膜片与灵敏度之间响应规律，通过优化设计进一步提高了光纤传感器对高频超声波的响应灵敏度,其探测灵敏度提高3倍。 .2、设计搭建了光纤超声波非接触式位移探测系统,成功实现对7米范围内位移的超声波探测. 在此基础上提出并实现了双传感器信号参考技术实现对位移的高精度探测,消除外界环境以及系统自身噪声对传感系统影响。 .3、提出并采用连续波相位分析法实现光纤超声波传感器实现对位移非接触式测量，位移分辨率达到0.2mm但其缺点是量程小。 .4、提出并实现了基于双传感器脉冲探测法的位移传感方案，用于克服连续波相位法量程有限的缺点，实现了对位移变化的大量程非接触式探测，但位移测量精度较低，仅为2mm。 .5、首次提出并研究了一种新型基于脉冲-相位探测法的高精度、大量程位移传感方案，突破脉冲探测法精度低以及连续波相位探测法量程小的技术瓶颈，在实现大范围位移测量的同时，保证其测量高精度的要求，其测量分辨率达0.3mm以上，位移探测量程可达7米以上。.6、深入研究了双平衡微波鉴相技术并设计开发出了集成化硬件鉴相解调模块，实现对动态位移所引起传感器信号相位变化的实时探测与解析。 .7、结合桥梁工后沉降特点，设计并实施了模拟桥梁沉降的测试试验，所开发传感系统沉降监测试验重复性达到0.4mm以上。 .8、基于以上研究拓展提出并试验实现了分布式光纤超声波传感对三维位移变化的测量.该课题实现并验证了光纤超声波传感技术用于桥梁非接触式沉降监测的可行性，一方面为解决实际工程问题提供了新思路与研究基础；另一方面通过结构健康监测与光纤传感之间学科深度交叉与融合，促进了相关学科及前沿技术发展。