Research On Methods And Key Technologies On High-speed Track Structure Monitoring Based On Fiber Grating

In recent years, the high-speed railway (HSR) in China has achieved remarkable development. This country has the longest kilometers and the highest speed of HSR operation in the world. The safety of operating HSR is of great significance for the national public safety and people’s life. The safety of the track structure is a key point of the safety of HSR. In this country the HSR is high in speed and density in ply. Because this country is large in area, complicated in geographical environment and abominable in climatic conditions, to monitor the track structure of HSR is particularly important. The traditional electrical sensors are used, however, those sensors are short of precision, short of working life, short of signal transmitting under bad environment and unable to establish a large-scale monitoring network. So the research of track structure monitoring causes to make slow progress both in home and abroad.Optical fiber sensing technology has outstanding advantages, such as high accuracy and sensitivity, anti-electromagnetic interference, long life, corrosion resistance and low cost. Among them, the wavelength is used as signal in FBG (fiber Bragg grating) sensing technology. Comparing with the signal of electrical sensor, it has no zero drift. It makes continuously engineering structure monitoring in decades possible.This thesis discusses using optical fiber sensing technology to monitor track structure of HSR. First it analyzes the track structure, and all sensing devices to monitor HSR track structure according to the principle of FBG sensing and demodulating technology have been designed. Then the key monitoring methods and technology suitable for HSR track structure condition have been researched, and then to design the monitoring system. The accuracy and reliability of the monitoring system have been verified by experimental and practical application. Through the applications, valuable monitoring data are obtained. The last work is to analyze the data, and to put out some improving methods of the system. The primary contents in this thesis are as follows:(1) Research of FBG sensing technologyBased on the FBG sensing principle, and on temperature, strain and displacement monitoring needs of HSR track structure, this thesis analyzes these kinds of FBG sensing devices in detail. The technology of temperature compensation of FBG strain sensor and its demodulating method are also introduced. Compared several kinds of optical fiber sensing multiplexing schemes, a sensing web of wavelength division multiplexing (WDM) and space division multiplexing (SDM) methods are structured.(2) FBG sensors design and fabricationThe real-time monitoring significance and necessity of thermal stress and displacement of HSR track structure is defined. According to the research on FBG sensors and track structure, FBG temperature, strain and displacement sensors have been designed and fabricated. The best installation position of rail thermal stress monitoring sensor has been found by rail stress analysis and finite element analysis method. An improvement of FBG temperature sensor has been taken after analyzing the monitoring result to match site temperature monitoring requirement. A new displacement sensor is re-designed, after vector finite element analyzing its structure of strain ring. It received an invention patent. In connection with the safety requirement of HSR switches, a kind of FBG switch point closure monitoring device is created and received another invention patent. It has been demonstrated compliance with the requirements of the railway management.(3) Real-time multi-parameter monitoring on ballastless track structure of HSR sitesA set of on-line monitoring system of HSR ballastless track structure has been designed. In this country, this kind of track structure on-line monitoring is still blank. A bridge in Beijing-Guangzhou HSR and a bridge in Zhengzhou-Xi’an HSR are applied sites. On the former, a high-speed ballastless switch is set on it and needs to monitor. And on the latter, its continuous beam is bent. The application of multi-parameter monitoring has been done including sensor arrangement and data analysis from the sensor from rail temperature, temperature force of three dimensions, displacement between track structure. Another application is on a rail expansion adjuster of an urban rail bridge. The actual monitoring results are of great significance for the structure design, construction of both HSR and urban rail.