| Rail transport is an important lifeline of a country. Its safety operation is therefore crucial for public security, social stability, and it is even involved to accelerate national economy progress of this country. Safety operation and sustainable development of rail transport engineering structure have become an imminence requirement of national strategy.Effective methods of health monitoring and security warning of rail transport engineering structure should be developed. However, China is vast in territory and its geological environment is complicated, rail transport system stretches across vast area covering cold, temperate and tropical zones. So Chinese rail transport system needs a better monitoring system with multi-role performance than a small European country does.Electrical sensors are widely used now, but they have a lot of defects, such as zero drift, and under complex environment, they are prone to be out of order, and they are hard to develop a large scale sensing network, for its short transmission distance. Under these circumstances, there are theoretical and technical bottlenecks to apply electrical sensing technology in the area of rail transport monitoring.Fiber optical grating sensing technology provides an effective approach to solve these problems. Unfortunately, in this country, there is a lack of comprehensive and systematic study in dynamic safety monitoring of rail structure with optical fiber sensing, to say nothing of the study of monitoring high speed ballastless railway structure.In view of the above problems, and based on the advantage of interdisciplinary, including optical fiber sensing technology, detection technology and rail transport engineering technology, in this thesis, the wheel/rail coupling condition has been analyzed, and fabrication technology of fiber grating sensing devices have been introduced. This thesis also introduces some optical fiber sensing network systems which realize monitoring rail structure state and dynamic state in real-time. They are respectively optical fiber sensing block system, overload and unbalanced load monitoring system, wheel damage identification system, and high speed ballastless rail multi-parameter monitoring system. And these research achievements have been applied on the railway. The major research contents are expressed as followings:(1) Building of vehicle model and rail modelThe vehicle model is built according to the characteristics of vehicle, rail model is a model of continuous elastic discrete point support. Explicit integral method is adopted for vehicle numerical value simulation, and vector finite-element method is also adopted for rail numerical value simulation, both rail and vehicle numerical value simulation can be integrated by Hertz nonlinear elastic contact theory. The change of rail strain is obtained under different speeds and load, and the results showed that the maximal amplitude of axial strain of the rail is382.6με under axle load of40tons, and19.1με under a axle load of2tons. The3dB width of the strain signal was about6ms when a train passed at a speed of350km/h. The results can provide direct reference for designing the range and solution of sensors, and for designing the sampling frequency of instruments.(2) A novel sensing demodulating approach based on CFBGThe sensing principle of CFBG is expounded. It bases on the sensing principle of FBG, and its sensing demodulating approach is introduced. This demodulating approach adopts a power detection way, and reduces the cost without expensive F-P filter. The demodulating approach is characterized by high-speed because the speed of photo-voltaic conversion is very fast. This approach is a complementary way comparing with the mainstream FBG demodulating method.(3) Development of rail state optical fiber monitoring systemsThe necessity of three monitoring parameters are analyzed, including wheel-rail coupling vertical load, thermal stress and temperature of rail, displacement between rail and its sleepers. Several sensing devices are designed to meet the different requirements, including FBG strain gages, FBG temperature gages and FBG displacement sensors. The sensing network combines WDM method and SDM method to setup a multi-channel and high-capacity FBG network. Software function realization and its process are discussed on the basis of the function and sensor arrangement of each monitoring system.(4) Establishment of railway blocking systemBlocking system is established which based on wheel-rail coupling vertical load detector. Aiming at key problems of real-time axle counting, which is caused by train stopping and reversing, a counting algorithm is found through repeated analysis and field tests. This algorithm could even solve more complicated counting problem by combing three axles counting devices. An experiment site is established on the Zhifang train station of Beijing-Guangzhou railway line, and the error rate of counting result is less than1/200000.(5) Train overload and unbalanced load monitoring systemThe framework of hardware and software are discussed to meet requirements of overload and unbalanced load monitoring. Determination method of overload and unbalanced load is introduced. According to the experimental data analysis, a method for extracting wheel load information is found based on wheel-rail coupling vertical load device. The device can be fixed directly on the rail without breaking rail structure, the experimental results show that the error margin of weighing is less than4.0%under20km/h train speed, without reinforcing ballast rail base. As for wheel damage judgment, measurement record is decomposed by EMD and IMFs are obtained to decide damage indices of wheels.(6) High speed ballastless rail monitoring systemAccording to the characteristics of high-speed railway switch with ballastless slab on Leida bridge, the arrangement of fiber sensing monitoring system is designed based on thermal stress detector, temperature detector and displacement detector. The system is installed and some valuable data were obtained. This is a matter of great significance to introduce FBG sensing technology first time into ballastless rail monitoring. The change of the ballastless rail state can be got to provide reference for designers and managers. |
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