Research On Fiber Bragg Grating Sensing Theory And Key Technology For Linear Engineering Deformation Field Monitoring

In recent years,the construction of facilities in China has developed vigorously in the fields of railway,highway,water conservancy and hydropower,municipal engineering,etc.A large number of major linear projects,such as high and steep slopes,long-span bridges,reservoir dams,deep and long tunnels,have been put into construction or operation.Linear engineering is characterized by long longitudinal length,small horizontal distribution,wide distribution range,long service time and complex operation environment.Due to the influence of hydrology,earthquake,material corrosion aging,construction quality,improper operation management and other factors,some engineering facilities have unsafe factors such as cracks and lesions,which affect the performance of engineering benefits to varying degrees.Long time fatigue and unhealthy operation lead to frequent accidents,which cause a large number of casualties and huge economic losses,seriously restricting economic construction and social development.According to the characteristics of linear engineering disaster,such as strong emergency,serious accident consequence and concealment in the early stage of disaster,it is the key measure to effectively ensure the safe operation of linear engineering and reduce the occurrence of disaster to study the high-precision state monitoring and sensing theory applicable to linear engineering structure and develop advanced monitoring equipment and measuring system.Optical fiber sensing technology has the advantages of high measurement accuracy,strong multiplexing ability and long signal transmission distance,which is favored by researchers at home and abroad.But at present,the fiber grating sensing technology for safety monitoring of linear engineering structure still has some shortcomings.Most of the FBG sensors can only monitor the mechanical parameters such as inclination,displacement,pressure and strain that are related to the stability of engineering structures with the point-mode.They are not suitable for measuring the displacement field of the whole structure and positioning the deformation surface.There are few researches on the factors that cause the measurement error of FBG sensor such as the strain transfer efficiency between the sensor point and the flexible matrix,the placement interval of the sensor point,the shape reconstruction algorithm and so on,as well as the improvement of the sensor performance.The research on the flexible sensor with the functions of reinforcement and sensing and the high-precision sensing of the three-dimensional deformation field is insufficient,which can not realize the comprehensive analysis and accurate early warning of various parameters.Through the above discussion and analysis,this paper takes the high-precision sensing of linear engineering deformation field as the application background,and relies on the model test and field application of different disaster types(such as slope slip,subgrade subsidence,bridge settlement,dam deformation,etc.).The reason of the shape reconstruction error of FBG sensor is analyzed theoretically,and the correction method based on the self-classification and self-clustering of bending shape is proposed.A flexible FBG sensor is developed for two-dimensional and three-dimensional deformation field monitoring of linear engineering.The necessity and feasibility of the proposed correction method are verified by finite element simulation analysis and calibration experiments.Model test and field application are carried out to analyze the performance of the designed sensor.The specific research work is as follows.1.Based on the coupled mode theory and the transfer matrix theory,the spectral characteristics of different gate length,axial uniform stress and non-uniform stress are studied.Theoretical derivation and modeling are used to analyze the influence of the bonding mode(bonding length,width and thickness),the characteristics of the flexible matrix,and the placement interval of the sensing points on the deformation shape reconstruction accuracy of the flexible sensor.Guide the fabrication and packaging of sensors through theoretical analysis,and the necessity of realizing high precision deformation sensing.2.The reconstruction algorithms for two-dimensional and three-dimensional deformation fields of linear engineering are studied and analyzed.According to the different bending deformation of flexible sensor,a method of high-precision sensor based on the classification correction of bending shape is proposed.The typical bending shape of flexible sensor is calibrated by experiment.The intelligent classification algorithm is used to classify the bending shape of sensor automatically,and then the corresponding correction coefficient is selected automatically for different bending shapes.The feasibility and necessity of the application of the high-precision sensing method based on shape self classification in two-dimensional and three-dimensional deformation fields are verified by simulation analysis and calibration experiments.3.Aiming at the variety of deformation field of linear engineering structure,a high-precision deformation field sensing method based on shape self clustering is proposed.Taking the strain increment at the sensor point as the characteristic value,the cluster algorithm is used to cluster the variable increment,and then the deformation segments with different bending shapes of the flexible sensor are identified automatically.Then the optimal correction coefficient of different deformation segments is determined by the optimization algorithm,which has the characteristics of automatic correction and reconstruction of displacement field.Through simulation analysis and calibration experiments,the high-precision sensing method of deformation field based on shape self clustering is proved to be effective in the application of two-dimensional deformation field and three-dimensional deformation field.4.The multi-parameter measurement of linear engineering structure is realized,which can reflect the safety state of the tested structure comprehensively.The FBG crack sensor with novel structure and the fiber-optic humidity sensor for monitoring the ambient humidity of the project are developed.In order to meet the actual engineering needs,improve the survival rate of FBG sensing points and reduce the production cost of the sensor,a traction type flexible FBG sensing system is designed,and a mesh flexible FBG sensor with reinforcement and deformation sensing is researched and manufactured.The model test is carried out to verify that the designed flexible sensor can achieve high-precision sensing in linear engineering monitoring such as subgrade settlement,bridge deflection,slope deformation,etc.The designed crack sensor and three-dimensional flexible sensor are respectively applied to the anti-debonding monitoring of concrete-filled steel tube and the safe operation monitoring of dam,which can monitor and forewarn the tested structure in real time to ensure the safe and efficient operation of the project.In this paper,effective research and development and performance optimization of sensors for linear engineering monitoring are carried out.In the aspect of application:monitor the deformation of engineering structure to find out abnormal changes in time,and judge its stability and safety,so as to take remedial measures to prevent accidents in time.In the aspect of scientific research:accumulate and analyze the monitoring data to better explain the deformation mechanism,verify the deformation hypothesis,and provide the basis for later modification of design and formulation of design specifications.