Research On Temperature-sensing Mechanism Of Distributed Optical Fiber And Application On Pipeline Leak Detection

Pipeline transportation,as an important means of conveying liquid and gaseous materials,has been widely used in various industries.With its great impact on the life,construction and development of modern society,pipeline transportation also brings huge security challenges,among which pipeline leakage is one of the persistent diseases that has affected the safety of pipeline transportation for a long time.Therefore,much attention has been paid to the research and application of an effective pipeline leak detection method.Currently,various technical means have been developed and the distributed optical fiber pipeline leak detection technology,based on the sudden change of local temperature of leak point stands out with its technical advantages such as wide monitoring range,high real-time performance,low cost and excellent on-line monitoring ability,and has become one of the most promising leak detection methods in pipeline transportation.However,there are still some challenges in this method in terms of temperature measurement accuracy and spatial resolution,as well as the identification of temperature variation causality,that is,temperature field decoupling.Based on the above background,this dissertation has proposed to study the distributed optical fiber temperature sensing mechanism and its application in pipeline leak detection.On the basis of a systematic understanding of optical fiber transmission characteristics and distributed optical fiber temperature sensing mechanism,this dissertation focused on the study of key technologies such as improving optical fiber temperature measurement accuracy and spatial resolution as well as its temperature field decoupling,and developed a high performance optical fiber temperature measurement technology based on laser coding and interval calibration,and utilized fuzzy neural network to realize the classification and recognition of complicated coupled temperature field,and at the same time,developed a pipeline leak detection system based on distributed optical fiber temperature measurement,and carried out some related experiments and applied research.The main contents and innovation are listed as follows:Chapter ?,the significance of pipeline material transportation and pipeline leak detection is expounded and the research status and development trend of distributed optical fiber temperature measurement and leak detection technology are systematically understood.This paper analyzes the problems of distributed optical fiber temperature measurement technology for pipeline leak detection,points out the direction of this research,and arranges the research contents of each chapter.Chapter ?,the optical fiber transmission characteristics and the distributed fiber temperature measurement mechanism based on Raman scattering are analyzed,and the theoretical modeling of distributed fiber temperature measurement is realized.At the same time,on the basis of determining the function and performance objectives of pipeline leak detection system,the overall scheme of pipeline leakage detection system based on distributed optical fiber temperature measurement is designed and the key technologies to be solved are condensed.Chapter ?,the high performance temperature measurement technology of distributed optical fiber is studied.Based on signal preprocessing by sampling integral,laser pulse coding is used to optimize the spatial resolution,and the temperature measurement accuracy of distributed optical fiber is effectively improved by using interval temperature calibration and multistage fitting model.Chapter ?,the research of temperature field recognition technology based on fuzzy neural network is carried out.According to the gradient characteristic of temperature field and the correlation analysis of temperature signal,Hottling transform is used to extract the characteristic parameters of the temperature field.As for the fuzziness of temperature coupling factors,on the of Takagi-Sugeno fuzzy neural network structure and its learning algorithm,a temperature field recognition technology based on fuzzy neural network is developed to realize the recognition of complex coupled temperature field and the causality of pipeline local temperature sudden change is effectively clarified,thus improving the robustness of pipeline leak detection.Chapter ?,by taking distributed architecture,modular design strategy,and by using optical fiber as temperature sensing components and on the basis of developing hardware modules like laser signal transmission,reception and digitization as well as related software modules.An integrated pipeline leak on-line detection system based on distributed optical fiber temperature measurement is developed,and experimental research is carried out to reach the practical level.Chapter ?,research contents and achievements of this paper is summarized and prospects of next research stage is proposed.