Study On The Modeling And Location Process Of The Distributed Fiber Oil And Gas Pipelines Pre-warning System Based On Double Mach-Zehnder Interferometer Structure

As an important means of transporting oil and gas resources, the length of pipeline is growthing rapidly due to the development of oil and gas industry and consumption. And people pay more and more attention to pipleline's security issues. The distributed optical fiber oil and gas pipeline security pre-warning system studied by our research group, can perform pre-warning monitoring and locating the abnormal dangerous events that happens nearby the oil and gas pipeline.so that the pipeline administrative staff could take preventive measures to stop threatening events to avoid safe accidents. This will bring great social and economic benefits.In the system experitments, the correlation of the two signals, which are used in location process, is often in the state of random variation. This will lead large location error, and affect the stability of the system operating. In this paper, the system's Jones matrix model and the location process are deeply studied. The main contents are as follows:(1) The polarization properties of single-mode optical fiber are studied, and then the single-mode fiber Jones Matrix model is established. The model of the system is established using the single mode fiber model, and then the model simulation is analyzed to find the reasons of phase shift and polarization fading. Phase shift is the the mainly cause of large location error.(2) Based on the Jones Matrix model, an active phase shift compensation method, which uses a polarization controller to control polarization states of output light, is proposed. The global search algorithm and simulated annealing algorithm based on the correlation coefficient of two signals are studied, and then some key parameters, such as the initial temperature, the maximum step length, the temperature update constant, are determined through the experiment. The on-site experiment shows that the two polarization control algorithms can stabilize the correlation between the two detection signals. But the simulated annealing method has faster response speed and greater control efficiency than global search method.(3) Based on the Jones Matrix model, a phase passive soft demodulation solution using 3×3 couplers is proposed. By this soft demodulation, both clockwise and counterclockwise signals are demodulated to estimate the time delay. The on-site experiments show that this method can improve location accuracy, maintain long-term stable operation of the system.(4) A time delay estimation method for locating the pipelines invasionevents, based on third-order cumulant and adaptive filter is proposed. The third-order cumulants and adaptive filters algorithm for time delay estimation are studied.In order to improve the events locating accuracy and consistency, the third-order cumulant is used to abate Gaussian coherent noise, and the adaptive filter is used to abate non-Gaussian coherent noise and get time delay estimation.(5) Two kinds of distributed fiber oil and gas pipeline safety pre-warning system are developed and installed on the actual long-distance pipeline. The on-site experiments and long-term operation results show that the methods proposed in this paper can ensure the system operating with long-term stable and effective.