Research On Pipeline Deformation Sensing Based On Weak FBG Array

With the high efficiency of transmitting liquid,pipeline is widely used in various production scenarios.Long-term health monitoring of long-distance transportation pipelines requires stable monitoring technique es due to the complex environmental conditions.Distributed optical fiber sensing technology has the characteristics of high temperature resistance,corrosion resistance and strong anti-interference ability.Through applying the technology,super-large range and super-large capacity distributed sensing at low cost can be achieved,which is suitable for structure monitoring of pipelines.Aiming at the problem of pipeline deformation,the thesis combines distributed weak grating sensor array with fiber shape sensor to carry out relevant research on the overall shape measurement of pipeline.The main contents and conclusions are as follows:1.The study applied static theory and finite element simulation to analyze the elastic deformation within the scope of the rigid pipe structure under different deformation modes of the stress distribution,The thesis focused on the strain distribution model of pipeline structure surface under bending deformation,and verifies the distribution law of pipeline surface strain under bending according to sine function.2.In the thesis,a pipeline deformation sensing technology scheme based on weak grating sensor array is proposed to realize the three-dimensional shape sensing of long-distance continuous pipelines by utilizing the characteristics of large capacity and high spatial resolution of weak grating array.Combined with mechanical and geometric models,the principle of measuring the curvature and bending direction of the pipeline by optical fiber is deduced.A curvature reconstruction algorithm was proposed to construct the three-dimensional shape of the pipe axis curve from the curvature data.A visualization method is designed to restore the whole 3D model of pipeline from the curve of pipeline axis.In Matlab software,the algorithm is used to simulate the random spatial curvature data and realize the visualization of the pipeline axis curve and the overall three-dimensional shape of the pipeline.3.An optical fiber shape sensing device is designed and fabricated for pipeline.A geometric model was constructed with the sensing fiber on the device.The sensitivity of measuring axial strain of pipeline is simulated and analyzed by numerical simulation method,and the conclusion is drawn that the sensitivity of measuring axial strain of pipeline decreases significantly with the increase of inclination angle in0-180° period.4.The thesis proposed an image processing algorithm for measuring the curvature of pipe axis,combined with machine vision and optical fiber shape sensing technology,designed a calibration method and experimental platform.In this method,a series of six weak grating sensor arrays were used to calibrate 0.5m pipelines with sensing fibers arranged in directions of 0°,60°,120° and 180°.The measurement accuracy of the bending azimuth angle of the pipeline shape sensor device was up to±5° when the fibers were arranged at different angles.The average curvature measurement accuracy can reach ±7% according to the calibration coefficient when the optical fibers are arranged in axial direction.5.Multi-direction bending experiments are carried out to simulate the continuous pipeline,and 3D visualization of the overall shape of the continuous pipeline is realized by using the optical fiber shape sensing system,which verifies the measuring ability of the quasi-distributed optical fiber deformation sensing technology proposed in this thesis.