Study On Multi-parameter And Dynamical Measuring Method Of Hydraulic Pipeline Based On Fiber Bragg Grating Sensing

For large-scale key equipment in mechanical,aeronautic & astronautic,oil and chemical engineering fields,safety accidents happen frequently caused by the damages like leaks and fractures in hydraulic pipelines in high-temperature,high-pressure,and strongly vibrated environment.Due to the couple effects of multi-physics fields,including mechanical field,thermal field,and flow field,hydraulic pipeline is mutable,interacted and nonlinear with a complex and variational theoretical model,which induces that its theoretical calculation is difficult.Theory research and experiment research should be combined.However,traditional measuring technologies cannot satisfy the requirements of multi-parameter dynamical measurement of hydraulic pipeline.Therefore,in order to break through the limitations of traditional measuring technologies,the research of new multi-parameter dynamical measuring method based fiber Bragg grating sensing is of great significance to dynamic characteristic analysis,optimization design,condition monitoring and fault diagnosis for hydraulic pipeline.Through analyzing working characteristics,failure reasons,and measuring technology and method of hydraulic pipeline,the research of multi-parameter dynamical measuring principle,technology and method based on Fiber Bragg Grating(FBG)sensing,has been conducted in this paper.The main research results are as following:(1)Concerning multi-parameter dynamical measuring principle and technology of hydraulic pipeline,principles of FBG sensing for multi-parameter measurement and pressure enhancement are studied,and temperature compensation technologies of reference FBG and differential are proposed.Through studying strain modal analysis model and method,the basic model and measuring method of strain transfer function matrix are given.Based on the research of strain measuring principle and method for hydraulic pipeline,comparative experiments have been carried out between FBG sensors and traditional electric sensors.Experimental results show that FBG sensors are immune to electromagnetic interference,and have little effect on measuring results of dynamic characteristics of hydraulic pipeline.(2)For temperature measurement of hydraulic pipeline,the temperature sensor packaged by ceramic tube for temperature measurement of oil,and the plate-type temperature sensor installed by magnets for structure's surface temperature measurement have been proposed.For multi-point dynamical pressure measurements in hydraulic pipeline,a kind of C-type pressure sensor,a novel strain diaphragm-type pressure sensor,and a displacement diaphragm-type pressure sensor,have been developed by studying pressure enhancement principle and temperature compensation method.Experimental results show that the accuracies of the developed FBG pressure sensors are high,and the diaphragm-type FBG pressure sensor could be used for dynamical pressure measurement for its wide measuring frequency range.In addition,another two kinds of new FBG pressure sensors(an easily connected pressure sensor and a sensor for pressure and temperature simultaneous measurement)have been presented for multi-point pressure measurements in hydraulic pipeline.(3)Concerning multi-parameter dynamical measuring method of hydraulic pipeline,identification method based on orthogonal polynomial method for system poles,and least squares method in frequency domain for modal shapes,have been proposed by studying modal parameter identification method for hydraulic pipeline.Experimental results indicate that the presented method based on FBG sensing provides a new way for strain modal measurement of hydraulic pipeline.By investigating measuring method of exciting force,a new FBG force hammer for experimental modal analysis has been developed.(4)Considering the main failure modes of hydraulic pipeline,a new vibration experimental platform has been built for multi-parameter measurement to simulate vibration environment and obtain various parameters,such as temperature,pressure,acceleration,strain and flow.Based on the research of multi-parameter dynamical measuring principle,technology and method,a multi-parameter dynamical measuring system has been proposed for hydraulic pipeline based on FBG sensing.Comparable experiments have been carried out between this system and the traditional electric measuring system.Experimental results show that the proposed system possesses a good anti-electromagnetic interference ability and high measuring precision for multi-parameter dynamical measurement of hydraulic pipeline.(5)The proposed multi-parameter dynamical measurement system based on FBG sensing for hydraulic pipeline,was adopted to measure dynamical responds of aero-engine's pipeline to obtain its vibration strain and strain modal parameters.By studying the principle and method of leakage detecting and wire breakage,a remote online condition monitoring and evaluating system based on FBG sensing has been proposed for prestressed concrete cylinder pipeline.The results of field experiments indicate that the presented system could be applied to monitor leakage and wire breakage,effectively.