Strain Measurement And Modal Analysis On Pipeline Based On Fiber Bragg Grating Sensing

Pipelines are prevalent in many fields, including aerospace, energy industry, chemical industry, etc. But the failure of pipelines, caused by vibration fatigue, influences the safe operation of pipelines seriously. At present, on aspect of measurement of pipeline vibrating, especially in strain measurement, the common sensors own the problems such as difficulties in distributed detection, influence of added mass, large size, uneasy installation, electromagnetic interference, leading-out cable complexity, etc. The fiber Bragg grating sensors(FBGs), as a new kind of sensor, can overcome these problems above very well, and is appropriate for strain measurement on the pipeline.In this paper, the strain measurement and modal analysis on the pipelines within light weight and small size are finished through FBGs and many theory-guided experiments. Firstly, based on theories of pipeline vibration and strain modal analysis, experimental researches are developed on strain measurement and modal analysis of pipeline using FBGs and obtained data. Secondly, the accuracy and superiority of FBGs are proven by the compared experiments. At last, FBGs are applied to strain measurement and modal analysis on pipeline of the engine. In this paper, the main works include:1. The frequency equation is established to acquire the natural frequency of pipeline through the transfer matrix and boundary condition. The calculated natural frequencies of one liquid-filled straight pipe and the other L-shape pipe are compared with the results of ANSYS simulation, which proves the accuracy of this equation and its solution.2. An improvement on the operational modal parameter identification is realized by replacing constructed polynomial with rational fraction of response, in order to identify poles of system. This method overcomes the big number in the pole of constructed polynomial, which is greater than poles of system. Meanwhile, the M-file of this algorithm is written by MATLAB.3. Experiments on stainless steel pipes are done based on FBGs, the strain measurement and modal analysis provide a lot of data. And then strain modal parameter is obtained by experimental modal analysis and operational modal analysis respectively. The results indicate that the experimental results are consistent with the theoretical values, and it is feasible to utilize FBG on strain measurement and modal analysis on pipeline.4. FBGs are utilized on strain measurement and modal analysis on pipe of the engine, and the measured parameters, including natural frequency and strain modal shape, meet with the theoretical values. Meanwhile, the results of FBGs are accurate and valid through comparison to that of accelerometers. Furthermore, FBGs are capable of reflecting the actual characteristics of pipelines because of its negligible mass, which is better than the added mass of accelerometer leading to decreasing of natural frequency of pipeline. At last, FBGs supply the pipeline of the engine with strain measurement, modal analysis and strain modal parameters, when the engine is in static condition.