Research On Spectral Method For Exploring The Propagation Characteristics Of Axisymmetric Ultrasonic Guided Wave In Pipe

This dissertation, in which the research work focused on the topic-spectral method on exploring the propagation characteristics of axisymmetric ultrasonic guided wave in pipe, was mainly supported by the High Technology Research and Development Program of China ’Research on the condition monitoring and fault diagnosis technique and its application software system of supercritical and ultra-supercritical steam turbine generator unit’(No.2008AA04Z410) and the National Natural Fund Project ’Dynamic monitoring and failure pre-warning for vibration signals in pipelines conveying multiphase flow’(No.11072213). This study consists of the new rapid calculation for obtaining the ultrasonic guided wave propagation characteristics accurately and efficiently; the pipe ultrasonic guided wave propagation equations under the influence of high temperature and weak interface and the optimized method about ultrasonic guided wave defect detection parameters based on obtained propagation characteristics. Both piezoelectric and magnetostrictive detection prober aiming for ultrasonic guided wave inspection, high voltage broadband ultrasonic power amplifier and the experiment platform for pipe to study ultrasonic guided wave propagation characteristics are designed and constructed. All theoretical approaches listed above were testified by either numerical simulation data or experimental data obtained from the developed detection system.The scheme of this study is organized as follows:In Chapter1, the ultrasonic guided wave inspection in pipe makes great sense to secure working medium delivery systems in the energy production and transportation industry. The derivation and analysis of guided wave propagation characteristic play an important role in the defect detection. The state-of-art of pipe ultrasonic guided wave propagation characteristic was reviewed. Current problems and challenges of pipe ultrasonic guided wave propagation characteristic study were deduced from next two perspectives:the academic solution of pipe ultrasonic guided wave propagation characteristics and the corresponding experiment and detection systems. Then, the main content, together with the scheme and innovation points of this dissertation was given.In Chapter2, axisymmetric guided wave propagation equations for single-layer and multi-layer pipe were deduced based on the kinetic theory of elasticity, the superposition principle of partial bulk waves and the global matrix method. An improved root-finding approach was developed by combining the extrapolation prediction and the double-scale iterative procedure. And a corresponding program flow was designed to explore guided wave dispersion characteristics and wave mode shapes. With the analysis of traditional displacements and stresses which vary through the thickness, a section power flow model was set up which reflected the degree of propagating performance of guided wave. For minimizing the negative influence of guided wave dispersion characteristics and multi-mode, an optimized method of guided wave testing parameters for piping defect detection was studied based on the analysis guided wave propagation characteristics. Theoretical analysis approach was verified by characteristic data analysis from numerical example.In Chapter3, a more efficient analysis approach for exploring propagation characteristic of axisymmetric guide wave in pipe was proposed by using the spectral method to relieve the low efficiency by using of traditional root-finding approach, and a corresponding graphical user interface program based on spectral method was also designed to facilitate the analysis by considering the high temperature influence. Numerical validation studies of two kind pipes at normal and high temperature environmental conditions were carried by both spectral method and iterative root-finding approach. Traditional two-dimensional displacement wave shapes was improved to the forms of three-dimensional displacements on varying through the thickness and frequency, which greatly improve analysis result of wave mode shapes. Finally, with the help of obtained dispersion characteristic curve and three-dimensional mode shapes characteristics, the advantages of spectral method for obtaining guided wave propagation characteristics were verified, so did the axisymmetric guided wave testing parameters optimization by considering the temperature influence.In Chapter4, since current analysis method of ultrasonic guided wave propagation characteristics is insufficient in precision and efficiency, an improved spectral-root finding approach for the derivation of guided wave propagation characteristic was proposed which preserves both the efficiency and the accuracy. The corresponding graphical program was then designed to facilitate propagation characteristic analysis by taking consideration of weak interface influence. The axisymmetric guided wave propagation characteristics under two interface conditions were successfully obtained and drawn, and the advantage of this improved approach was analyzed by comparing propagation characteristics from iterative root-finding approach, spectral method and this approach. Finally, the weak interface impact analysis of two-layer pipe and the detection parameters optimization of axisymmetric guided wave for two-layer pipe were discussed based above obtained propagation characteristics.In Chapter5, the overall ultrasonic guided wave inspection system architecture was designed based on the requirement analysis of pipe ultrasonic guided wave propagation characteristics experiment and main technical performance were also specified. Some key technological studies of pipe ultrasonic guided wave propagation and detection system were carried out. Magnetostrictive transmit prober, piezoelectric receiving prober and high voltage broadband power amplifier customized for guided wave defect detection were developed. The corresponding performance testing and optimization of above components were synchronously implemented. Finally, both defect detection system performance and above-mentioned theoretical analysis method were validated based the experiment platform.In Chapter6, the conclusions were made and some advanced topics which need further investigation were presented.