RESEARCH ON FREQUENCY DISPERSION CHARACTERISTICS OF LONGITUDINAL GUIDED WAVE IN MULTI-LAYER TUBE

An extrapolation analysis method based on dispersion characteristics is proposed to solve the problem caused by the dispersion characteristic of guide wave to the test effect of the longitudinal guided wave in a tube. The negative influence is decreased by initiatively selecting the test mode and frequency of the guided wave. Firstly, the Pochhammer-Chree dispersion equation of the longitudinal guided wave in the multi-layer tube is derived through the global matrix method, and a section power flow model, which reflects the degree of the propagating performance of longitudinal guided wave, is also set up. A numerical implementation method to calculate the dispersion characteristics and the section power flow is developed by combining the extrapolation prediction with the double-scale iterative procedure. A method is presented to select the test mode and frequency of the guided wave based on the analysis of computation results. The experiment shows that the results basically coincide with that of the theoretical analysis. The method is useful to choose reasonably test parameters of the guided wave in a pipeline damage test.