管道弯头对低频纵向导波传播特性影响分析

管道弯头显著改变了导波传播特性,影响了对检测信号的解读,研究弯头对导波传播特性的影响是实现复杂管道系统导波检测的基础。采用半解析有限元法计算弯管导波频散曲线,分析了弯管导波频散曲线所呈现的不同特征,并基于弯管导波频散曲线,以低频L(0,1)模态导波为研究对象,实验研究了低频L(0,1)模态导波通过管道弯头时的模态变换特征。研究结果发现,当L(0,1)模态导波通过管道弯头时,不仅会发生L(0,1)到F(1,1)的模态变换,还会模态变换出反向L(0,1)模态导波,即弯头反射现象,且随着激励频率的降低和弯头弯曲半径的减小,弯头反射现象愈发明显。研究结果将深化对弯管导波传播特性的认识,推动导波检测技术在复杂管道系统检测中的应用。 

The effect of pipe bend on low-frequency longitudinal mode guided wave propagation

The pipe bend will significantly change the propagation characteristics of guided wave, and make the interpretation of detected signal difficult. So, the effect of pipe bend on the propagation characteristics of guided wave should be the key to the detection of complicated pipeworks. First of all, the features of dispersion curves for bended pipes, which are derived with the semi-analytical finite element method, are summarized. Secondly, based on the dispersion curves for bended pipes, experiments of bended pipe detection have been conducted to show the mode conversion of L(0, 1) mode guided wave due to pipe bends. It is found that, except for the L(0, 1) to F(1, 1) mode conversion, the L(0, 1) reflections of bends are also observed in some cases, which has been proven to be the negative L(0, 1) mode guided wave mode converted from the incident L(0, 1), and the negative L(0, 1) mode guided wave becomes more obvious with the decreasing of excitation frequency and bend radius. The study results will deep the understanding for propagation characteristics of guided wave in bended pipe, and generalize the application of guided wave detection in complicated pipeworks.