同向与反向切变载荷条件下管道中扭转模态导波激励分析

对轴对称多元同向与反向切变载荷施加方式下管道中扭转模态导波T(0,1)的激励问题进行了分析。采用简正模态展开技术,首先分析了不同切变载荷方向下T(0,1)导波的产生机理,建立了导波激励声场与边界载荷的量化关系。在此基础上,结合实验研究,分析了载荷周向分布参数对T(0,1)导波激励的影响,得到了高效激励T(0,1)导波所需的载荷周向分布条件。研究表明,利用轴对称的多元同向切变载荷激励T(0,1)导波是一种实用、高效的方法;而对于多元反向切变载荷则往往要求换能器与管道具备良好的耦合性能。通过优化同向切变载荷的周向分布参数,如增加载荷周向分布角度、减小载荷间隙与宽度比,将有助于获得高信噪比的T(0,1)导波. 

Analysis of torsional guided waves excitation in pipes by co-rotating and reversed shear loading

Torsional guided wave T(0,1) generated in pipes by axisymmetric multiple co-rotating and reversed shear loadings is studied. Based on the normal mode expansion technology, the exciting mechanism of the T(0,1) guided wave under different shear loading directions is advanced and the quantitative relationship between the applied boundary loadings and acoustic field is established. Combined with experimental research, the effects of circumferential loading distribution parameters on the excitation T(0,1) are discussed in detail, and the circumferential loading conditions for efficiently exciting are chose. The results show that the use of axisymmetric multiple co-rotating shear loadings in generation of T(0,1) is a particularly useful and efficient method, but for the reversed shear loadings, excellent coupling performance between transducers and pipes is often required. Furthermore, optimizing the circumferential distribution parameters of the co-rotating shear loadings, with respect to increasing the circumferential loading angles and/or decreasing the ratio of gap width to element width, for example, contributes to acquiring high signal-to-noise ratio T(0,1) mode.