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.