Investigation of transient process in a cylindrical wave guide for Lamb waves

Abstract

A transient process in cylindrical wave-guide was simulated and experimentaly investigated. The antisymmetric Lamb waves zero order were excited by point-form transducers: one or two placed on opposite sides of the cylinder. In this case the transmitters radiate the waves in opposite phases. The wall of cylinder for point- form source is similar to infinite plate. It allows us to use the beam model for simulating. But the beams in the space have a helical form. A receiving point is placed on a line, paralel to the cylinder axle, where one transmitter lies. The wave at the receiving point is the superposition of the first wave, coming by shortest way, and the other, each passing one rotation more. Such system of coherent waves interferes, and this is a reason of signal oscillations. The covering curve has no oscillations only in two cases: the receiving point lies exactly opposite to transmitter or at the great distance from it. Some transient covering curves were calculated, registered experimentally and discussed. The dependence of transient process on the exciting geometry and amplitude ratio of both partial waves may be used for NDT of pipes. On the other hand it is possible to use the calculated transient response as a reaction of the wave-guide to the some kind of "step function" by investigating the processes with more complicated excitation. References 8. Figures 4.