P5E-5 On the Propagation in a Waveguide with Gaussian Section Variation: Inverse Problem to Determine the Hiding Waveguide Profile and Separation of Converted Modes Contributions in the Case of Multi-Incident Modes, Experimental and Numerical Studies

In previous work [1] on propagating waves in a plane elastic waveguide containing an area of Gaussian section variation (GSV) located between two areas of constant thickness, we have shown experimentally and numerically the existence of adiabatic modes inside the area of GSV as well as Lamb modes conversion. The aim of this paper is to exploit these results into two directions: 1) The determination of the waveguide profile from the experimental and numerical results, 2) In the case when two Lamb modes are simultaneously incident on the GSV, the separation of their contributions on the converted Lamb modes transmitted outside the GSV. The adiabatic behaviour of the incident Lamb wave inside the area of GSV allows an inverse problem method to determine the hiding Gaussian profile of the waveguide. The local wavenumber inside the area of GSV is nearly the same than in a plate of constant thickness. These local wavenumber values are then compared to the theoretical ones obtained from the dispersion equation solutions of the considered Lamb mode. As these solutions are given as function of the frequency-thickness product, the local thickness is then deduced, as the frequency of analysis is given. On an other hand, several Lamb modes are often simultaneously experimentally generated, because of the contact transducer limiting size and the multireflections of the incident beam inside the wedge. A method, based on space-time FFT is achieved to determine the contribution of each incident Lamb mode on the transmitted ones outside the area of GSV.