The Modal Transformation Study Of Lamb Wave On The Plate End

The underwater target is usually the elastic shell,and the scattering wave generated by the incoming acoustic excitation will have elastic scattering wave,which is the elastic wave in the elastic shell.The elastic waves in elastic plates are propagated by the Lamb wave with different modes of vibration mode,while the Lamb wave is reflected in the panel and the modal transformation occurs.Studying the modal transformation of Lamb wave on the plate is the basis of the analysis of the spatial distribution of the scattering sound field of the underwater elastic plate,which is of practical significance to the identification and detection of the separation sonar target.Paper by elastomer of wave equation and the boundary conditions of different circumstances,vacuum was deduced respectively and underwater Lamb wave dispersion equation of the elastic plate,using " The dichotomy" and "Enclosure Division" numerical integral method is used to solve the corresponding conditions of Lamb wave phase velocity,group velocity and attenuation coefficient of dispersion curve;The dispersion curves of Lamb waves in three different elastic plates are compared.This paper provides a basis for identifying the leakage wave of the corresponding mode in the elastic plate scattering wave field.Based on the analysis of modal orthogonal theory,the conversion efficiency of low-order Lamb on the plate end of the elastic plate of different end-face plates is calculated.Using the finite element sound field calculation software COMSOL,the scattering sound field of the elastic plate under the surface wave is calculated by numerical calculation.In this paper,the scattering sound field is decomposed and the space Angle spectrum of the scattering wave field is obtained.And leaky wave propagation direction depends on the elastic wave 'critical Angle,because each order Lamb wave velocity in the elastic plate is different,the corresponding critical Angle is different,so the spectrum can be obtained by scattering wave field space Angle corresponding mode of Lamb wave leaky wave intensity.Combined with the conservation of energy law,the efficiency of the modal conversion of Lamb waves in the plate is calculated by ignoring the dispersion wave(such as angular wave).Underwater elastic scattering sound field numerical calculation results show that:(1)only to a certain mode of Lamb wave incident sound waves the critical Angle of the incident to the elastic plate surface,can inspire a corresponding modal in the plate to Lamb wave.(2)there are multiple modes of the reverse Lamb wave after the reflection of the plate side in a mode,which is the modal transformation phenomenon.(3)the symmetric mode of Lamb in the underwater elastic plate is affected by the non-existence of energy exchange between the modal Lamb waves.(4)according to the simulation experimental data,the modal transformation efficiency is estimated by using the calculation method in this paper.the simulation experimental value is consistent with the theoretical value.