Study On Leaky Lamb Waves Propagation In Elastic Plates And Cylindrical Shells Coated With A Viscoelastic Damping Material In Water

Underwater anechoic coating is a key technology to the realization of acoustic stealth. The study of target echo of elastic shells coated with viscoelastic damping layers is significant to sonar target detection and identification. The target echoes are mainly consisted of mirror reflecting echoes, elastic scattering echoes and edge and corner echoes. The formation mechanism of elastic scattering echo is closely related to sound propagation along elastic targets'surface.Propagation problems of Lamb waves in elastic plates and elastic plates coated with viscoelastic damping layers, and Lamb-like waves in cylindrical shells and cylindrical shells coated with viscoelastic damping layers are studied in this paper. The dispersion equations of Lamb waves under three different boundary conditions such as free, one side free one side water loading and water loading are derived and solved by numerical methods. Dispersion curves and attenuation curves are obtained. The numerical methods of dispersion equation, including bisection method, winding number integration method, Muller method and local peaks search method, are investigated and validated. Target echo experiment of elastic plates, elastic plates coated with viscoelastic damping layers and cylindrical shells is done. Through degree-time pseudo-color graphs of target echo signals, the structure of target echoes is analyzed. It is validated that the formation mechanism of elastic scattering echoes of elastic plates and cylindrical shells can be explained by theory of Lamb waves.