Acoustic Investigation On Functionally Graded Material's Plate And Shell Structures

Functionally graded material (FGM) is special nonhomogeneous material. And it was first introduced by Japanese scientists in 1984. Since then, FGM has received more and more attention. Nowadays, FGM has extended their first applications in aerospace to electronics, chemistry, optics, biomedicine, acoustics, nuclear engineering, civil engineering, mechanical engineering (auto-engine, brake and wheel of bullet train) and the like. Research on the behavior of FGM structures acoustic problen not only benefits the needs of acoustic theory, but also satisfies the needs of practice.First, the models of radiated sound of baffled functionally graded material rectangular plate and infinite length plate strip are set up and investigated theoretically in this dissertation. By basic dynamic equation of FGM rectangular plate, the flexural displacement is obtained by modal analysis method that they are excited by various excitation forces. And using Fourier transform and Rayleigh's formula, a far-field approximation solution of the radiated sound field is derived in a closed form. And the near acoustic field is investigated by a numerical integral method.Second, the sound radiation model of a finite FGM cylindrical shell driven by a harmonious point force with the outer shell coated with compliant layer is set up, and the vibroacoustic characteristics of different FGM shell's and damping layer's parameters are systematically studied. The acoustic pressure expression is attained by the FGM shell's dynamic equation, the Helmholtz equation, the boundary conditions of the FGM shell surface and the Fourier integral transform of finite shell, where the layer motion is described by means of the three-dimensional Navier equations. Lastly, through the boundary conditions of the damping layer combined with the shell the coupled oscillation equation was solve, and radiation sound field expression was shown using the shell displacements. In the end, the parameters of the acoustic radiated power level and the radial quadratic velocity level are calculated. And these two parameters indicate the general characteristics of the FGM shell vibration and sound radiation.Third, a theoretical model is developed to evaluate the vibration and sound radiation of a FGM cylindrical shell excited by a constant point load continuously traveling along the circumferential direction at a rotational speedΩ, and the FGM shell is immersed in two different fluids of air and water. The present approach is based rather on a frequency-domain solution of the vibratory and acoustic responses of the FGM shell, and such a frequency-domain solution is convenient to interpret the vibratory and acoustic responses in terms of shell modes.Finally, the sound scattering by functionally graded material cylindrical shell is investigated in this dissertation. The original inhomogeneous shell with the material parameters's change along the thickness is approximated by a laminate modal. So the FGM shell is turned into a cylindrical layered structure with transversely isotropic symmetry. The transfer matrix solution is expected to gradually involves a system global transfer matrix formed as the product of the individual transfer matrices by applying continuity of the displacement and stress components at the interfaces of neighbouring layers, is employed to solve for the scattering coefficients.We find that geometric parameters, material paratemers and power law index of the plate and shell affect the responses of FGM structures's vibroacoustic behaviour. This dissertation hopes to bring some insights on the acoustic designing of the FGM structures.