Structural-acoustic studies of sandwich structures for global transport aircraft

The optimization of sandwich structures with high strength and light weight have been the topic of interest for many researchers. There have also been a few studies on the vibration and sound transmission across these structures. This dissertation presents the structural and acoustic studies of sandwich structures for global transport aircraft applications.; One of the objectives of this research is to introduce certain material anisotropy in the layers of the sandwich which will enhance the vibration and sound transmission characteristics of the structure. To illustrate this research concept, the sound transmission loss across an anisotropic sandwich beam has been studied in detail using a higher-order model of the sandwich beam. It is observed that there is a significant increase in the transmission loss for the sandwich beam with anisotropic materials as compared with isotropic ones. A study on the optimization of sound transmission loss across the anisotropic sandwich beam is also presented. This work lays the basic foundation for material scientists to design new sandwich structures with high vibration and noise isolation performance.; The second part of the dissertation deals with the structural and the acoustic analyses of a non-circular, cylindrical, laminated, anisotropic shell. The shell has a cross-section consisting of a square with rounded corners. The method of conformal mapping is employed to map the physical domain onto a circular cylindrical domain. The Rayleigh-Ritz method is then used in conjunction with Hamilton's principle in order to obtain the final solution in both the analyses.; The analysis of fully coupled structural-acoustic systems is presented in the next chapter. A method for the analysis of such coupled systems is developed using a particular solution approach. A simple two dimensional rectangular cavity is used as an example to illustrate the solution approach in detail. The method is also applied to a three-dimensional system: the non-circular cylindrical shell mentioned earlier. The Galerkin and the Rayleigh-Ritz methods are used to obtain the coupled modal equations for the system which are solved using a state space formulation. Numerical results are presented which show the mode shapes of the coupled systems.