چكيده به لاتين
This Thesis focuses on the acoustic characteristic of a simply supported doubly curved composite shell subjected to the Pasternak-type elastic foundation and doubly curved sandwich shell with poroelastic core subjected to the Pasternak-type elastic foundation. To analyze the sound performance of a finite curved shell, displacements and rotation terms and acoustic pressures are formed in terms of the double Fourier series as a function of infinite longitudinal and transversal modes. Hamilton’s principle is applied to present the differential equations of motion equipped with elastic foundation considering shear deformation shallow shell theory (SDSST). Subsequently, the construction is stimulated using an acoustic wave in the mean flow. Considering infinite modes, the necessity of terminating this process by applying a large number of modes is concerned. Accordingly, to present the reliable outcomes, in addition to the design of the convergence algorithm, a series of 3D configurations against variations of dimensions and frequencies are proposed. Before presenting the numerical outcomes, the formulation's accuracy is checked by either natural frequencies or sound transmission spectra. These validations confirm the accuracy of the findings due to applicable agreements in both free vibration analyses and noise performance curves. As another consequence, in the following, the effect of using a two-parameter elastic foundation through the noise insulation is inspected. It is realized that although Winkler spring stiffness is impressive to improve the noise property at the low-frequency domain, the positive effects of Shear layer one are specified in the whole frequency domain. The outcomes also contain some 3D new shapes for variations of the Winkler spring and Shear layer stiffness.
