چكيده به لاتين
In this thesis, sound transmission from two-layered cylindrical shells containing viscous fluid has been studied analytically. For this purpose, it is assumed that a two-layered cylindrical shell containing a viscous fluid of unlimited length is exposed to a moving uniform flow and immersed in an ideal fluid and is subjected to the radiation of an inclined plane sound wave, as a result of which, the reflection and transmission of the wave Is achieved.In the first step, to extract the structural movement equations, the stress, strain and displacement equations are first written through the three-dimensional theory of elasticity. In the next step, with the help of Newton's second law, the equilibrium equations governing a small element of the cylinder are implemented in three dimensions. Through the equilibrium equations, the equation of motion governing the cylinder is derived. With the help of Helmholtz decomposition, the motion equation can be decomposed into two separate wave equations and the displacement field can be obtained by solving each of these equations separately. In the following, using the Neuer-Stokes equations, the equations governing the viscous fluid are obtained. Also, the equations of the corresponding acoustic vibrations in all three axial, peripheral and radial directions are established by applying appropriate boundary conditions, displacement field and pressure based on infinite series. For the acoustic solution, a powerful analysis of the transfer matrix method was used. Finally, in order to investigate a suitable design, a very famous parameter called sound transmission loss coefficient (TL) has been used. Since the pressure and displacement fields are infinite series and considering the fact that sufficient number of modes should be used in the analysis, a suitable algorithm is used to check the convergence. Finally, the important physical and geometrical parameters affecting the sound transmission loss of the structure, such as viscous fluid type, shell radius, shell thickness, sound wave impact angle, Mach number, shell material, etc., have been discussed and investigated.
