چكيده به لاتين
In this thesis, sound transmission through a multilayered cylindrical shell consists of
an outer functionally graded shell, a functionally graded poroelastic core, an airgap,
and an inner isotropic shell is investigated. The material properities of the core is
considered to have a gradiant variation along the thickness of the layer with a powerlaw distribution. The core is assumed to be made up of finite number of
homogeneous proselastic sublayers, and the extended full method is used to describe
the displacement and stress fields of each sublayer. Contrary to previous methods,
this method brings about more precision and also, three-dimensional analysis of the
poroelastic material considereing airbourne, frame, and shear waves in the medium.
Next, the filed variables of inner and outer surfaces of each sublayer is connected by
a local transfer matrix, therefore, by writing these matrices for adjacent layers, a
global transfer matrix is achieved which relates the desplacements and stress
components of the inner and outer surfaces of the cylindrical core. Moreover, the
inner and outer shells of the multilayered structure is modeled via the first-order
shear deformation theory. Finally, by the use of boundary conditions, the sound
transmission loss of the structure is calculated. The results show that the presence of
a functionally graded poroelastic core improves the sound absorbtion of the structure.
