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Generalized Transfer Matrix Method for periodic planar media
Full text linkSound transmission through infinite planar multilayered structures characterized by in-plane periodicity is accurately and efficiently predicted by exploiting free wave propagation and Bloch modes. A through-thickness transfer matrix is derived for each layer by manipulating the dynamic stiffness matrix related to a finite element model of a unit cell. The transfer matrices of all the layers composing the structure account for the Bloch modes generated in heterogeneous layers. The proposed technique is equally appealing for in-plane homogeneous structures since few elements and no Bloch modes are needed in this case, ensuring high efficiency. In such a framework, the acoustic radiation or transmission of multilayered systems excited by an oblique plane wave can be assessed. The proposed approach is validated in case of structures consisting of heterogeneous layers by comparison with alternative approaches
Modal density of rectangular structures in a wide frequency range
Full text linkA novel approach to investigate the modal density of a rectangular structure in a wide frequency range is presented. First, the modal density is derived, in the whole frequency range of interest, on the basis of sound transmission through the infinite counterpart of the structure; then, it is corrected by means of the low-frequency modal behavior of the structure, taking into account actual size and boundary conditions. A statistical analysis reveals the connection between the modal density of the structure and the transmission of sound through its thickness. A transfer matrix approach is used to compute the required acoustic parameters, making it possible to deal with structures having arbitrary stratifications of different layers. A finite element method is applied on coarse grids to derive the first few eigenfrequencies required to correct the modal density. Both the transfer matrix approach and the coarse grids involved in the finite element analysis grant high efficiency. Comparison with alternative formulations demonstrates the effectiveness of the proposed methodology
Evaluation of damping loss factor of flat laminates by sound transmission
Full text linkA novel approach to investigate and evaluate the damping loss factor of a planar multilayered structure is presented. A statistical analysis reveals the connection between the damping properties of the structure and the transmission of sound through the thickness of its laterally infinite counterpart. The obtained expression for the panel loss factor involves all the derivatives of the transmission and reflection coefficients of the layered structure with respect each layer damping. The properties of the fluid for which the sound transmission is evaluated are chosen to fulfil the hypotheses on the basis of the statistical formulation. A transfer matrix approach is used to compute the required transmission and reflection coefficients, making it possible to deal with structures having arbitrary stratifications of different layers and also granting high efficiency in a wide frequency range. Comparison with alternative formulations and measurements demonstrates the effectiveness of the proposedmethodology
Diffuse field transmission through multilayered cylinders using a Transfer Matrix Method
Full text linkThis paper discusses the use of a Transfer Matrix (TM) method for predicting the acoustic behavior of infinite cylinders consisting of a generic arrangement of homogeneous and heterogeneous periodic layers of various nature (fluid, solid, poroelastic). A through-radius TM is derived for a layer characterized by cylindrical periodicity by manipulating the dynamic stiffness matrix related to a finite element model of a unit cell. The proposed technique is equally appealing for homogeneous layers since few elements are needed in this case. In such a framework, different layers can be combined to form multilayered systems and the related acoustic radiation or transmission due to an external plane wave or a diffuse acoustic field can be assessed. The proposed approach is validated in case of cylinders consisting of homogeneous layers by comparison with alternative approaches. In order to demonstrate the usefulness of the approach, the sound transmission through a cylindrical structure with resonators is presented
Development of an innovative configuration for transport aircraft; a project of five Italian universities
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