Magliacano, Dario (2020) Vibroacoustics of Porous Media with Periodic Inclusions. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Resource language: English
Title: Vibroacoustics of Porous Media with Periodic Inclusions
Date: 20 February 2020
Number of Pages: 161
Institution: Università degli Studi di Napoli Federico II
Department: Ingegneria Industriale
Dottorato: Ingegneria industriale
Ciclo di dottorato: 32
Coordinatore del Corso di dottorato:
Khelif, AbdelkrimUNSPECIFIED
Franco, FrancescoUNSPECIFIED
Date: 20 February 2020
Number of Pages: 161
Keywords: vibroacoustics; porous; periodic; dispersion; absorption; transmission; shift cell; branch tracking
Settori scientifico-disciplinari del MIUR: Area 09 - Ingegneria industriale e dell'informazione > ING-IND/04 - Costruzioni e strutture aerospaziali
Date Deposited: 07 Feb 2020 14:45
Last Modified: 17 Nov 2021 10:49

Collection description

The design based on periodic elements is a powerful strategy for the achievement of lightweight sound packages and represents a convenient solution for manufacturing aspects. Several theoretical models exist to study the physical behavior of porous and poro-elastic media, and the most complex ones are based on the definition of more than ten parameters. For example, the theory of poro-elasticity formulated by Maurice Biot allows to take into account the mechanical properties of the foam, simultaneously to its acoustical characteristics. In addition, some of these parameters are very complicated to measure; therefore, while the estimation of all the necessary parameters usually represents the starting point in the construction of a reliable model, in this case it constitutes by itself a specific difficulty. This is one of the reasons why, although poro-elastic media are extensively used for several industrial applications in order to fulfill strictly-regulated requirements of noise reduction, their modeling still represents a non-trivial issue. Numerical simulation techniques, like Finite Element Methods (FEM), may be problematic in case of real complex geometries, especially in terms of computational times and mesh convergence. On the other hand, analytical models, although being partially limited by approximating assumption, constitute a powerful tool to quickly understand physics and general trends of the problem. Even if porous and poro-elastic media are widely used for vibroacoustic applications, they suffer from a lack of performances at low frequencies compared to their efficiency at higher ones. This issue is generally overcome by multi-layering; anyway, the efficiency of such systems depends on the allowable thickness. A more efficient technique to improve the low frequency performances of sound packages consists in including a periodic pattern in a foam, in order to create wave interferences or resonance effects that may be advantageous for the system dynamics. In this context, numerical tools to properly design sound packages are more and more studied. An interesting research target is the inclusion of vibroacoustic treatments at early stage of product development through the use of porous media with periodic inclusions, which exhibit proper dynamic filtering effects; this addresses different applications in transportation (aerospace, automotive, railway), energy and civil engineering sectors, where both weight and space, as well as vibroacoustic comfort, still remain as critical issues. The main numerical tool that is developed in this work is the shift cell operator approach, which allows the description of the propagation of all existing waves from the definition of the unit cell, through the resolution of a quadratic eigenvalue problem that can handle any frequency-dependent parameters. It belongs to the class of the k(ω) (wave number as a function of the angular frequency) techniques, instead of using the classical ω(k) (angular frequency as a function of wave number) that leads to non-linear eigenvalue problems. This method has been already successfully used for the description of the mechanical behavior of periodic visco-elastic or piezoelectric structures. Here it is proposed an extension to equivalent fluid and diphasic models of porous materials, which makes possible to overcome the limits of existing approaches in order to obtain a device whose frequency efficiency outperforms existing designs. The aim of this manuscript, therefore, is to introduce some enhancements to the state of the art of the shift cell approach applied to equivalent fluid and diphasic models embedding a periodic pattern.


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