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Effect of geometry and impedance variation on the acoustic performance of a porous material lined duct

Masmoudi A., Makni A., Taktak M., Haddar M.

Journal of Theoretical and Applied Mechanics

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2017

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Vol. 55 nr 2

679--694

EN

In this paper, the effect of geometry and impedance on the acoustic behavior of wall and lined cylindrical ducts is investigated using a numerical model which enables one to compute the reflection and the transmission coefficients of such ducts using the multimodal scattering matrix. From this matrix, the acoustic power attenuation is deduced. By using these tools, the effect of duct diameter increase and duct diameter decrease of the wall or lined duct section is studied. The numerical results are obtained for two configurations of wall and lined ducts. Numerical coefficients of transmission and reflection as well as the acoustic power attenuation show the relative influence of each type of variation.

2

Numerical analysis of pressure drop and acoustic attenuation performance of two helicoidal resonators arranged in parallel ducts with different rotation angles

Łapka W.

Vibrations in Physical Systems

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2016

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Vol. 27

237--244

EN

The paper presents a numerical analysis of pressure drop and acoustic attenuation performance (transmission loss) of two identical acoustic helicoidal resonators arranged in parallel ducts with different rotation angles. The air stream is divided from one cylindrical duct of a diameter D=140mm to a two parallel cylindrical ducts of diameter d=125mm with two helicoidal resonators inside – one per one duct. The ratio of helicoidal pitch s of helicoidal resonators to a cylindrical duct diameter d equals s/d=1,976. Other geometrical relationships of helicoidal resonators, as a mandrel diameter dm to duct diameter ratio dm/d=0.024, thickness g of helicoidal profile g/d=0.0024, and the number of helicoidal turn n=0,695 for both resonators. The investigated range of rotation angles covered the three characteristic positions of helicoidal resonators gaps, when considering the air stream distribution from central large duct with diameter D. The value of normal inflow velocity v[m/s] equaled 1 for all investigated cases.

3

Effect of Liner Characteristics on the Acoustic Performance of Duct Systems

Othmani C., Hentati T., Taktak M., Elnady T., Fakhfakh T., Haddar M.

Archives of Acoustics

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2015

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Vol. 40, No. 1

117--127

EN

Porous materials are used in many vibro-acoustic applications. Different models describe their performance according to material’s intrinsic characteristics. In this paper, an evaluation of the effect of the porous and geometrical parameters of a liner on the acoustic power attenuation of an axisymmetric lined duct was performed using multimodal scattering matrix. The studied liner is composed by a porous material covered by a perforated plate. Empirical and phenomenal models are used to calculate the acoustic impedance of the studied liner. The later is used as an input to evaluate the duct attenuation. By varying the values of each parameter, its influence is observed, discussed and deduced.

4

Design, Manufacture and Characterization of an Acoustic Barrier Made of Multi-Phenomena Cylindrical Scatterers Arranged in a Fractal-Based Geometry

Casteneira-Ibanez S., Rubio C., Romero-Garcia V., Sanchez-Perez J. V., Garcia-Raffi L. M.

Archives of Acoustics

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2012

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Vol. 37, No. 4

455-462

EN

In this work we present the design and the manufacturing processes, as well as the acoustics standard- ization tests, of an acoustic barrier formed by a set of multi-phenomena cylindrical scatterers. Periodic arrangements of acoustic scatterers embedded in a fluid medium with different physical properties are usually called Sonic Crystals. The multiple scattering of waves inside these structures leads to attenuation bands related to the periodicity of the structure by means of Bragg scattering. In order to design the acoustic barrier, two strategies have been used: First, the arrangement of scatterers is based on fractal geometries to maximize the Bragg scattering; second, multi-phenomena scatterers with several noise con- trol mechanisms, as resonances or absorption, are designed and used to construct the periodic array. The acoustic barrier reported in this work provides a high technological solution in the field of noise control.