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1
Content available Application of the scattering matrix method to evaluate acoustic mufflers properties
Gorazd Łukasz
Vibrations in Physical Systems
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2022
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Vol. 33, nr 2
art. no. 2022204
EN
The aim of the paper is to analyse acoustic reflective muffler applying the scattering matrix method. In general, the method is based on dividing the muffler/system into separate subsystems and apply the acoustic multi-ports theory to calculate the scattering matrix of each element to finally combine the results and obtain the scattering matrix of the entire system/muffler. The multi-port procedure is derived from the theory of electric networks and allows to analyse acoustic devises of complex geometry with prescribed accuracy. Based on the scattering matrix, the transmission loss was determined.
2
Content available Experimental Determination of a Reflective Muffler Scattering Matrix for Single-Mode Excitation
Gorazd Łukasz
Archives of Acoustics
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2021
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Vol. 46, No. 4
667--675
EN
The aim of the paper is to experimentally determine the scattering matrix S of an example reflective muffler of cylindrical geometry for Helmholtz number exceeding the plane wave propagation. Determining the scattering matrix of an acoustic systems is a new and increasingly used approach in the assessment of reduction of noise propagating inside duct-like elements of heating, ventilation and air conditioning systems (HVAC). The scattering matrix of an acoustic system provides all necessary information on the propagation of wave through it. In case of the analysed reflective silencer, considered as a two-port system, the noise reduction was determined by calculating the transmission loss parameter (TL) based on the scattering matrix (S). Measurements were carried out in two planes of the cross-section of pipes connected to the muffler. The paper presents results of the scattering matrix evaluation for the wave composed of the plane wave (mode (0,0)) and the first radial mode (0,1), each of which was generated separately using the self-designed and constructed single-mode generator. The gain of proceeding measurements for single modes stems from the fact that theoretically, calculation of the S-matrix does not require, as will be presented in the paper, calculation of the measurement data inverse matrix. Moreover, if single mode sound fields are well determined, it ensures error minimization. The presented measurement results refer to an example of a duct like system with a reflective muffler for which the scattering matrix S was determined. The acoustic phenomena inside such a system can be scaled by the parameter ka.
3
Content available Simulation of a single mode wave generation in cylindrical systems applying numerical methods
Gorazd Łukasz, Snakowska Anna
Vibrations in Physical Systems
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2019
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Vol. 30, nr 1
art. no. 2019118
EN
The paper presents simulations of a selected single mode generation in systems containing duct-like elements applying the finite element method (FEM). Simulations were carried out for values of the Helmholtz number exceeding the plane-wave propagation, i.e. for a multimode wave. The presented results constitute the first step to analyse propagation of the multimode wave through more complicated systems such as mufflers, even in a form of a cascade. Propagation of the incident wave in the form of a single mode greatly simplifies solutions of many problems, to mention only derivation of the transmission or the scattering matrices. The results obtained can be applied to analyse the effectiveness of attenuation of acoustic silencers or elements of heating, ventilation and air conditioning systems (HVAC) at the design stage. Results of simulations are compared with already published experimental data obtained in a measurement set-up containing the self-designed single mode synthesizer.
4
Content available 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.
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