Wyniki wyszukiwania - Biblioteka Nauki

1

Identification of Physical Parameters of a Porous Material Located in a Duct by Inverse Methods

100%

Kani M. , Makni A. , Taktak M. , Chaabane M. , Haddar M.

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2021

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tom Vol. 46, No. 4

657--665

EN

Lined ducts with porous materials are found in many industrial applications. To understand and simulate the acoustic behaviour of these kinds of materials, their intrinsic physical parameters must be identified. Recent studies have shown the reliability of the inverse approach for the determination of these parameters. Therefore, in the present paper, two inverse techniques are proposed: the first is the multilevel identification method based on the simplex optimisation algorithm and the second one is based on the genetic algorithm. These methods are used of the physical parameters of a simulated case of a porous material located in a duct by the computation of its acoustic transfer, scattering, and power attenuation. The results obtained by these methods are compared and discussed to choose the more efficient one.

2

Investigation on the Effects of Acoustic Liner Variation and Geometry Discontinuities on the Acoustic Performance of Lined Ducts

100%

Dhief R. , Makni A. , Taktak M. , Chaabane M. , Haddar M.

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2020

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tom Vol. 45, No. 1

49--66

EN

Noise reduction inside waveguide systems has gained momentum owing to a great interest in it. To attenuate the sound in a broad frequency range, this study aims to compare the effects of two acoustic liners, a perforated plate backed by an air cavity (PP-Air cavity), or by a porous material (PP-PM), on the acoustic behaviour of lined ducts using a numerical model to compute the multimodal scattering matrix. From this matrix, the reflection and the transmission coefficients are computed and therefore the acoustic power attenuation is deduced. Moreover, the effects of geometry of ducts with and without changes in the section are investigated. The numerical results are obtained for five configurations, including cases of narrowing and widening of a duct portion with sudden or progressive discontinuities. Accordingly, numerical coefficients of reflection and transmission as well as the acoustic power attenuation show the relative influence of acoustic liners in each type of configuration.

3

Numerical characterization of an axisymmetric lined duct with flow using the multimodal scattering matrix

100%

Taktak M. , Majdoub M. A. , Haddar M. , Bentahar M.

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2013

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tom Vol. 51 nr 2

313--325

EN

In this paper, the development of a numerical method to compute the multimodal scattering matrix of a lined duct in the presence of flow is presented. This method is based on the use of the convected Helmholtz equation and the addition of modal pressures at duct boundaries as additional degrees of freedom of the system. The boundary effects at the inlet and outlet of the finite waveguide are neglected. The choice of this matrix is justified by the fact that it represents an intrinsic characterization of a duct system. The validation of the proposed finite element is done by a comparison with the analytical formulation for simple cases of ducts. Then, the numerical coefficients of the scattering matrix of a lined duct and its acoustic power attenuation are computed for several flow velocities to evaluate the flow effect.

PL

W pracy zaprezentowano numeryczną metodę wyznaczania macierzy rozpraszania dla wyściełanego przewodu z uwzględnieniem wewnętrznego przepływu czynnika. Metodę oparto na zastosowaniu równania konwekcji Helmholtza z wprowadzeniem ciśnień modalnych na brzegach jako dodatkowych stopni swobody układu. Efekty brzegowe na wlocie i wylocie przewodu falowego o skończonej długości pominięto. Wybór macierzy rozpraszania uzasadniono faktem, że reprezentuje ona wewnętrzną charakterystykę analizowanego modelu. Zaproponowany element skończony zweryfikowano poprzez porównanie z istniejącymi rozwiązaniami analitycznymi dla prostych przypadków konfiguracji przewodu. Następnie numerycznie obliczono wartości elementów macierzy rozpraszania oraz współczynniki tłumienia akustycznego dla kilku prędkości przepływu w celu określenia, jak dalece wpływa on na badany układ.

4

On the S-matrix of Schrodinger operator with nonlocal 6-interaction

88%

Główczyk A. , Kużel S.

Opuscula Mathematica

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2021

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tom Vol. 41, no. 3

413--435

EN

Schrodinger operators with nonlocal δ-interaction are studied with the use of the Lax-Phillips scattering theory methods. The condition of applicability of the Lax-Phillips approach in terms of non-cyclic functions is established. Two formulas for the S-matrix are obtained. The first one deals with the Krein-Naimark resolvent formula and the Weyl-Titchmarsh function, whereas the second one is based on modified reflection and transmission coefficients. The S-matrix S(z) is analytical in the lower half-plane C- when the Schrodinger operator with nonlocal δ-interaction is positive self-adjoint. Otherwise, S(z) is a meromorphic matrix-valued function in C- and its properties are closely related to the properties of the corresponding Schrodinger operator. Examples of S-matrices are given.

5

Scattering matrices of multiport radio devices

88%

Czawka G.

Przegląd Elektrotechniczny

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2016

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tom R. 92, nr 2

18--22

EN

This paper deals with the mathematics models and properties of three types the scattering matrices for arbitrary multiport devices normalized to separate resistive loads, separate complex loads and complex n-port load. The introduced scattering matrices describe a matching problem in different multiport structures, for example a connection of given antenna array with multiport beamformer. These mathematics models may be used for analysis of signal distribution and their disturbances in different multiport structures and for the design of any optimum multiport devices.

PL

Artykuł przedstawia modele matematyczne i właściwości trzech typów macierzy rozproszenia dla dowolnych układów wielowrotnikowych normalizowanych do osobnych rezystywnych i zespolonych obciążeń oraz do obciążenia wielowrotnikowego. Wprowadzone macierze opisują problem dopasowania różnorodnych wielowrotnikowych struktur.

6

Experimental Determination of a Reflective Muffler Scattering Matrix for Single-Mode Excitation

88%

Gorazd Ł.

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2021

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tom 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.

7

Effect of Liner Characteristics on the Acoustic Performance of Duct Systems

88%

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

Archives of Acoustics

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2015

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tom 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.

8

Technical Note. Effect of Liner Characteristics on the Acoustic Performance of Duct Systems

75%

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

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2015

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tom 40

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nr 1

9

Analysis of power parameters of two-port antenna using a new scattering matrix

75%

Czawka G. , Garbaruk M.

Przegląd Elektrotechniczny

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2016

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tom R. 92, nr 2

14--17

EN

The paper presents results of a computer simulation of the power parameters’ characteristics of a two-port antenna with the use of a new scattering matrix normalized to a complex impedance matrix of coupled generators. It is shown that there is an infinite number of the scattering matrices for the given two-port complex load (or the network of generators) and all of these describe the same power distribution in the given networks.

PL

Artykuł przedstawia wyniki symulacji komputerowej charakterystyk parametrów energetycznych dwuwrotnikowej anteny z zastosowaniem nowej macierzy rozproszenia normalizowanej do pełnej macierzy impedancji generatorów. Pokazano, że istnieje nieskończona ilość takich macierzy rozproszenia dla danego dwuwrotnikowego obciążenia (lub macierzy impedancji generatorów), określających ten sam rozkład mocy w danym układzie.

10

Scattering of internal waves by vertical barrier in a channel of stratified fluid

63%

Dolai P.

International Journal of Applied Mechanics and Engineering

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2015

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tom Vol. 20, no. 3

471--485

EN

The problem of two dimensional internal wave scattering by a vertical barrier in the form of a submerged plate, or a thin wall with a gap in an exponentially stratified fluid of uniform finite depth bounded by a rigid plane at the top, is considered in this paper. Assuming linear theory and the Boussinesq approximation, the problem is formulated in terms of the stream function. In the regions of the two sides of the vertical barrier, the scattered stream function is represented by appropriate eigen function expansions. By the use of appropriate conditions on the barrier and the gap, a dual series relation involving the unknown elements of the scattering matrix is produced. By defining a function with these unknown elements as its Fourier sine expansion series, it is found that this function satisfies a Carleman type integral equation on the barrier whose solution is immediate. The elements of the scattering matrix are then obtained analytically as well as numerically corresponding to any mode of the incident internal wave train for each barrier configuration. A comparison with earlier results available in the literature shows good agreement. To visualize the effect of the barrier on the fluid motion, the stream lines for an incident internal wave train at the lowest mode are plotted.

11

Istota i ewolucja struktur organizacyjnych na potrzeby logistyki w sądownictwie powszechnym

63%

Odlanicka-Poczobutt M.

Logistyka

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2013

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tom nr 6

39--41

PL

W artykule przedstawiono istotę organizacji logistyki i struktur organizacyjnych na potrzeby logistyki w szczególnym typie organizacji, jaką jest sądownictwo powszechne. Z uwagi na rozpiętość zagadnienia artykuł stanowi jedynie fragment szerszych rozważań zawartych w innych publikacjach autorki. W artykule zaprezentowano macierz rozproszenia zadań logistycznych w organizacji ze względu na stopień centralizacji oraz wskazano sugerowane zorientowanie struktur ze względu na specyfikę badanego podmiotu. Całość zakończono wnioskami.

EN

The paper presents the essence of the organization of logistics and organizational structures for the logistics in a particular type of organization, which is the common judiciary. Given the breadth of issues article is only part of the broader considerations in other publications of the author. The article presents the scattering matrix of logistics tasks in the organization because of the degree of centralization and indicates the orientation of the structures suggested due to the nature of the test subject. The whole was completed by conclusions.

12

Application of the scattering matrix method to evaluate acoustic mufflers properties

63%

Gorazd Ł.

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tom 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.

13

Projektowanie mikrofalowych wzmacniaczy małoszumnych

51%

Kral J.

Elektrotechnika i Elektronika

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2000

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tom T. 19, z. 1

60--74

PL

W pracy przedstawiono sposób projektowania małoszumnego wzmacniacza mikrofalowego z elementami o stałych rozłożonych. Podano zależności projektowe, na podstawie których można przeprowadzić analizę graficzną układu. Omówiono ograniczenia wynikające z potencjalnej niestabilności tranzystora oraz kompromisu pomiędzy minimalnym współczynnikiem szumów a maksymalnym wzmocnieniem mocy. Podano syntetyczny algorytm projektowania. Przedstawiono też przykład projektowania wzmacniacza na 5 GHz o minimalnym współczynniku szumów rzędu 1 dB i wzmocnieniu mocy około 12 dB. Zaprezentowano sposób zwiększenia marginesu stabilności oraz szczegółowy sposób zaprojektowania obwodów dopasowujących. Pokazano też fizyczną realizację wzmacniacza (layout) na podłożu laminowanym w technice niesymetrycznych linii paskowych.

EN

This article covers the design of a low noise amplifier with distributed matching elements. Basic design relations which serve to graphical analysis are provided. Limitations connected with transistor stability and compromise between noise figure and power gain are discussed. Design procedure is formulated for a potentially unstable transistor. As an example there is a design of the amplifier with a GaAs MESFET with a noise figure of 1 dB and 12 dB gain around 5 GHz. The technique of increasing stability region and detailed matching circuit design are shown. Analysis and optimisation results are included. Presentation of amplifier layout on laminate substrate in microstrip technology closes the paper.

14

Wykorzystanie wartości własnych macierzy impedancji falowych do wyznaczania parametrów cyrkulatorów ferrytowych

51%

Sędek E.

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2020

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tom Vol. 61, nr 10

27--30

PL

Metoda przedstawiona poniżej została opracowana dla cyrkulatorów paskowych i mikropaskowych z wielostopniowymi transformatorami dopasowującymi, przy czym transformator może zawierać czwórniki mikrofalowe zbudowane z liniowych elementów biernych. W stosowanych dotychczas metodach projektowania cyrkulatorów transformator dopasowujący był uwzględniany dla warunków brzegowych dla składowych stycznych pól E i H na kolejnych nieciągłościach ferryt-dielektryk, dielektryk-dielektryk itd.[2]. Stosowano również metodę obliczeń, opartą na grafie przepływu cyrkulatora [3]. Zarówno w jednym, jak i drugim przypadku występuje znaczna komplikacja zależności opisujących parametry cyrkulatora już dla jednostopniowego transformatora, przy czym komplikacja ta szybko się powiększa dla transformatorów wielostopniowych. Proponowana w tym opracowaniu metoda obejmuje znacznie szerszą grupę układów dopasowujących, przy czym ich liczba praktycznie nie komplikuje zależności końcowych opisujących parametry cyrkulatora. Przedstawiona metoda jest oparta na transformacji wartości własnych macierzy impedancji falowych.

EN

The method presented below has been developed for strip and microstrip circulators with multi-stage matching transformers, and the transformer may contain microwave two ports made of linear passive elements. In the circulator design methods used so far, the matching transformer was taken into account for the boundary conditions for the tangent components of the E and H fields on successive ferrite-dielectric discontinuities, dielectric-dielectric discontinuities, etc. The calculation method based on the circulator flow graph was also used. In both cases, there is a significant complication of the relationships describing the parameters of the circulator already for a single-stage transformer, and this complication increases rapidly for multi-stage transformers. The method proposed in this paper covers a much wider range of matching circuits, with the number of practically no complicated depending on the final parameters that describe the circulator. The presented method is based on the transformation of the eigenvalues of the wave impedance matrix.