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1
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Acousto-Electromagnetic Analogies in Diffraction Phenomena Occurring in the Semi-Infinite Cylindrical Waveguide

100%
Snakowska A.
Acta Physica Polonica A
|
2009
|
vol. 116
|
issue 3
410-413
EN
The paper presents analogies between acoustic and electromagnetic wave field occurring in limited areas, such as waveguides, when electromagnetic waves are not purely transversal. The acousto-electromagnetic analogies exist in structures such as plane, rectangular or cylindrical infinite waveguides, if the fields are analysed by means of potentials - the velocity potential for sound waves and the Hertz potentials for electromagnetic waves. It has been demonstrated why these analogies between the potentials representing solutions of the wave equation with adequate boundary conditions and expressed as sums of admissible duct modes do fail, in general, for the semi-infinite cylindrical duct, and why they remain valid when the propagating electromagnetic mode is axisymmetric.
2
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Modification of the Measurement Setup for Examination of Acoustic Field Distribution Inside Cylindrical Ducts for Axisymmetric Excitation

51%
Gorazd Ł., Jurkiewicz J., Raab S., Snakowska A.
Acta Physica Polonica A
|
2013
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vol. 123
|
issue 6
1085-1089
EN
The aim of the paper is to present results of examination of the acoustic pressure field inside a model of a cylindrical duct. Measurements of the root mean square acoustic pressure were carried out using a new measurement setup, first in conditions allowing for propagation of the plane wave only, and next - by increasing the excitation frequency - with successive higher modes also taken in account. Two types of hard-walled cylindrical ducts were examined corresponding to mathematical models known as the infinite duct and the semi-infinite duct. A dedicated measurement setup is presented as well as the successive stages of its modification. In order to verify the modified measuring system, the first stage of the research work consisted in excitation of the axisymmetric modes only and assessing the degree of symmetry represented by the measurement data Significant improvement of the compatibility of the obtained measurement results with theoretical predictions was observed in the explored frequency band 800-5500 Hz that for the duct inside radius of a=0.077 m corresponded to the reduced frequency range 1.13
3
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The Application of Double-layer Curtains for Shaping Acoustics of Concert Halls

51%
Pilch A., Karlińska A., Snakowska A., Kamisiński T.
Acta Physica Polonica A
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2014
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vol. 125
|
issue 4A
A-113-A-116
EN
Requirements concerning adjustment of acoustical parameters are nowadays more and more frequently numbered among design assumptions adopted for newly constructed concert halls and other auditoriums planned to play different functions. Investors usually require that the newly designed interiors can be used for such different purposes as playing orchestral music, performing theatre spectacles, screening movies, or holding lectures. This means the necessity to undertake studies on new technologies allowing to excert effective control over acoustics of multipurpose auditoriums. This paper proposes to use acoustic curtains as an effective means of modification of acoustic absorptivity of rooms. A design solutions for such curtains is described together with basics of the theory allowing to predict their acoustic properties. Results of sound absorption coefficient calculations performed for selected systems on the grounds of airflow resistivity values assumed for the used fabrics are verified by means of results of measurements performed in the impedance tube. It is proven that double-layer curtains show more balanced sound absorption characteristics compared to single-layer curtains and therefore represent a more convenient option when used for acoustical adaptation of rooms. Based on model studies, design solutions with double-layer curtains is developed for two concert halls that allow to adjust acoustic properties of the interiors to the required functions.
4
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Acoustic Impedance of Outlet of a Hard-Walled Unbaffled Cylindrical Duct for Multimode Incident Wave

51%
Jurkiewicz J., Snakowska A., Smolik D.
Acta Physica Polonica A
|
2011
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vol. 119
|
issue 6A
1061-1067
EN
In the paper, the specific acoustic impedance of outlet of an unbaffled duct for incident wave composed of one or many circumferential cut-on duct modes has been derived and presented on graphs. When considering the multimode excitation the equal energy per mode principle and random phases have been assumed. Experimentally verified assumption on equal energy per mode allows for quantitative analysis of the sound field and thus provides more physical insight into the in-duct and out-duct phenomena. The assumption of random phase was implemented by means of the Monte Carlo method and so the expected value, the standard deviation and the percentile curves of the impedance were presented. Numerical data obtained according to the derived theoretical formulae for single and multimode incident wave manifest strong modal character and dependence on the modes phases. The assumption of multimode incident wave has brought the theoretical model closer to what is being observed in practice, especially when ducts of large radius, such as heating and air conditioning systems or turbojet engines, are considered.
5
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Open End Correction for Arbitrary Mode Propagating in a Cylindrical Acoustic Waveguide

51%
Snakowska A., Jurkiewicz J., Smolik D.
Acta Physica Polonica A
|
2011
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vol. 120
|
issue 4
736-739
EN
The paper presents a method of theoretical derivation and numerical calculation of the open-end correction coefficient for an arbitrary cut-on mode propagating in acoustic waveguide. Actually, the so-called open-end correction coefficient of acoustic tube, frequently discussed in literature, refers to specific conditions, when the wave heading the outlet is the plane wave. It follows from the fact that the plane wave is a commonly applied approximation when considering phenomena in duct-like devices or systems (tubes, musical instruments, heating or ventilation systems). The aim of the paper is to extend the concept of the open-end correction on the so-called higher Bessel modes, that under some conditions can also propagate in a duct. Theoretical results, forming the basis for numerical calculations, were obtained by considering diffraction at the duct end and applying the Wiener-Hopf factorization method. As a result, the formula for the acoustic field inside the duct was derived. For each Bessel mode present in the incident wave the reflected wave is composed of all cut-on modes of the same circumferential order. Each mode present in the reflected wave is characterized by the complex reflection/coupling coefficient, argument of which describes phase change at the duct end and therefore the open-end correction coefficient can be attributed to each coupled pair of modes.
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