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1
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Non-Wave Variations in Temperature Caused by Sound in a Chemically Reacting Gas

100%
Perelomova A., Pelc-Garska W.
Acta Physica Polonica A
|
2011
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vol. 120
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issue 3
455-461
EN
A weakly nonlinear generation of non-acoustic modes in the field of sound in a gas is considered. An exoteric chemical reaction of A → B type, which takes place in a gas, may be reversible or not. Two types of sound are considered, low-frequency and high-frequency as compared with the characteristic time of a chemical reaction. For both these cases, the governing equations of non-acoustic modes are derived and conclusions of the efficiency of their nonlinear generation by sound are made. The character of nonlinear generation of non-acoustic modes by sound depends essentially on reversibility of a chemical reaction.
2
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Total Acoustic Power of Two Concentric Clamped Circular Plates Vibrating in a Fluid

80%
Rdzanek W.
Acta Physica Polonica A
|
2015
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vol. 128
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issue 1A
A-41-A-45
EN
This study focuses on the problem of sound radiation by two concentric clamped flat plates, circular and annular, into the half-space. The system of three coupled differential equations comprising two equations of motions of plates and the wave equation, is solved exactly. Vibrations of plates are axisymmetric and time-harmonic with a single excitation frequency. The initial phase difference of excitations can be nonzero. Attenuation due to fluid loading and material damping is included. Kirchoff-Love and Kelvin-Voigt theories are applied. The effect of initial phase difference of excitations on the acoustic power radiated is examined as well as errors resulting from neglecting the fluid loading.
3
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The Low Frequency Approximation of the Sound Radiation Power of Two Vibrating Circular Pistons Embedded in Two Different Rigid Planes of a Three-wall Corner

80%
Rdzanek W., Rdzanek W., Szemela K.
|
|
vol. 125
|
issue 4A
A-135-A-143
EN
The problem of sound radiation by a system consisting of two vibrating circular pistons embedded in two of three different planes perpendicular to one another forming a three-wall corner is considered. The earlier published results dealing with the sound radiation by sources vibrating in a three-wall corner are the basis of analysis. According to the earlier studies, the exact formulae for acoustic power of radiation of two circular pistons are used. The formulae are expressed as double Fourier integrals. The active and reactive, self and mutual, components are separated from them as well as the corresponding expressions of the acoustic power of mirror images of the piston sources. The acoustic power of the two sources are expressed in the form of the Rayleigh formulae whereas, in the case of the mirror images, it is expressed in the form of the single series expansion containing spherical Bessel and Neumann functions. In the case of the mutual acoustic power of the sources, approximate formulae are presented for low frequencies. On the basis of the results obtained, the corresponding formulae valid for a two-wall corner are presented as the limiting transitions. All the results presented can be useful, e.g. in designing the room acoustics and outdoor system everywhere the free field conditions are disturbed by the acoustic waves reflected at rigid vertical walls for the wavelengths being considerably shorter than the geometric sizes of the walls.
4
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Acoustic Impedance of an Annular Piston Wobbling in a Flat Screen Around a Semi-infinite Circular Cylinder

80%
Pieczonka D., Rdzanek W., Rdzanek W.
Acta Physica Polonica A
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2013
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vol. 123
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issue 6
1078-1084
EN
A rigorous solution is presented for the problem of sound radiation by an oscillating and wobbling annular piston embedded concentrically in a perpendicular flat screen surrounding a semi-infinite circular cylindrical baffle. Two forms of the Green's function of the considered region are used. The acoustic impedance is presented in its integral form useful for numerical calculations which enable studying the effect of the acoustic waves scattering on the cylindrical baffle and the asymmetry of vibration velocity on the piston on the resultant acoustic impedance of the wobbling piston. It is shown that in the case of the vibrating piston under consideration, the reciprocity of acoustic impedance related to two modes of rigid body motion, oscillating and wobbling, does not occur.
5
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Acoustic Nearfield and Farfield for Vibrating Piston in Geometrical and Intensity Formulations

80%
Kozień M.
Acta Physica Polonica A
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2012
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vol. 121
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issue 1A
A-132-A-135
EN
In classic acoustics there are two areas identified around acoustic sources - nearfield and farfield. The nearfield is connected with the Fresnel solution and farfield - the Fraunhofer one. For each regions there are different theoretical formulae for determination of distribution of the chosen acoustic parameter. Unfortunately there is no sharply outlined border between regions. Therefore one of the important problem, is to define approximately conditions for state the border between them. The two attempts for identification are discussed, i.e. geometrical one and intensity ones. The results are shown on the vibrating circular rigid piston case.
6
Content available remote

Divergence of geometrical optics series at the boundary of its applicability: An analytical example in elementary functions (2D Gaussian beam in free space)

70%
Kravtsov Y., Buske S.
Open Physics
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2006
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vol. 4
|
issue 1
1-7
EN
An analytical example in elementary functions is presented (2D Gaussian beam diffraction in free space), which demonstrates the divergence of the geometrical optics (GO) series when the conditions for its applicability are violated. This example shows that accounting for higher terms in GO power series leads to divergence and therefore becomes completely useless beyond the boundaries of GO applicability.
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