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1
Content available The Radiation Efficiency Measurements of Real System of a Thin Circular Plate Embedded Into a Thick Square Baffle
Szemela K., Rdzanek W. P., Żyłka W.
Archives of Acoustics
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2018
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Vol. 43, No. 3
413--423
EN
Most of sound sources are complex vibroacoustic objects consist of numerous elements. Some coupled vibrating plates of different shapes and sizes can be easily found in urban environments. The main aim of this study is to determine the sound radiation of coupled plates system of practical importance. The investigated vibroacoustic system consist of a thin circular plate coupled with a thick flat baffle with a circular hole. The circular plate has been mounted to the baffle’s hole using screws and two steel rings. The measurement setup was located inside a semi-anechoic chamber to assure the free field conditions. It was necessary to take into account the whole system surface to obtain the radiation efficiency based on the Hashimoto’s method. Such an approach can be troublesome and time-consuming. Therefore, the criterion has been proposed which allows the vibration velocity measurements and calculations to be performer only for the thin plate’s area. An alternative approach has been proposed based on the classical Rayleigh integral formula. Its advantage is a simpler implementation in a computer code. The obtained results have been compared with the theoretical results obtained for the elastically supported circular plate. A good agreement has been obtained at low frequencies.
2
Content available Sound Radiation by a Cylindrical Open Cavity with a Surface Source at the Bottom
Szemela K.
Archives of Acoustics
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2018
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Vol. 43, No. 1
49--60
EN
The rigorous solution describing the sound radiation by an arbitrary surface source located at the bottom of a cylindrical open cavity embedded in a flat baffle has been obtained. The open cavities of different shapes can be found in some architectural structures as well as are components of sensors, musical instruments and vehicles. The presented formulas have been expressed in the form of Infinite sums. To use them, the infinite sums have to be truncated to the finite number of terms. Therefore, in practice, the results obtain based on the proposed solution are not exact and their accuracy is determined by the truncation error. The use of presented formulas is an alternative method for the finite element method (FEM). However, taking into account that the calculation efficiency of FEM rapidly decrease when a volume of considered region increases, the obtained in this study solution can be more useful in some practical cases. The approximated formula of a high computational efficiency has been presented for the sound pressure in the far field. The sound radiation has been analyzed for a rectangular piston as a sound source. The influence of cavity depth ratio on the radiation efficiency has been investigated. The cases for which the cavity radiation efficiency can be approximately calculated from the formula valid for a baffled sound source have been determined.
3
Content available Sound Radiation from a Surface Source Located at the Bottom of the Wedge Region
Szemela K.
Archives of Acoustics
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2015
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Vol. 40, No. 2
223--234
EN
Applying rigorous analytical methods, formulas describing the sound radiation have been obtained for the wedge region bounded by two transverse baffles with a common edge and bottom. It has been assumed that the surface sound source is located at the bottom. The presented formulas can be used to calculate the sound pressure and power inside the wedge region. They are valid for any value of the wedge angle and represent a generalization of the formulas describing the sound radiation inside the two and three-wall corner region. Moreover, the presented formulas can be easily adapted for any case when more than one sound source is located at the bottom. To demonstrate their practical application, the distribution of the sound pressure modulus and the sound power have been analyzed in the case of a rectangular piston located at the wedge’s bottom. The influence of the transverse baffle on the sound power has been investigated. Based on the obtained formulas, the behaviour of acoustic fields inside a wedge can be predicted.
4
Content available Acoustic Power Radiated by a System of Two Vibrating Circular Membranes Located at the Boundary of Three-Wall Corner Spatial Region
Szemela K., Rdzanek W. P., Rdzanek W. J.
Archives of Acoustics
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2012
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Vol. 37, No. 4
463-473
EN
Two vibrating circular membranes radiate acoustic waves into the region bounded by three infinite baffles arranged perpendicularly to one another. The Neumann boundary value problem has been inves- tigated in the case when both sources are embedded in the same baffle. The analyzed processes are time harmonic. The membranes vibrate asymmetrically. External excitations of different surface distributions and different phases have been applied to the sound sources’ surfaces. The influence of the radiated acoustic waves on the membranes’ vibrations has been included. The acoustic power of the sound sources system has been calculated by using a complete eigenfunctions system.
5
Content available Acoustic Pressure Radiated by a Circular Membrane Into the Quarter-Space
Rdzanek W. P., Szemela K., Pieczonka D.
Archives of Acoustics
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2011
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Vol. 36, No. 1
121-139
EN
The Neumann boundary value problem for the Helmholtz equation within the quarter-space has been considered in this paper. The Green function has been used to find the acoustic pressure amplitude as the approximation valid within the Fraunhoffer’s zone for some time-harmonic steady state processes. The low fluid loading has been assumed and the acoustic attenuation has been neglected. It has also been assumed that the vibration velocity of the acoustic particles is small as compared with the sound velocity in the gaseous medium.
6
Content available remote Acoustic power radiated into the quarter-space by a circular membrane with an asymmetric excitation
Rdzanek W. P., Rdzanek W. J., Szemela K.
Archives of Acoustics
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2009
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Vol. 34, No. 1
75-94
EN
A circular membrane excited asymmetricaly is vibrating and radiating acoustic waves into the quarter-space limited by two rigid baffles arranged perpendicularly to one another. These processes are time harmonic. The classical Neumann boundary value problem has been solved using the complete eigenfunctions system together with the corresponding coupling matrix and including the acoustic attenuation effect.
7
Content available The acoustic radiation impedance of a circular membrane vibrating near the three-wall corner
Rdzanek W. P., Rdzanek W. J., Szemela K.
Hydroacoustics
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2008
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Vol. 11
339-352
EN
A flat circular membrane is located near the three- wall corner, limited by the three rigid baffles arranged perpendicularly to each other. The problem of sound radiation has been solved using the spectral form of the Green function for this Neumann boundary value problem together with the complete eigenfunction system of the axisymmetric and asymmetric modes of the membrane is excited by a surface vibrating harmonically with respect to time within the vacuum. The membrane is excited by a surface force. The acoustic attenuation 3399effect has been taken into account as well as the influence of the corner baffles. The resultant sound pressure and the resultant acoustic impedance have been presented as their eigenfunction series. The modal, self and mutual, radiation resistance has been presented in the form of the approximation valid within the low frequency vibration range. The low frequency approximation for the modal radiation reactance has been obtained on the basis of the radiation resistance using the Hilbert transform.
8
Content available The Modal Low Frequency Noise of an Elastically Supported Circular Plate
Rdzanek W. P., Rdzanek W. J., Engel Z., Szemela K.
International Journal of Occupational Safety and Ergonomics
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2007
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Vol. 13, No. 2
147--157
EN
The modal low frequency noise generated by a vibrating elastically supported circular plate embedded into a flat infinite baffle has been examined. The main aim of this study is the analysis of the radiation efficiency. Low frequency approximated formulas have been presented. They are valid for all the limiting boundary conditions of the plate with its edge clamped, guided, simply supported or free as well as for all the intermediate axisymmetric boundary configurations. The formulas are expressed in the elementary form, useful for numerical computations. They are a generalization of some earlier published results. First, they are valid for axisymmetric and asymmetric modes since both kinds of modes play an important role in the low frequency range. Second, a single formula for the radiation efficiency, valid for all the axisymmetric boundary configurations, has been proposed. A numerical example for the sound power radiation has been given for some hatchway covers mounted on a ship deck.
9
Content available remote Sound pressure radiation of a circular piston located at a two- and three-wall corners
Rdzanek W. P., Szemela K., Pieczonka D.
Archives of Acoustics
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2007
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Vol. 32, No. 4
883--893
EN
This paper focuses on the far eld approximation of the steady state sound pressure radiated by a at circular piston into the region bounded by some at rigid bafes. The two Neumann boundary value problems have been considered for the regions of two- and three-wall corners, separately. The Green function in its Fourier representation has been used together with the Sommerfeld radiation condition which has given the sound pressure approximation in the form of some useful elementary formulations. The boundary value problems often appear in the situation when the sound source is located in the vicinity of the Earth and some vertical walls, e.g. the sound barriers, the building walls, etc.
10
Content available remote The acoustic power radiated by a circular membrane excited for vibration both by means of the edge and by external surface load
Szemela K., Rdzanek W. P., Rdzanek W.
Archives of Acoustics
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2005
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Vol. 30, No. 1
109-119
EN
In this paper the acoustic power of the circular membrane, excited both by the edge and external exciting forces uniformly distributed over the whole surface, is examined. Some different amplitudes of exciting factors and some differences between the phases of excitations were considered. It has been assumed that the source of a sound is located in a flat, rigid and infinite baffle and is sourrounded by a lossless and homogeneous fluid medium. The vibrations are axisymmetric and time-harmonic. Employing the Cauchy's theorem of residues and asymptotic formulae for the Bessel functions, the asymptotes for active and reactive power consisting of elementary functions are obtained. The acoustic power radiated by the membrane was shown graphically in terms of the parameters describing both kinds of excitations.
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