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The Radiation Efficiency Measurements of Real System of a Thin Circular Plate Embedded Into a Thick Square Baffle

Wojciech P. Rdzanek Krzysztof Szmela Wojciech Żyłka
Archives of Acoustics | 2018 | vol. 43 | No 3 | 413-423 | DOI: 10.24425/123913
Keywords radiation efficiency measurements Hashimoto’s method coupled plates
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Abstract

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 performed 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.

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Authors and Affiliations

Wojciech P. Rdzanek
Krzysztof Szmela
Wojciech Żyłka

The Effect of Plate Discretization on Accuracy of the Sound Radiation Efficiency Measurements

Karolina Kolber Anna Snakowska Michał Kozupa
Archives of Acoustics | 2014 | vol. 39 | No 4 | 511-518 | DOI: 10.2478/aoa-2014-0055
Keywords sound radiation efficiency sound radiation from plates Discrete Calculation Method
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Abstract

This paper deals with the problem of the effect of discretization level and certain other parameters characterizing the measurement setup on accuracy of the process of determination of the sound radiation efficiency by means of the Discrete Calculation Method (DCM) described by Hashimoto (2001). The idea behind DCM consists in virtual division of an examined sound radiating structure into rectangular elements each of which is further assumed to contribute to the total radiation effect in the same way as a rigid circular piston having the surface area equal to this of the corresponding virtual element and vibrating in an infinite rigid baffle. The advantage of the method over conventional sound radiation efficiency measurement techniques consists in the fact that instead of acoustic pressure values, source (plate) vibration velocity amplitude values are measured in a selected number of regularly distributed points. In many cases, this allows to determine the sound radiation efficiency with sufficient accuracy, especially for the low frequency regime. The key part of the paper is an analysis of the effect of discretization level (i.e. the choice of the number of points at which vibration amplitude measurements are to be taken with the use of accelerometers) on results obtained with the use of the method and their accuracy. The problem of determining an optimum level of discretization for given excitation frequency range is a very important issue as the labor intensity (time-consuming aspect) of the method is one of its main flaws. As far as the technical aspect of the method is concerned, two different geometrical configurations of the measurement setup were tested.
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Authors and Affiliations

Karolina Kolber
Anna Snakowska
Michał Kozupa

Sound Radiation Characteristics of Acoustically Thick Composite Cylinders and Their Experimental Verification

S. Josephine Kelvina Florence K. Renji
Archives of Acoustics | 2021 | vol. 46 | No 3 | 519-530 | DOI: 10.24425/aoa.2021.138144
Keywords radiation resistance radiation efficiency cylindrical shells composites ring frequency critical frequency SEA
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Abstract

Cylindrical shells made of composite material form one of the major structural parts in aerospace structures. Many of them are acoustically thick, in which the ring frequencies are much higher than their critical frequencies. In this work, sound radiation behaviour of acoustically thick composite cylinders is presented. Based on the structural and acoustic wave number diagrams, the modal average radiation resistances in the frequency band of interest are theoretically determined. The structural wavenumbers are determined considering transverse shear deformation. The results show lesser sound radiation between the critical and ring frequencies, and significant sound radiation near the ring frequency and beyond. In the absence of the present results the radiation efficiency is considered to be unity at all frequencies beyond the critical frequency, including near the ring frequency. The radiation resistances of the same cylinder are determined experimentally and they are in very good agreement with the theoretical estimates. As part of this investigation, an expression for determining the ring frequency of composite cylinder is also presented.
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Authors and Affiliations

S. Josephine Kelvina Florence
1
K. Renji
2
  1. Structures Group, U. R. Rao Satellite Centre, Bangalore, India-560017
  2. Advanced Technology Development Group, U. R. Rao Satellite Centre Bangalore, India-560017

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