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1

Modelling of the acoustic wave scattering on the aircraft surface using the boundary element method

Nowicki Dawid, Suder-Dębska Katarzyna, Czajka Ireneusz

Vibrations in Physical Systems

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2023

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Vol. 34, nr 1

art. no. 2023107

EN

Sound localization tools are important in the environmental protection and the human searches. The article is one of the stages of the implementation of the concept of using aircraft to localize sound sources. The use of a fixed-wing aircraft instead of a multirotor would increase the total flight time, and expand the surveyed area. It is important to determine the most favourable positions of the receivers on the surface of the aircraft. The scattering effects of the sound waves coming from the ground source and aircraft engine on the acoustic field on the aircraft surface are not homogeneous. In the article the authors present the modelling of the scattering of the sound waves over the airplane surface with the usage of boundary element methods. After determining the effects from the sound source on earth and from the aircraft engine the conclusion was made, that the influence from the engine noise is greater than that from the ground source, and in order to localize the low amplitude signals, the aircraft need to glide. Considering only the effects of the ground source, the optimal areas for the microphones placement were determined.

2

Sound Scattering by an Elastic Spherical Shell and its Cancellation using a Multi-pole Approach

Avital E. J., Bholah N. D., Giovanelli G. C., Miloh T.

Archives of Acoustics

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2017

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Vol. 42, No. 4

697--705

EN

The scattering and transmission of sound by an elastic spherical shell is considered when it is subject to an incoming monochromatic planar wave. It is aimed to cancel the sound scattering using combinations of multi-pole sources located at the centre of a shell filled with compressible fluid. Assuming linear acoustics and structural dynamics, exact solutions are derived for total elimination of the sound scattering for three cases: a free-space, near a hard ground or near a free-surface, where in the last two cases it is assumed that the incoming wave propagates normal to the interface to maximize sound reflection back unto the source of the incoming wave. An elastic spherical shell of 1 m radius embedded in water and filled with air or oil is analysed to show the dominance of low-mode numbers for frequencies of less than 10 kHz and thus demonstrate the ability of this approach to damp acoustic scattering by means of low-order multi-poles inside the shell. Contour and mode distribution plots are also given and analysed.

3

The Characteristic of Sound Reflections from Curved Reflective Panels

Szeląg A., Kamisiński T., Lewińska M., Rubacha J., Pilch A.

Archives of Acoustics

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2014

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Vol. 39, No. 4

549--558

EN

The paper presents the verification of a solution to the narrow sound frequency range problem of flat reflective panels. The analytical, numerical and experimental studies concerned flat panels, panels with curved edges and also semicircular elements. There were compared the characteristics of sound reflected from the studied elements in order to verify which panel will provide effective sound reflection and also scattering in the required band of higher frequencies, i.e. above the upper limit frequency. Based on the conducted analyzes, it was found that among some presented solutions to narrow sound frequency range problem, the array composed of panels with curved edges is the most preferred one. Nevertheless, its reflection characteristic does not meet all of the requirements, therefore, it is necessary to search for another solution of canopy which is effective over a wide frequency range.

4

Analysis of Spectral Characteristics of Sound Waves Scattered from a Cracked Cylindrical Elastic Shell Filled with a Viscous Fluid

Piddubniak O., Piddubniak N.

Archives of Acoustics

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2013

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Vol. 38, No. 3

335--350

EN

The scattering of plane steady-state sound waves from a viscous fluid-filled thin cylindrical shell weak- ened by a long linear slit and submerged in an ideal fluid is studied. For the description of vibrations of elastic objects the Kirchhoff-Love shell-theory approximation is used. An exact solution of this problem is obtained in the form of series with cylindrical harmonics. The numerical analysis is carried out for a steel shell filled with oil and immersed in seawater. The modules and phases of the scattering amplitudes versus the dimensionless wavenumber of the incident sound wave as well as directivity patterns of the scattered field are investigated taking into consideration the orientation of the slit on the elastic shell surface. The plots obtained show a considerable influence of the slit and viscous fluid filler on the diffraction process.

5

How does the size distribution of living material influence sound scattering in the sea?

Szczucka J.

Hydroacoustics

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2003

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Vol. 6

41--48

EN

Evaluation of the relative contribution of the living objects with different sizes to sound scattering at sea is presented. The relative contribution to the total scattering depends on two factors: size spectrum of oceanic biomass and individual scattering properties of organisms. Various coefficients in the power function describing dependence of biomass concentration on individual size are tested and compared. Simple high-pass model of scattering is used. Flesh and swimbladder contributions are considered separately.