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

2017 ◽  
Vol 42 (4) ◽  
pp. 697-705
Author(s):  
Eldad Jitzchak Avital ◽  
Neeshtha Devi Bholah ◽  
Giuseppe Cortez Giovanelli ◽  
Touvia Miloh
Keyword(s):  
Free Surface ◽  
Spherical Shell ◽  
Structural Dynamics ◽  
Acoustic Scattering ◽  
Sound Scattering ◽  
Incoming Wave ◽  
Elastic Spherical Shell ◽  
Sound Reflection ◽  
Planar Wave ◽  
Total Elimination

Abstract 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.

scholarly journals Sound Scattering and Its Reduction by a Janus Sphere Type

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
Deliya Kim ◽  
Eldad Jitzhak Avital ◽  
Touvia Miloh
Keyword(s):  
Free Surface ◽  
Acoustic Impedance ◽  
Sound Field ◽  
Acoustic Power ◽  
Sound Scattering ◽  
Incoming Wave ◽  
Soft Zone ◽  
Pressure Line ◽  
Soft Surface ◽  
Boundary Location

Sound scattering by a Janus sphere type is considered. The sphere has two surface zones: a soft surface of zero acoustic impedance and a hard surface of infinite acoustic impedance. The zones are arranged such that axisymmetry of the sound field is preserved. The equivalent source method is used to compute the sound field. It is shown that, by varying the sizes of the soft and hard zones on the sphere, a significant reduction can be achieved in the scattered acoustic power and upstream directivity when the sphere is near a free surface and its soft zone faces the incoming wave and vice versa for a hard ground. In both cases the size of the sphere’s hard zone is much larger than that of its soft zone. The boundary location between the two zones coincides with the location of a zero pressure line of the incoming standing sound wave, thus masking the sphere within the sound field reflected by the free surface or the hard ground. The reduction in the scattered acoustic power diminishes when the sphere is placed in free space. Variations of the scattered acoustic power and directivity with the sound frequency are also given and discussed.

Calculation on Acoustic Scattering of Viscoelastic Layer Coupling with Elastic Shell

2012 ◽  
Vol 248 ◽  
pp. 107-113
Author(s):  
Zhong Kun Jin ◽  
Tong Qing Wang
Keyword(s):  
Boundary Condition ◽  
Spherical Shell ◽  
Elastic Shell ◽  
Acoustic Scattering ◽  
Impedance Boundary Condition ◽  
Target Strength ◽  
Viscoelastic Layer ◽  
Impedance Boundary ◽  
Elastic Spherical Shell ◽  
Element Method

This paper is devoted to numerical research on coupling between elastic spherical shell and the coated viscoelastic layer as well as the scattering of incident plane wave by the double-layer spherical shell. The scattering sound field is solved based on impedance boundary condition by boundary element method (BEM). Dynamic finite element method (FEM) is used to numerically simulate the acoustic impedance boundary condition which involved in the coupled spherical shell. Impedance distribution for elastic spherical shell and elastic spherical shell coated viscoelastic layer is calculated and its effect on the target strength (TS) is discussed finally.

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