• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.6
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• pp.8-14
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• 1998

The derivation of the dual integral equation in the spectral domain, which has total fields of the interfaces as unknowns, is investigated. It is analytically shown that the derivation of the dual integral equation is equivalent to deriving the Helmholtz-Kirchhoff integral equation from the Wiener-Hopf integral equation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.915-918
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• 2005

Acoustic holography uses Kirchhoff·Helmholtz integral equation and Green's function which satisfies Dirichlet boundary condition Applications of acoustic holography have been taken to the sound field neglecting the effect of flow. The uniform flow, however, changes sound field and the governing equation, Green's function and so on. Thus the conventional method of acoustic holography should be changed. In this research, one possibility to apply acoustic holography to the sound field with uniform flow is introduced through checking for the plane wave in a duct. Change of Green's function due to uniform flow and one method to derive modified form of Kirchhoff·Heimholtz integral is suggested for 1-dimensional sound field. Derivation results show that using Green's function satisfying Dirichlet boundary condition, we can predict sound pressure in a duct using boundary value.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.916-919
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• 2008

This paper deals with a means to reproduce sound field by using Kirchhoff-Helmholtz integral equation. We control boundary value or generate sound sources on the boundary in order to control the sound field as we want. The method assumes that there is a unique relation between sound field and its boundary should. Otherwise the reproduced sound field is different from what we want generate; the original sound field. Half-infinite sound field and finite sound field are considered and whether the uniqueness is hold or not and how the reproduced field is generated are discussed in each case.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1702-1707
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• 2003

Absorptive material arrangement method for effective interior noise control is proposed. Sound field with arbitrary boundary condition is formulated by Kirchhoff-Helmholtz integral equation. A simple example such as a rectangular cavity will present physical meaning between changing boundary condition and control of sound field. The effect of changing boundary condition is expressed in modal admittance. From this formulation, an admittance map is presented. The admittance map is the figure to represent position where absorptive material is attached. The admittance map can be assigned to each resonant frequency. There, however, may be common area of those maps. Then, frequency robust arrangement of absorptive material in noise control will be presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1317-1322
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• 2001

What changes in the eigen values and eigen functions are produced if the boundary surface S is no longer rigid but has a specific acoustic admittance which may vary from point to point on S. In this paper, changes in eigen values and eigen functions are derived by using Kirchhoff-Helmholtz integral equation. And acoustic potential energy, which is representative measure describing the physical quantity in cavity, is defined. Acoustic potential energy can be divided into primary one and secondary one. Primary one is the acoustic potential energy through unchanged eigen functions, and secondary one is through changed eigen functions. Using these two term, we can find the eigenvalue problem, which gives the control performance when the boundary condition is changed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1062-1073
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• 2007

Acoustic Target Strength (TS) is a major parameter of the active sonar equation, which indicates the ratio of the radiated intensity from the source to the re-radiated intensity by a target. In developing a TS equation, it is assumed that the radiated pressure is known and the re-radiated intensity is unknown. This research provides a TS equation for polygonal plates, which is applicable to near field acoustics. In this research, Helmholtz-Kirchhoff formula is used as the primary equation for solving the re-radiated pressure field; the primary equation contains a surface (double) integral representation. The double integral representation can be reduced to a closed form, which involves only a line (single) integral representation of the boundary of the surface area by applying Stoke's theorem. Use of such line integral representations can reduce the cost of numerical calculation. Also Kirchhoff approximation is used to solve the surface values such as pressure and particle velocity. Finally, a generalized definition of Sonar Cross Section (SCS) that is applicable to near field is suggested. The TS equation for polygonal plates in near field is developed using the three prescribed statements; the redection to line integral representation, Kirchhoff approximation and a generalized definition of SCS. The equation developed in this research is applicable to near field, and therefore, no approximations are allowed except the Kirchhoff approximation. However, examinations with various types of models for reliability show that the equation has good performance in its applications. To analyze a general shape of model, a submarine type model was selected and successfully analyzed.

• The Journal of the Acoustical Society of Korea
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• v.31 no.4
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• pp.214-224
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• 2012

The objective of this paper is to design multichannel spherical loudspeaker array by considering various positioning methods such as Gaussian grid, Lebedev grid and packing method. For the spatial sound manipulation, which is to make desired sound field by controling multiple sound sources, the Kirchhoff- Helmholtz integral states that sound fields can be reproduced in terms of infinite control sources on the integral surface. But since we cannot control infinite number of sources for the implementation, we have to allocate finite number of sound sources which can approximately act as infinite number of sources. To manipulate sound field inside of a sphere (which is typical example of three dimensional array) by controlling sound sources on the surface, three methods of allocating sound sources, which are Gaussian grid, Lebedev grid and packing method, are reviewed. For each geometry, the performances of manipulation rendered by time-reversal operator and higher-order ambisonics are compared.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.309.1-312
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• 1998

일반적으로 음향 문제에 상용되는 경계요소법은 Kirchhoff-Helmholtz 적분 방정식에 약특이성과 강특이성의 커널을 갖고 있어, 경계면에 매우 근접한 음장을 해석할 때 수치 적분 과정에서 큰 오차를 유발한다. 본 연구에서는 평면파 성분을 이용하여 약특이성 방정식 및 특이성이 제거된 음장 음압의 과도한 오차는 약특이성 경계 적분 방정식의 적용으로 제거될 수 있었다. 부드러운 경계면을 가진 경우는 모든 특이성의 제거가 가능하여 특이성 처리를 위한 특별한 처리가 불필요하게 되었다. 제안된 방법을 검증하기 위하여 몇 가지 단순한 모델에 대하여 경계 요소 계산을 수행하였고, 경계면 부근의 근접 음장에서 음압 예측의 정확도가 향상되는 결과를 얻었다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.791-796
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• 2003

Some basic guidelines for changing non-uniform boundary condition in an acoustically small cavity are presented. In this paper, modal summation technique is used to represent inside sound field. From this formulation, corner effect is defined and proposed. The corner in a cavity is good position for changing boundary condition effectively. Impedance circle with same absorption coefficient is defined to find appropriate impedance of absorptive material for better noise control performance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.9
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• pp.930-936
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• 2008

Fluid loading of a vibrating cylindrical shell has influence on natural frequencies and vibration magnitudes of the shell and the acoustic pressure of fluid. The vibroacoustics of fluid-filled cylindrical shells need the coupled solution of Helmholtz equation and governing equation of a cylindrical shell with boundary conditions. This paper proposed the wall impedance of fluid-filled axisymmetric cylindrical shells, focusing on the inner fluid/shell interaction. To propose the impedance, shell displacements used the linear combination of in vacuo shell modes. Acoustic pressure prediction of fluid used Kirchhoff-Helmholtz integral equation with Green's function of the plane mode. For the demonstration of the proposed results, numerical applications on mufflers were conducted.