• Journal of KSNVE
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• v.8 no.2
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• pp.274-282
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• 1998

A systematic procedure for designing a direct-radiator-type loudspeaker has been developed, based on the numerical vibro-acoustic analysis and the Taguchi method. The finite-element model of the speaker cone has been used to calculated the vibration response of the cone excited by the voice coil. The vibration displacement of the speaker cone has been converted into the vibration velocity and used as a boundary condition for the acoustic analysis. The acoustic frequency characteristics of the loudspeaker have been calculated by the boundary element method. The numerical results have been verified by the experiments carried out in an anechoic chamber. Some design parameters have been selected by using the Taguchi method, and the variations of the acoustic characteristics due to the changes of the parameter values have been examined using the numerical model.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.5
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• pp.1383-1391
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• 1996

The steady-state response for a coupled structure-acoustic-cavity systme has been investigated by numerical technique using a directly coupled finite element method(FEM) and Boundary Element Method(BEM) model. The Laplace tranformed matrix equations for the structure and the acoustic cavity are coupled directly satisfying the necessary equilibrium and compatibility conditions. The coupled FEM-BEM code is verified by comparing its prediction for an example with known analytical, numerical and experimental results. The example involves a coupled structure-acoustic-cavity system which is a box-type cavity with one end as experimentally excited pinned-pinned plate.

• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.555-561
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• 2001

A new approach to analyze the multi-domain acoustic system divided and enclosed by flexible structures is presented in this paper. The boundary element formulation of the Helmholtz integral equation is used for the internal fields and the finite element formulation for the structures surrounding the fields. We developed a numerical analysis program for the structural-acoustic coupling problems of the multi-domain system, in which boundary conditions such as the continuity of normal particle velocity and sound pressure in the structural interfaces between Field 1 and Field 2 are not needed. The validity of the numerical analysis program is verified by comparing the numerical results with the experimental ones. Example problems are included to investigate the characteristics of the coupled multi-domain system.

• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.21-30
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• 2001

The analysis system implementing a serial process from structural vibration to sound radiation has been developed using both the power flow finite element method (PFFEM) known as a new vibrational analysis technique in medium to high frequency ranges and the acoustic boundary element method (BEM) which is effective in analyzing the sound radiation problems. The vibration analysis for arbitrary shape structures composed of plates is performed, and using the vibration energy density obtained from this analysis as the velocity boundary conditions for an acoustic analysis, vibro-acoustic analysis has been processed. To verify the developed system, we select a simple structure model and compare the results of developed system with those of SYSNOISE, and also the developed system is applied for the vibro-acoustic analysis of various structures in shapes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1742-1756
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• 1997

The acoustic characteristics of a direct radiator type loudspeaker has been studied in this paper. The natural modes of the speaker cone vibration analyzed numerically by the finite element method have been verified by comparing them with experimental results. The so-ap-proved finite-element model has been used to calculate the vibration response of the cone excited by the voice coil. The vibration displacement of the speaker cone paper has been converted into the vibration velocity and used as a boundary condition for the acoustic analysis. The frequency characteristics, directivity, and sound pressure distribution of the loudspeaker have been calculated by the boundary element method. The numerical results have been verified by the experiments carried out in an anechoic chamber. The variations of the acoustic characteristics due to the changes of some design parameter values can be examined using the numerical model.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.9
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• pp.922-927
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• 2009

The transducers used in active sonar on surface ships are packed in a specific geometry in the array drum in order to meet the requirements such as the source level, directional beam pattern, etc. This paper describes the acoustic characteristics of the cylindrical array which is based on a 64 vertical staves arrangement, each stave composed 5 independent transducers. Firstly, the single transducer on the rigid baffle in the water is analyzed with the Finite Element Method. From the result of the FE analysis nodal velocities on the radiation surface is calculated and used with the boundary conditions of the transducers mounted on the array drum. Then the acoustic pressure is calculated in the field points using the Boundary Element Method and the other acoustic informations, the source level, beam pattern, near field and far-field distance, were acquired.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.938-941
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• 2004

Sound generation and radiation from the duct-rotor system are calculated numerically. The wake geometries of a two-bladed rotor are calculated by using a time-marching fiee-wake method without a non-physical model of the far wake. Acoustic free field due to a rotating rotor is obtained by Lowson's equation. Using Kirchhoff source, rotating sources are modeled as stationary ones and can be inserted in the thin body boundary element method. The Kirchhoff source is validated through calculation of acoustic pressure due to a rotating point force. The thin body boundary element method (thin body BEM) is validated through calculation of acoustic radiation of ducted dipole. Using Kirchhoff source and thin body BEM, acoustic radiation of a ducted rotating source is calculated. Acoustic shielding is observed by inserting a duct and shows different phenomena at each major frequency. Acoustic radiation of a real duct-rotor system is also calculated using this method and the ducted acoustic field is significantly different from rotor only.

• Journal of KSNVE
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• v.3 no.2
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• pp.169-178
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• 1993

Internal & External duct acoustic fields are calculated by using a finite element method. The geometry is assumed as an axisymmetric duct. External acoustic field; outside the duct, and combined internal & external acoustic fields are solved. For both cases a far field's nonreflecting boundary condition is enforced by using a wave envelope element, which is a kind of finite element. First, a pulsating sphere and an oscillating sphere problem are calculated to verify the external problems, and the results are compared with exact solutions. When the wave envelope element is applied at the far boundary, the calculated finite element solutions show good agreements with the exact solutions. Secondly, the combined internal & external duct acoustic fields are calculated and visualized when monopole sources are distributed inside the duct. It is observed that the directivity of sound intensity outside the duct is beaming toward the axis for high frequency sources.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2328-2333
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• 2010

A direct boundary element method(DBEM) is widely applied for various acoustic wave problems. But this method has numerically non-unique solutions around the eigenfrequencies of the interior Dirichlet problem for the region enveloped with the acoustic boundary. A CHIEF method had been generally adopted to resolve the non-uniqueness problem and a new technique called ICA-Ring method has been suggested recently. In this paper, the characteristics of two techniques for avoiding the non-uniqueness of DBEM are examined and numerical codes embodying both techniques are developed. Numerical calculations are also carried out for an uniformly pulsating sphere, of which the results are investigated by including the comparisons with theoretical solutions.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.489-493
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• 2007

Mmulti-domain noise analysis method using Power Flow Boundary Element Method(PFBEM) has been developed successfully. Some applications are introduced. several examples. PFBEM is a numerical analysis method formulated by applying Boundary Element Method(BEM) to Power Flow Analysis(PFA). PFBEM is very powerful in predicting noise level in medium-to-high frequency ranges. However there are restrictions in analyzing the coupled structures and multi-media. In this paper, an analysis method for multi-domain acoustic problems in the diverse acoustic fields is suggested. And the developed method is applied to the car interior and exterior multi-domain noise analysis.