• Structural Engineering and Mechanics
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• 제72권4호
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• pp.421-432
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• 2019

In high-speed railway (HSR) system, the structure-borne noise inside viaduct at low frequency has been extensively investigated for its mitigation as a research hotspot owing to its harm to the nearby residents. This study proposed a novel acoustic optimization method for declining the structure-borne noise in viaduct-like structures by separating the acoustic contribution of each structural component in the measured acoustic field. The structural vibration and related acoustic sourcing, propagation, and radiation characteristics for the viaduct box girder under passing vehicle loading are studied by incorporating Finite Element Method (FEM) with Modal Acoustic Vector (MAV) analysis. Based on the Modal Acoustic Transfer Vector (MATV), the structural vibration mode that contributes maximum to the structure-borne noise shall be hereinafter filtered for the acoustic radiation. With vibration mode shapes, the locations of maximum amplitudes for being ribbed to mitigate the structure-borne noise are then obtained, and the structure-borne noise mitigation performance shall be eventually analyzed regarding to the ribbing conduction. The results demonstrate that the structural vibration and structure-borne noise of the viaduct box girder mainly occupy both in the range within 100 Hz, and the dominant frequency bands both are [31.5, 80] Hz. The peak frequency for the structure-borne noise of the viaduct box girder is mainly caused by $16^{th}$ and $62^{th}$ vibration modes; these two mode shapes mainly reflect the local vibration of the wing plate and top plate. By introducing web plate at the maximum amplitude of main mode shapes that contribute most to the acoustic modal contribution factors, the acoustic pressure peaks at the field-testing points are hereinafter obviously declined, this implies that the structure-borne noise mitigation performance is relatively promising for the viaduct.

• 한국소음진동공학회논문집
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• 제22권7호
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• pp.676-684
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• 2012

Numerical analysis was performed to investigate the heavy-weight impact noise of apartment houses. The FEM is practical method for prediction of low-frequency indoor noise. The results of numerical analysis, the shape of the acoustic modes in room-2 are similar to that of acoustic pressure field at the fundamental frequency of acoustic modes. And the acoustic pressure was amplified at the natural frequency of the acoustic modes and structural modes. The numerical analysis result of sound pressure level at 63 Hz and 125 Hz octave-band center frequency are similar to the test results, but at 250 Hz and 500 Hz have some errors. Considering most of bang-machine force spectrum exists below 100 Hz, the noise at 250 Hz and 500 Hz are not important for heavy-weight impact noise. Thus, the FEM numerical analysis method for heavy-weight impact noise can apply to estimate heavy-weight impact noise for various building systems.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.416-421
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• 2001

This paper presents the numerical prediction of sound generated by viscous flow past a circular cylinder. The two dimensional flow field is predicted using FEM based Reynolds-averaged Navier-Stokes solver, and the calculated unsteady fluid field values are utilized by an acoustic code that implements Ffowcs Willianms-Hawkings(FW-H) equation. The integration surface used in acoustic analysis is extended from the cylinder surface to permeable surfaces. The 2D based CFD calculations overpredict the acoustic amplitude, however, if adequate correlation length is used, the predicted acoustic amplitude agrees well with experiment. The predictions using extended integral surface in FW-H equation show results that contain the characteristics of quadrupole - volume integration - noise term, and do not vary seriously with the integral surface location.

• 소음진동
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• 제3권2호
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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.

• 한국자동차공학회논문집
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• 제6권1호
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• pp.182-195
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• 1998

The relation between the vibration induced from machinery and the radiated sound is complicated. Acoustic intensity method is widely used to obtain the accuracy of noise identification. In this study, as groundwork, the complex acoustic intensity method is performed to identify noise source and transmission path on different free space point source fields. From the numerical analysis for these simple fields, it is possible to predict the sound field characteristics which noise sources are related with each other, and certificate the validity of complex acoustic intensity. As an industrial application, the complex acoustic intensity method is applied a diesel engine to identify sound radiation characteristics in the near field.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.763-766
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• 2002

A BEM is highly efficient method in the sense of economic computation. However, boundary integration is not easy for the complex and moving surface e.g. in a rotating blade. Thus, Kirchhoff surface is designed in an effort to overcome the difficulty resulting from complex boundary conditions. A Kirchhoff surface is a fictitious surface which envelopes acoustic sources of main concern. Acoustic sources may be distributed on each Kirchhoff surface element depending on its acoustic characteristics. In this study, an axial fan is assumed to have loading noise as a dominant source. Dipole sources can be computed based on the FW-H equation. Acoustic field is then computed by changing Kirchhoff surface on which near-field is implemented, to analyze the effect of Kirchhoff surface on it.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.772-777
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• 2002

A BEM is highly efficient method in the sense of economic computation. However, boundary integration is not easy for the complex and moving surface e.g. in a rotating blade. Thus, Kirchhoff surface is designed in an effort to overcome the difficulty resulting from complex boundary conditions. A Kirchhoff surface is a fictitious surface which envelopes acoustic sources of main concern. Acoustic sources may be distributed on each Kirchhoff surface element depending on its acoustic characteristics. In this study, an axial fan is assumed to have loading noise as a dominant source. Dipole sources can be computed based on the FW-H equation. Acoustic field is then computed by changing Kirchhoff surfaces on which near-field is implemented, to analyze the effect of Kirchhoff surface on it.

• 대한기계학회논문집
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• 제10권5호
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• pp.601-610
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• 1986

본 연구에서는 음향학적 고찰로써 최근 디지를 처리기술의 발달에 따른 근접 한 2점의 음압으로 부터 테니스 라켓의 공기입자속도를 근사적으로 구하기 위하여 두 개의 마이크로폰을 이용하여 계산된 음향인텐시티는 구물의 오무드 해석법에 의해 구 해진 테니스 라켓의 동적 특성과 비교 검토함으로써 진동과 음의 발생기구를 구명하고 측정계의 비접촉에 의한 테니스 라켓의 동적 거동을 규명하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 추계학술대회 논문집
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• pp.569-569
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• 2014

The interior vehicle noise due to the exterior aerodynamic field is an important topic in the acoustic design of a car. The air flow detached from the A-pillar and impacting the side windows are of particular interest as they are located close to the driver / passenger and provides a lower insulation index than the trimmed car body parts. This paper presents a numerical analysis method for a simplified vehicle model. The internal air cavity including trim component are included in the simulation. The car body includes the windshield and two side windows. The body is made of aluminum and trimmed with porous layers. The methodology proposed in this paper relies on two steps: the first step involves the computation of the exterior flow and turbulence induced non-linear acoustic field using CFD Code. The second step consists in the computation of the vibro-acoustic transmission through the window using the finite element vibro-acoustic solver Actran.

• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.145-152
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• 2004

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-frequency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.