• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.450-451
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• 2013

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.482-484
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• 2014

국내의 슬라브도상, 자갈도상의 소음현안에 부합하여 소음저감설계 및 저감장치와 저감구조를 개바할 수 있는 합리적인 소음계산 및 영향인자 규명 모델을 현 모델과 더불어 발전시키고자 하며, 그의 한 예로 고속철도의 통과소음 측정 및 분석결과와 소음원 기여도 기술을 이용한 분석결과를 통하여 레일소음의 특성을 고찰하였다.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.250-261
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• 2023

In this study, the noise contributions by the duct, stator and rotor, which are the propulsor components, are evaluated to identify the flow noise source in cavitation and non-cavitation conditions on pumpjet propulsion and the noise levels in both conditions are compared. The unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equation based on the homogeneous mixture assumption is applied on the suboff submarine hull and pumpjet propeller in the cavitation tunnel, and the Volume of Fluid (VOF) method and Schnerr-Sauer cavitation model are used to describe the two-phase flow. Based on the flow simulation results, the acoustic analogy formulated by Ffowcs Williams and Hawkings (FW-H) equation is applied to predict the underwater radiated noise. The noise contributions are evaluated by using the three types of impermeable integral surface on the duct, stator and rotor, and the two types of permeable integral surface surrounding the propulsor. As a result of noise prediction, the contribution by the stator is insignificant, but it affects the generation of flow noise source due to flow separation in the duct and rotor, and the noise is predominantly radiated into the upward and right where the flow separations are. Also, the noise is radiated into the thrust direction due to pressure fluctuation between suction and pressure sides on the rotor blades, and the it can be seen that the cavitation effect into the noise can be considered through the permeable integral surface.

• The Journal of the Acoustical Society of Korea
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• v.38 no.1
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• pp.73-81
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• 2019

This paper proposes an acoustical inversion method using cepstrum analysis of underwater ship noise. Through the cepstrum analysis, multipath structure can be extracted from the recorded ship noise. The multipath structure comes from interferences between a direct arrival and multiple reflections from the sea surface and the bottom. The acoustic inversion is the optimization process to find the best parameters which show good correlation between cepstrums of the measured signal and the replica. The inversion method was applied to the underwater ship radiated noise data measured at Straits of Korea in order to estimate the acoustic center of the ship and the hydrophone position. The inversion results showed good agreement with the measured information.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.4
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• pp.307-314
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• 2008

Loading noise generated by steady aerodynamic force exerted on the rotating body surface is theoretically analyzed and its radiation characteristics is examined as a fundamental research of helicopter rotor noise. For simplicity, the force exerted on each blade is not distributed but concentrated at one point and the noise is evaluated by using Lowson' exact formula with a discussion of the physical meaning of each term in the formula. For a single point force rotating with various angular frequencies, we investigated the radiation characteristics and theoretically explained the physical behavior at near and far-field. By investigating the amplitude of acoustic pressure with various distances, we observed the different decreasing ratio at near- and far-field with the discussion of the effect of acceleration of angular frequency. Finally, the phenomenon that the noise level is reduced everywhere as the number of blade increases is explained with the suggestion of a noise reduction idea, the limitations of this study, and the future research topics.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.7 s.124
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• pp.596-604
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• 2007

This article investigates the effects of geometric configuration on the vibro-acoustic characteristics of in-plane vibration of a thick annular disc. Disc thickness and outer radius for a given inner radius are selected as independent variables having reasonable ranges. Variations in structural eigensolutions for radial modes are investigated using pre-developed analytical method. Based on these data, far-field sound pressure distributions due to the modal vibrations for a given geometry are also calculated using an analytical solution. Modal sound powers and radiation efficiencies are calculated from the far-field sound pressure distributions and vibratory velocity distributions on the radial surfaces. Based on the results explained above, the geometric configuration that minimizes modal sound radiations in a given frequency range is determined. Finally sound power and radiation efficiency spectra for a unit harmonic force from the selected geometric configuration are obtained from structural and acoustic modal data using the modal expansion technique. Multi-modal sound radiations of the optimized disc that are obtained using proposed analytical methods are confirmed with numerical results. Using the procedure introduced in this article, sound radiation due to in-plane modes within a specific frequency range can be minimized by the disc geometry modifications in a comprehensive and convenient manner.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.83-88
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• 1995

인간의 문화생활은 기계문명의 발달과정과 같이 성장해왔다. 기계문명의 발달에 따라 각종 산업기계의 사용은 점점 증가하게 되었고, 사회는 산업 기계 및 각종 소음으로 인한 피해도 더해가고 있다. 소음 문제를 해결하는 가장 최선의 방법은 소음원에서 방사되는 소음을 줄이는 것이다. Austria소재 Glaunach GmbH사와 기술 제휴하여 화력 발전소에서의 효과적인 소음 감소 방안으로 다음고 같은 공업용 소음기를 소개하고자 한다.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.443-446
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• 2004

추진기에 의한 소음은 선형 특성에 의한 반류 분포, 추진기 재질 및 유체 연동 등 다양한 주변 인자들에 의해 발생하여, 민수용 선박의 경우는 과도한 추진기 수중 방사 소음으로 해양 생태계 교란 및 선박 거주구역 내 과대 소음 형성의 주 요인이 된다. 더구나, 군사용 함정의 경우에는 추진기 유기 소음은 수중 방사소음의 형태로 전파되어 함정/무기 자체에 탑재된 음향센서의 기능을 저하시키는 영향을 줄 뿐 아니라, 원거리까지 전파되는 수중소음으로 인해 치명적인 자기 노출이 되어 적 함정에 의한 피탐 거리 증대라는 전술적 취약점을 초래하는 중요한 요소이다. 본 발표는 삼성 공동수조(SCAT)에서 이루어지는 추진기 유기 소음 측정에 대한 기술적 사항과 모형선-추진기 수조 시험을 통해 구해진 추진기 유기음향과 이론 및 경험식을 토대로 계산된 추진기 소음의 정량/정성적 비교를 통해, 추진기 설계 단계에서 소음수준 예측 도구로의 활용 가능성을 제시하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1060-1065
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• 2007

This paper summarizes a design procedure of radiated noise from engine blocks of marine engines. This air-borne noise is one of the significant noise contributors including the aeroacoustic noise due to intake and exhaust and the re-radiation due to structure-borne noise. Excitation forces by engine operations are evaluated taking into account the power generation mechanism from the burning process to the subsequence motion of internal parts; piston, connecting rod, and crank shaft. The acoustic transfer vector method is incorporated to effectively simulate the radiated noise field under the various operation conditions. A contribution analysis for the various excitations to the radiated noise is conducted. It is found that the firing pressure is the main source of the radiated noise, and so the structure of the cylinder can be modified to significantly reduce the radiated noise from the engine block.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.480-485
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• 2002

The overall noise reduction was compared in regard to the vibrational characteristics of floor impact noise in a multi story residential building which has several noise reduction treatments. The vibration through its structural elements such as wall, floor and ceiling and sound emitting were investigated for each insulation treatment. It was found that, in case of heavy-weight impact noise, the vibration energy is emitted mostly from ceiling, but for the light-weight impact noise, most of the energy comes through ceiling and walls. That is, the vibration of a ceiling is the main factor that determines the frequency characteristics of the transmitting noise to lower floors.