• Title, Summary, Keyword: Acoustic noise

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Acoustic resonance by Inserting Anti-noise Baffle in the Tube Bank of Boiler of a Large Fossil Power Plant (대형석탄화력발전용 보일러 관군의 Anti-Noise Baffle 설치에 따른 음향공진)

  • Bang, Kyung-Bo;Kim, Cheol-Hong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.178-183
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    • 2004
  • This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a large fossil power plant. The phenomena of acoustic resonance may arise when the vortex shedding frequency coincides with the acoustic natural frequency. In this system dominant frequency of vibration and noise was 37.5Hz. The $3^{rd}$ acoustic natural frequency calculated was 37.2 Hz. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}20%$, acoustic resonance could occur. If system is the state of acoustic resonance, vibration and noise become large. In order to prevent acoustic resonance, anti-noise baffle should be installed in the tube bank. In the case of installing baffle, we should consider the number of baffle and the effect of acoustic mode due to baffle extension length. To do this, we did acoustic mode analysis. After installing anti-noise baffle, acoustic resonance was disappeared and vibration magnitude and noise level was reduced dramatically.

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The numerical analysis of heavy-weight impact noise for an apartment houses considering acoustic mode (Acoustic mode 를 고려한 공동주택 중량충격음 소음해석)

  • Mun, Dae-Ho;Hwang, Jae-Seung;Park, Hong-Gun;Hong, Geon-Ho;Im, Ju-Hyeuk
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.394-402
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    • 2009
  • To investigate the heavy-weight impact noise of apartment houses, numerical analysis was performed. The analysis acoustic pressure consider acoustic mode by finite element method. The variables considered effecting on the acoustic pressure are the Acoustic mode, acoustic damping, and the impulse load. The heavy-weight impact noise is a changeable value in the room. Since the most part of the frequency component of heavy-weight impact noise has low frequency. The noise in low frequency is related to the vibration of structure, the reflection of acoustic wave caused by wall and the standing wave called by acoustic mode. The prediction by the numerical analysis was verified with test result of the heavy weight-impact noise at apartment houses.

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Structural noise mitigation for viaduct box girder using acoustic modal contribution analysis

  • Liu, Linya;Qin, Jialiang;Zhou, Yun-Lai;Xi, Rui;Peng, Siyuan
    • Structural Engineering and Mechanics
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    • v.72 no.4
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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.

Identification of Noise Source of the HVAC Using Complex Acoustic Intensity Method (복소음향인텐시티법을 이용한 HVAC의 소음원 검출)

  • Yang, Jeong-Jik;Lee, Dong-Ju
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.20 no.11
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    • pp.1089-1096
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    • 2010
  • 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 measurement and 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. As an industrial application, the complex acoustic intensity method is applied to HVAC to identify sound radiation characteristics in the near field. Experimental complex acoustic intensity method was applied to HVAC, it is possible to identify noise sources in complicated sound field characteristics which noise sources are related with each other, and certificate the validity of complex acoustic intensity. Especially, it can be seen that complex acoustic intensity method using both of active and reactive intensity is vital in devising a strategy for identification of noise. Also, the vector flow of acoustic intensity was investigated to identify sound intensity distributions and energy flow in the near field of HVAC.

The Study for Vibro-acoustic Noise Analysis in the Fuselage of Regional Turboprop Airplane (중형항공기 동체 소음해석 기법 연구)

  • Park, Illkyung;Kim, Sungjoon;Jung, Jinduck
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.20 no.3
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    • pp.44-50
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    • 2012
  • The noise reduction is important one of considerations in the process of a civil aircraft development program. External noise sources are classified into an air-born source and a structure-born source. Among these noise sources, the most affected noise source into a cabin is the air-born noise source from an engine or propeller. The external noise is transmitted into the cabin through the fuselage structure of airplane which are composed of an fuselage structure, an interior trim panel and an acoustic insulation layer between an fuselage structure and an interior trim panel. Therefore, appropriate fuselage structure and acoustic insulation layer is very important to reduce the internal noise level. In this paper, the vibro-acoustic coupled analysis of the cabin noise of the 80~90 seats regional turboprop aircraft is carried out to validate the acoustic analysis method using Direct BEM and FEM. The sound pressure level onto the fuselage skin is acquired by fan-source noise analysis using BEM, and which sound pressure is used as acoustic noise source in vibro-acoustic noise analysis for cabin noise analysis using FEM.

Prediction vehicle interior noise using Acoustic Transfer Function (Acoustic Transfer Function을 이용한 실차 실내 소음 예측)

  • Koh, Sung-Gyoo;Shin, Han-Seung;Cho, Whan-Chul
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.534-537
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    • 2011
  • This Paper present prediction Vehicle Interior Noise using ATF(Acoustic Transfer Function) and engine radiated sound power. This is useful tool to qualifying the effectiveness of Air-borne noise Path. Furthermore This method provide acoustic package performance of the vehicle and able to prepare frequency band to same segment or benchmarking vehicle.

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An acoustic feature [noise] in the sound pattern of Korean and other languages (소리체제에서 음향 자질[noise]: 한국어와 기타 언어들에서의 한 예증)

  • Rhee, Seok-Chae
    • Speech Sciences
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    • v.6
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    • pp.103-117
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    • 1999
  • This paper suggests that the onset-coda asymmetry found in languages like Korean and others should be dealt with in terms of one acoustic feature rather than other articulatory features, claiming that the acoustic feature involved here is [noise], i.e., 'aperiodic waveform energy'. It determines the structural well-formedness of the languages in question whether a coda ends in [noise] or not, regardless of the intensity, the frequency, and the time duration of the [noise]. Fricatives, affricates, aspirated stops, tense stops, and released stops are all disallowed in the coda position due to the acoustic feature [noise] they, commonly end with if they were, posited in the coda. The proposal implies that the three seemingly separate prohibitions of consonants in the coda position -- i) no fricatives/affricates, ii) no aspirated/tense stops, and iii) no released stops -- are directly correlated with each other. Incorporation of the one acoustic feature [noise] in the feature theory enables us to see that the aspects of onset-coda asymmetry are derived from one single source: ban, of [noise] in the coda.

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The Influence of Design Factors of Sonar Acoustic Window on Transfer Function of Self Noise due to Turbulent Boundary Layer (소나 음향창의 설계 인자가 난류 유동 유기 자체 소음의 전달 함수에 미치는 영향 해석)

  • Shin, Ku-Kyun;Seo, Youngsoo;Kang, Myengwhan;Jeon, Jaejin
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.23 no.1
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    • pp.56-64
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    • 2013
  • Turbulent boundary layer noise is already a significant contributor to sonar self noise. For developing acoustic window of sonar system to reduce self noise, a parametric study of design factors of acoustic window is presented. Distance of sensor array from acoustic window, materials of acoustic window and characteristics of damping layer are studied as design factors to influence in the characteristics of the transfer function of self noise. As the result, these design factors make change the characteristics of transfer function slightly. Among design factors the location of sensor array is most important parameter in the self noise reduction

Characteristics of Modal Acoustic Power of Broadband Noise by Interaction of a Cascade of Flat-plate Airfoils with Inflow Turbulence (평판 에어포일 캐스케이드와 입사 난류의 상호작용에 의한 광대역 소음의 모달 음향 파워 특성)

  • Cheong, Cheol-Ung;Jurdic, Vincent;Joseph, Phillip
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.1
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    • pp.61-70
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    • 2008
  • This paper investigates the modal acoustic power by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. Basic formulation for the acoustic power upstream and downstream is based on the analytical theory of Smith and its generalization due to Cheong et al. The acoustic power spectrum has been expressed as the sum of cut-on acoustic modes, whose modal power is the product of three terms: a turbulence series, an upstream or downstream power factor and an upstream or downstream acoustic response function. The effect of these terms in the modal acoustic power has been examined. For isotropic turbulence gust, the turbulent series are only reducing factor of the modal acoustic power. The power factor tends to reduce the modal acoustic power in the upstream direction, although the power factor is liable to increase the modal acoustic power in the downstream direction. The modes close to cut-off are decreasing strongly, especially in the downstream direction. Therefore the modes close to cut-off don't contribute highly to the radiated acoustic power in the downstream direction, although the modal acoustic pressure is high for these modes.

Modal acoustic power of broadband noise by interaction of a cascade of flat-plate airfoils with inflow turbulence (평판 에어포일 캐스케이드와 입사 난류의 상호작용에 의한 광대역 소음의 모달 음향 파워)

  • Cheong, Cheol-Ung;Jurdic, Vincent;Joseph, Phillip
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.1467-1475
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    • 2007
  • This paper investigates the modal acoustic power by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. Basic formulation for the acoustic power upstream and downstream is based on the analytical theory of Smith and its generalization due to Cheong et al. The acoustic power spectrum has been expressed as the sum of cut-on acoustic modes, whose modal power is the product of three terms: a turbulence series, an upstream or downstream power factor and an upstream or downstream acoustic response function. The effect of these terms in the modal acoustic power has been examined. For isotropic turbulence gust, the turbulent series are only reducing factor of the modal acoustic power. The power factor tends to reduce the modal acoustic power in the upstream direction, although the power factor is liable to increase the modal acoustic power in the downstream direction. The modes close to cut-off are decreasing strongly, especially in the downstream direction. Therefore the modes close to cut-off don't contribute highly to the radiated acoustic power in the downstream direction, although the modal acoustic pressure is high for these modes.

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