• Title/Summary/Keyword: Radiating Noise

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Development of indirect EFBEM for radiating noise analysis including underwater problems

  • Kwon, Hyun-Wung;Hong, Suk-Yoon;Song, Jee-Hun
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.5 no.3
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    • pp.392-403
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    • 2013
  • For the analysis of radiating noise problems in medium-to-high frequency ranges, the Energy Flow Boundary Element Method (EFBEM) was developed. EFBEM is the analysis technique that applies the Boundary Element Method (BEM) to Energy Flow Analysis (EFA). The fundamental solutions representing spherical wave property for radiating noise problems in open field and considering the free surface effect in underwater are developed. Also the directivity factor is developed to express wave's directivity patterns in medium-to-high frequency ranges. Indirect EFBEM by using fundamental solutions and fictitious source was applied to open field and underwater noise problems successfully. Through numerical applications, the acoustic energy density distributions due to vibration of a simple plate model and a sphere model were compared with those of commercial code, and the comparison showed good agreement in the level and pattern of the energy density distributions.

Structural Modification for Noise Reduction of the Blower Case in a Fuel Cell Passenger Car Based on the CAE Technology (승용연료전지 자동차용 블로워 케이스의 방사소음 저감을 위한 CAE 이용 구조변경에 관한 연구)

  • Song, Min-Keun;Lee, Sang-Kwon;Seo, Sang-Hoon
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.9
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    • pp.972-981
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    • 2008
  • The blower which is installed in a FCEV(fuel cell electric vehicle) may cause noise due to misalignment and unbalance of mechanical components that rotate at high speed. One of the key points in efforts to minimize the noise radiation from a blower is the knowledge of the main radiating component and the relation between the surface vibration of a blower and the sound pressure. In this research, the blower model is developed based on FEM(finite element method). FE(finite element) model is reliable by correlation of frequencies and MAC(modal assurance criterion) values between EMA(experimental modal analysis) and FEA(finite element analysis). This model is applied to predict the vibration of a blower by using inverse force identification method and predict the radiating noise by using BEM(boundary element method). Comparing the frequencies of resonance and those mode shapes between EMA and FEA, a structural modification of the FE model is evaluated for reducing the parameters of the blower noise.

Prediction Of Vibrating Panel's Radiating Noise By Transfer Path Analysis (전달경로해석법에 의한 진동하는 판넬의 방사 소음 예측)

  • Oh, Jae-Eung;Lee, Sun-Hun;Jeong, Un-Chang;Kim, Jin-Su;Lee, You-Yup
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2014.10a
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    • pp.292-293
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    • 2014
  • Transfer Path Analysis is technique predicting transmitted energy through each path. Using the Transfer Path Analysis, structure-borne noise and air-borne noise can be predicted from the system. In this study, however, the Transfer Path Analysis to target only the structure-borne noise due to the noise radiated from the vibrating panel was performed. Predicted noise by the Transfer Path Analysis and measured noise by the experiment were a high correlation. We confirmed the validity of the Transfer Path Analysis through the analysis of these results, showed how to apply the Transfer Path Analysis.

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Study on the relation between creep phenomena and radiating squeal noise about the railway (철도차량 곡선부 주행시 차륜에 작용하는 크립과 스킬소음 발생에 관한 고찰)

  • Kim, Beom-Soo;Kim, Sang-Soo;Kim, Kwan-Ju;Lee, Chan-Woo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.11a
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    • pp.61-64
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    • 2006
  • This paper presents experimental analysis of a friction-driven wheel responsible for generating wheel squeal. Squeal noise generating mechanism has been examined under the laboratory condition by the model rig. Creep characteristics and squeal noise were observed by varying relative velocity of the wheel with respect to the rail and friction coefficient. Computational radiating noise analysis was also performed based on the modal analysis and noise transfer function measurement of the object wheel.

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Vertical Space Analysis for Gradient Radiating Steel-tube Radiographic Image (경사조사(傾斜照射) 강판튜브 방사선 관측영상의 수직 방향 공간분석)

  • Hwang, Jung-Won;Hwang, Jae-Ho
    • Proceedings of the KIEE Conference
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    • 2007.04a
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    • pp.29-31
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    • 2007
  • In this paper we propose an directional analytic approach in image data space for X-ray image which is detected from the X-ray projection system. Such a radiographic nondestructive testing has long been used for steel-tube inspection and weld monitoring. The welded area and thickness of steel-tube are detected from gradient radiating mechanism based on the evaluation of biased X-ray source position. The welded area is an ellipse type on low contrast X-ray image including noise. Noise originates from most of elements of the system. such as shielding CCD camera, imaging screen, X-ray source, inspected object, electronic circuits and etc.. Projection incorrectness and noise influence on imaging quality is to be represented by vertical pixels' distribution. Space analysis due to vertical direction also shows the segmental possibility between regions by visual edge evaluation.

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Numerical Investigation on Radiation Characteristics of Noise Propagating through Asymmetry Aero-Intake (비대칭 공기흡입구를 통해 전파하는 소음의 방사특성에 관한 수치적 연구)

  • Park, Yong-Hwan;Kim, Min-Woo;Lee, Kyu-Ho;Lee, Soo-Gab
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.11a
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    • pp.1476-1481
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    • 2007
  • Numerical investigation on radiation characteristics of discrete frequency noise from asymmetry aero-intakes was carried out. The near-field predictions were obtained by solving the linearized Euler equations with computational aeroacoustic techniques consisting of high order finite difference scheme, non-reflecting boundary conditions, oversetgrid techniques. For the prediction of far-field directivity pattern, the Kirchhoff integral method was applied. By comparing the directivities of noise radiating from the scarf and the scoop aero-intakes with that from an axisymmetric aero-intake, it is shown that noise reduction at downward peak radiation angle can be achieved. The scattering of the radiating acoustic wave by background mean flow shifts the peak lobe radiation angle toward ground and increases the amplitude of the acoustic pressure compared with the cases without mean flow effect.

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Structure-borne Noise Reduction of Plate using bead (비드를 이용한 평판의 구조소음 저감)

  • Kim, Ho-San;Sim, Hyoun-Jin;Kang, Kwi-Hyun;Jung, Dong-Hyun;Oh, Jae-Eung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2007.05a
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    • pp.269-274
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    • 2007
  • With the importance of comfortable environment, research about noise reduction of construction is consisting much. If construction receives the input force, noise will be generated thereby. We must predict vibration and noise characteristic to reduce structured borne noise, and construction which become a basis of such research is plate. In order to predict the radiating noise from the vibrating surface. It is required to know the velocity distribution of vibration surface exactly. It is good to use bead for reducing vibration and noise of plate. In this study, we have analyzed structure-borne noise of plate with bead and compare with plate that there is no bead about equal exciting force.

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The Performance Comparison of Active Noise Controller With Phase Difference (위상차에 따른 소음 제거기의 성능 비교)

  • 최창권;조병모
    • Proceedings of the IEEK Conference
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    • 1999.06a
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    • pp.695-698
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    • 1999
  • Passive noise reduction is a classical approach to attenuate industrial noise. But Active noise cancellation has several advantages over the passive noise cancellation. Such a system offers a better low frequency performance with a smaller and lighter system. This paper presents an active closed loop control system which consists of an controller for inverting and compensating the phase delay, an microphone for picking up the external noise, and loudspeaker for radiating the acoustic anti-phase signal to reduce external noise. The noise in the phase delay covered from 80$^{\circ}$ to 270$^{\circ}$ tends to be reduced. The degree of noise cancellation obtainable with this system reaches value about 17㏈.

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An Experimental Study for Noise Reduction of the Cross-Flow Fan of the Room Air-Conditioners

  • Koo, Hyoung-Mo
    • International Journal of Air-Conditioning and Refrigeration
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    • v.8 no.2
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    • pp.89-100
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    • 2000
  • Present study explains some experimental results on the aerodynamic noise of the cross-flow fan usually installed in the indoor unit of the room air-conditioners and provides a simple reduction method of radiating sound to decrease the total noise level. The spectra of the noise of the cross-flow fan were analyzed by the spectral decomposition method to characterize the generated sound. The unsteady fluctuating flow field was also measured using the I-type hot-wire probe. Comparing the spectral characteristics of the sound and the flow velocity, a useful noise reduction method was proposed, which bounds the region with a fence where the flow fluctuations were noticeably changed in the same fashion as the source spectral distribution functions vary. To validate the proposed method for reducing noise generated by the cross-flow fan, the sound pressure levels of the cross-flow fan system were compared with and without the bounding fence for various flow rates.

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An experimental study for noise reduction of the cross-flow fan of the room air-conditioners (에어컨용 직교류홴의 저소음화를 위한 실험적 연구)

  • 구형모
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.6
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    • pp.871-879
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    • 1999
  • Present study explains some experimental results on the aerodynamic noise of the cross-flow fan usually installed in the indoor unit of the room air-conditioners and provides a simple reduction method of radiating sound to decrease the total noise level. The spectrums of the noise of the cross-flow fan were analyzed by the spectral decomposition method to characterize the generated sound. The unsteady fluctuating flow field was also measured using the I-type hot-wire probe. Comparing the spectral characteristics of the sound and the flow velocity, a useful noise reduction method was proposed which bounds the region with a fence where the flow fluctuations were noticeably changed in the same fashion as the source spectral distribution functions vary. To validate the proposed method for reducing noise generated by the cross-flow fan, the sound pressure levels of the cross-flow fan system were compared of the experimental rig with and without the bounding fence for various flow rates.

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