• Title, Summary, Keyword: Acoustic Power Spectrum

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A Study on the Spectrum Analyzing of Internal Leak in Valve for Power Plant Using Acoustic Emission Method (음향방출법에 의한 발전용 밸브내부 누설의 스펙트럼분석 연구)

  • Lee, Sang-Guk;Lee, Sun-Ki;Lee, Jun-Shin;Sohn, Seok-Man
    • Proceedings of the KSME Conference
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    • pp.694-699
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    • 2004
  • The purpose of this study is to estimate the availability of acoustic emission method to the internal leak of the valves at nuclear power plants. The acoustic emission method was applied to the valves at the site, and the background noise was measured for the abnormal plant condition. From the comparison of the background noise data with the experimental results as to relation between leak flow and acoustic signal, the minimum leak flow rates that can be detected by acoustic signal was suggested. When the background levels are higher than the acoustic signal, the method described below was considered that the analysis the remainder among the background noise frequency spectrum and the acoustic signal spectrum become a very useful leak detection method. A few experimental examples of the spectrum analysis that varied the background noise characteristic were given.

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Prediction of acoustic power radiated from an airfoil with thickness in turbulent flow (난류 유동장 내 두께를 가지는 단일 에어포일의 음향파워 예측)

  • Kim, Daehwan;Cheong, Cheolung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.353-358
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    • 2013
  • Present paper deals with turbulence-airfoil interaction noise and mainly investigates the effects of airfoil thickness on the broadband noise spectrum. The acoustic power radiation from an airfoil is predicted using high-order time-domain method, which is based on the computational aeroacoustic technique solving the linear Euler equations. The homogeneous and isotropic turbulence is generated by utilizing the synthetic turbulence modeling based on random particle method. The airfoils taken into consideration are a flat-plate and a NACA0012 airfoil aligned with uniform mean flow. The effects of airfoil thickness on the radiated inflow turbulence noise are investigated by comparing acoustic power spectrum predicted for each airfoil. The comparison of acoustic power spectrum reveals that the airfoil thickness significantly contributes the high frequency noise reduction.

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A Study on the Frequency Analyzing of Leak Evaluation m Valve for Power Plant Using AE (AE법에 의한 발전용 밸브누설평가를 위한 주파수분석 연구)

  • LEE SANG-GUK
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • pp.360-364
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    • 2004
  • The objective of this study is to estimate the feasibility of acoustic emission method Jar the internal leak from the valves in nuclear power plants. The acoustic emission method was applied to the valves at the site, and the background noise was measured for the abnormal plant condition. From the comparison of background noise data with the experimental results as to relation between leak flow and acoustic signal, the minimum leak flow rates that am be detected by acoustic signal was suggested. When the background noise level are higher than the acoustic signal, the method described below was considered that the analysis the remainder among the background noise frequency spectrum and the acoustic signal spectrum.

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Computation of Broadband Noise of a 2-B Flat-airfoil Cascade Subject to Ingested Turbulence (난류 와류의 입사에 의한 이차원 평판 에어포일 캐스케이드의 광대역 소음장의 계산)

  • Cheong, Cheolung;Joseph Phillip;Lee, Soogab
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.15 no.6
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    • pp.687-696
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    • 2005
  • Acoustic power spectrum of the upstream and downstream sound field due to an isotropic frozen turbulent gust impinging on a cascade of flat plate airfoils are computed by using a analytic formulation derived from Smith's method, and Whitehead's LINSUB codes. A parametric study of the effects on sound power of the number of blades and turbulence length scale is performed with an emphasis on analyzing the characteristics of sound power spectrum. Through the comparison of the computed results of sound power, it is found that acoustic power spectrum from the 2-D cascade subject to a ingested turbulence can be categorized into two distinct regions. one is lower frequency region where some spectral components of turbulence do not contribute to the cut-on acoustic modes and therefore the effect of the cascade geometry is more dominant ; the other is higher frequency region where all of spectral components of turbulence make contributions to cut-on acoustic modes and thus acoustic power is approximately proportional to the blade number.

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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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.

Acoustic Impulse Method with Neural Network for Detection of Cracks in Eggshell (음향충격법과 인공신경망에 의한 파란 검출)

  • 최완규;조한근;백진하;장영창
    • Journal of Biosystems Engineering
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    • v.23 no.6
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    • pp.621-628
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    • 1998
  • In order to develop an inspection algorithm for an automatic eggshell inspection system, acoustic impulse response with neural network method was studied. An improved error backpropagation algorithm was selected as a loaming rule of neural network, and three layer network was chosen for the neural network architecture. Acoustic signals in time domain and theirs power spectrum were studied as the input to the neural network. The classification feasibility and success rate were investigated in terms of statistical analysis and neural network approach. As a result, the success rate was 95% with the statistical model having five independent variables. Among the neural network models studied, the power spectrum of acoustic signal as the input with 64 input neurons and the two impact data showed the success rate of 95.5% which was slightly higher than of statistical analysis.

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Factors Affecting Acoustic Responses of Egg Shell (난각의 음향반응에 영향을 주는 인자)

  • 조한근;최완규
    • Journal of Biosystems Engineering
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    • v.22 no.1
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    • pp.41-48
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    • 1997
  • A nondestructive quality inspection technique using acoustic impulse response method was studied to investigate the feasibility of egg shell inspection. An experimental system was built to generate impact force, to measure the response signal and to analyze the frequency spectrum. This system includes an impulse generating unit, an egg holding seat, a microphone with preamplifier, and a digital oscilloscope connected to Personal Computer by RS-232C interface. The factors such as impulse generating method, egg holding method, and sensor location were evaluated by analyzing the power spectrum density of the measured signal. The results obtained are summarized as follows : 1. From the sampled eggs, the proper conditions for detecting damaged eggs were found as followings; ceramic for the impact ball material, rubber for egg seat material, 20 degrees for an impact angle of pendulum, 10mm for the distance between egg and sensor, the sharp side for impacting part, and 180 degrees for the location of sensor. 2. Examination of the Fourier transformed analysis in beth normal and damaged eggs revealed that those factors such as the resonant frequency, a number of peak frequencies and the magnitude of power spectrum were important to detect damaged eggs.

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Application of Non-linear Acoustic Effect for Evaluation of Degradation of 2.25Cr-1Mo Steel (2.25Cr-1Mo 강의 열화도 평가를 위한 비선형 음향효과 응용법)

  • Choi, Y.H.;Jhang, K.Y.;Park, I.K.;Kim, H.M.
    • Journal of the Korean Society for Nondestructive Testing
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    • v.22 no.2
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    • pp.170-176
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    • 2002
  • Nonlinear acoustic effect has been considered as an effective tool for the evaluation of material degradation. In this paper, the applicability of nonlinear acoustic effect to the evaluation of degraded 2.25Cr-1Mo steel is investigated. Firstly, artificial aging was performed to simulate the microstructural degradation in 2.25Cr-1Mo steel arising from long time exposure at $540^{\circ}C$. Secondly, ultrasonic nonlinear parameter was quantitatively measured by bi-spectrum and power spectrum. Nonlinear acoustic parameter from bi-spectrum was found to be clearly sensitive to the aging time.

The Electronic Ballast Design of Acoustic Resonance Free and Transient Over Current Limit for High Power MHL (음향 공명 제거 및 과도 상태 전류를 제한시킨 고출력 메탈 헬라이드 램프용 전자식 안정기 설계)

  • Kim, Ki-Nam;Park, Jong-Yun;Choi, Young-Min
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.59 no.5
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    • pp.904-911
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    • 2010
  • This paper presents the design of acoustic resonance free and over current limit during transient state consideration electronic ballast for 1.5kW Metal-Halide Lamp(MHL) that employs frequency modulation (FM) technique. The proposed ballast consists of a Full-Bridge(FB) rectifier, a passive power factor correction (PFC) circuit, a full-bridge inverter, an ignitor using LC resonance and a control circuit for frequency modulation. The frequency modulation technique is the most effective solution to eliminate acoustic resonance among other technique. It spreads power spectrum of lamp to reduce the supplied power spectrum under the energy level of eigen-value frequency. Moreover, the proposed ballast is simple and cost effective above conventional ballast. A new PFC circuit is proposed which combines with LCD type and PCSR filter. A new PFC circuit has higher PF and lower THD than conventional LCD type and secure high reliability. Finally, to protected switching components in transient state, the surge current into ballast is limited by increase the switching frequency. Performance of the proposed ballast was validated through computer simulation using Pspice, experimentation and by applying it to an electronic ballast for a prototype 1.5kW MHL.