• Title, Summary, Keyword: Acoustic

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FEM acoustic modal analysis due to location of acoustic baffles to avoid acoustic resonance in the tube bank of boiler for power plant (보일러 튜브군의 음향공진 회피를 위한 음향배플의 위치에 따른 FEM 음향모드해석)

  • Ahn, Sung-Jong;Ju, Young-Ho;Kim, Cheol-Hong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.150-154
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    • 2012
  • A flow induced mechanical vibration and acoustic resonance should be considered at design stage because they are mainly occurred in the tube bank of boiler. Acoustic resonance is occurred when the vortex shedding frequency of tube bank coincides with the acoustic natural frequency of the cavity. Effective solution to avoid acoustic resonance is installing acoustic baffles in the tube banks parallelly inside of the flow cavity. Thus, location and number of acoustic baffles should be exactly calculated to eliminate the acoustic resonance. This paper presents case study of acoustic resonance due to inappropriate number and location of acoustic baffles. Measured frequency and mode in the study is verified by FEM acoustic modal analysis. The number and location of acoustic baffles to avoid acoustic resonance are calculated by using FEM acoustic modal analysis.

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Numerical Analysis of Acoustic Behavior in Gas Turbine Combustor with Acoustic Resonator (음향공명기가 장착된 가스터빈 연소실의 음향장 해석)

  • Park, I-Sun;Sohn, Chae-Hoon
    • Proceedings of the KSME Conference
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    • pp.1110-1115
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    • 2004
  • Acoustic behavior in gas turbine combustor with acoustic resonator is investigated numerically by adopting linear acoustic analysis. Helmholtz-type resonator is employed as acoustic resonator to suppress acoustic instability passively. The tuning frequency of acoustic resonator is adjusted by varying its length. Through harmonic analysis, acoustic-pressure responses of chamber to acoustic excitation are obtained and the resonant acoustic modes are identified. Acoustic damping effect of acoustic resonator is quantified by damping factor. As the tuning frequency of acoustic resonator approaches the target frequency of the resonant mode to be suppressed, mode split from the original resonant mode to lower and upper modes appears and thereby complex patterns of acoustic responses show up. Considering mode split and damping effect as a function of tuning frequency, it is desirable to make acoustic resonator tuned to broad-band frequencies near the maximum frequency of those of the possible upper modes.

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A Numerical Study on Acoustic Behavior in Gas Turbine Combustor with Acoustic Resonator (음향공명기가 장착된 가스터빈 연소실의 음향장 해석)

  • Park, I-Sun;Sohn, Chae-Hoon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.1
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    • pp.95-102
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    • 2005
  • Acoustic behavior in gas turbine combustor with acoustic resonator is investigated numerically by adopting linear acoustic analysis. Helmholtz-type resonator is employed as acoustic resonator to suppress acoustic instability passively. The tuning frequency of acoustic resonator is adjusted by varying its length. Through harmonic analysis, acoustic-pressure responses of chamber to acoustic excitation are obtained and the resonant acoustic modes are identified. Acoustic damping effect of acoustic resonator is quantified by damping factor. As the tuning frequency of acoustic resonator approaches the target frequency of the resonant mode to be suppressed. mode split from the original resonant mode to lower and upper modes appears and thereby complex patterns of acoustic responses show up. Considering mode split and damping effect as a function of tuning frequency, it is desirable to make acoustic resonator tuned to broad-band frequencies near the maximum frequency of those of the possible upper modes.

Acoustic resonance by length of acoustic baffle at Finned Tube bank (핀-튜브군에서 배플 길이에 따른 음향공진)

  • 방경보;류제욱
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.98-103
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    • 2003
  • This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a HRSG. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At this tube bank, dominant frequencies of vibration in this system were 43.5, 67.5㎐. The 3$\^$rd/ acoustic natural frequency calculated was 68.5㎐. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}$20%, acoustic resonance could occur. In this system, in order to prevent acoustic resonance, acoustic baffle was installed in the tube bank before operating. But acoustic resonance occurred. So, we evaluate the effect of acoustic mode due to baffle extension length. After investigating, we did revise acoustic baffle to eliminate acoustic resonance effectively.

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Numerical Analysis of Acoustic Characteristics in Gas Turbine Combustor with Spatial Non-homogeneity

  • Sohn, Chae-Hoon;Cho, Han-Chang
    • Journal of Mechanical Science and Technology
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    • v.18 no.8
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    • pp.1461-1469
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    • 2004
  • Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by a linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analyses are conducted in the combustors without and with acoustic resonator, which is one of the acoustic-damping devices or combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in good agreement with the measurement data. In this regard. the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. From the numerical results for the combustor with present acoustic resonators installed, the acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity. It is found that the resonators with present specifications are not optimized and thus, the improved specification or design is required.

Analysis of Resonance Characteristics of Bulk Acoustic Resonator with Acoustic Bragg Reflector for Biosensor Development (바이오센서 개발을 위한 음향 브래그 반사층을 가지는 체적탄성파 공진기의 공진특성 분석)

  • Kim, Hee-Young;Kim, Ki-Bok;Ha, Tae-Hoon;Kim, Yong-Il;Lee, Jin-Min;Kim, Man-Soo
    • Journal of Biosystems Engineering
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    • v.34 no.4
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    • pp.260-268
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    • 2009
  • As a basic study to develop a high sensitive biosensor using film bulk acoustic resonator, the mathematical model for analyzing the resonance characteristics of bulk acoustic resonator with acoustic Bragg reflectors was investigated. The simulation results due to the number of acoustic Bragg reflectors with low and high acoustic impedance materials were compared with the experimental results for 1, 2.25 and 5 MHz of PZT based bulk acoustic resonators with various acoustic Bragg reflectors. At the fabricated bulk acoustic resonator with an odd number of acoustic Bragg reflectors, low and high acoustic impedance materials in sequence under the bottom electrode showed better resonance characteristics than even number of acoustic Bragg reflectors. The changes of resonance frequencies due to the increase of number of acoustic Bragg reflectors by simulation and experiment, respectively showed approximately similar tendency but some differences in input impedance between the experiment and simulation were found. The derived mathematical model for describing the resonance characteristics of the bulk acoustic resonator with acoustic Bragg reflector will be available for analyzing the design parameters for development of biosensor using bulk acoustic resonator.

Development of Acoustic Substructure Synthesis Method using Component Mode Synthesis Method (모드합성법을 이용한 음향부분구조합성법의 개발)

  • 고상철;조용구;오재응;김준태;김진오
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.118-123
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    • 1996
  • The purpose of this study is to develop acoustic substructure synthesis method that can be applied to acoustic modal analysis of complex acoustic systems. Acoustic modal analysis method to be introduced here is a method that analyze acoustic natural mode shape of the complex acoustic system by the principle of CMS(component mode synthesis method). This paper describes the acoustic modal analysis of the acoustic finite element model of simple expansion pipe by acoustic substructure synthesis method. The results of acoustic modal analysis analyzed by Acoustic substructure synthesis method and the results, by FEM(finite element method) shows good agreement.

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Experimental Study of the Role of Gas-Liquid Scheme Injector as an Acoustic Resonator in a Combustion Chamber

  • Kim Hak-Soon;Sohn Chae-Hoon
    • Journal of Mechanical Science and Technology
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    • v.20 no.6
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    • pp.896-904
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    • 2006
  • In a liquid rocket engine, the role of gas-liquid scheme injector as an acoustic resonator or absorber is studied experimentally for combustion stability by adopting linear acoustic test. The acoustic-pressure signals or responses from the chamber are monitored by acoustic amplitude. Acoustic behavior in a rocket combustor with a single injector is investigated and the acoustic-damping effect of the injector is evaluated for cold condition by the quantitative parameter of damping factor as a function of injector length. From the experimental data, it is found that the injector can play a significant role in acoustic damping when it is tuned finely. The optimum tuning-length of the injector to maximize the damping capacity is near half of a full wavelength of the first longitudinal overtone mode traveling in the injector with the acoustic frequency intended for damping in the chamber. When the injector has large diameter, the phenomenon of the mode split is observed near the optimum injector length and thereby, the acoustic-damping effect of the tuned injectors can be degraded.

A Study on Correlation Between Pressure Variations and Augmentation of Heat Transfer in Acoustic Fields

  • Oh, Yool-Kwon;Yang, Ho-Dong
    • Journal of Mechanical Science and Technology
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    • v.18 no.9
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    • pp.1630-1639
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    • 2004
  • The present paper investigated the correlation between the acoustic pressure variations and the augmentation of heat transfer in the ultrasonic induced acoustic fields. The augmentation ratios of heat transfer coefficient were experimentally measured and were compared with the profile of the pressure distribution in the acoustic fields predicted by numerical analysis. For numerical analysis, a coupled finite element-boundary element method (coupled FE-BEM) was applied. The results of the present study reveal that the acoustic pressure is higher near two ultrasonic transducers than other points where no ultrasonic transducer was installed. The augmentation trend of heat transfer is similar with the profile of the acoustic pressure distribution. In other words, as the acoustic pressure increases, the higher augmentation ratio of heat transfer is obtained. Numerical and experimental studies clearly show that the acoustic pressure variations are closely related to the augmentation of heat transfer in the acoustic fields.

Application of Substructure Synthesis Method for Analysis of Acoustic System (음향계의 해석을 위한 부분구조합성법의 적용)

  • 오재응;고상철;조용구
    • Journal of KSNVE
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    • v.7 no.5
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    • pp.737-746
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    • 1997
  • The substructure synthesis method is used for making it easy to analyze vibration systems generally in vibration field. In the past, this method has been to be used mainly because of shortage of computer memory and CPU time. But recently this method is used for analyzing complex structure or identifying the characteristics of systems precisely. The purpose of this study is to develop acoustic substructure synthesis method that can be applied to acoustic modal analysis of complex acoustic systems. Acoustic modal analysis method to be introduced here is a method that analyze acoustic natural mode shape of the complex acoustic system by the principle of CMS(component mode synthesis method). This paper describes the acoustic modal analysis of the acoustic finite element model of simple expansion pipe by acoustic substructure synthesis method. The resutls of acoustic modal analysis analyzed by Acoustic substructure synthesis method and the results by FEM(finite element method) shows good agreement.

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