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  • Title/Summary/Keyword: 수치진동

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Passive Control System for Mitigation of Cable Vibration in Cable-Stayed Bridges (사장교의 케이블 진동저감을 위한 수동 제어시스템)

  • Hwang, Inho;Lee, Jong Seh
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.5A
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    • pp.881-885
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    • 2006
  • Rain-wind induced cable vibration can cause serious problems in cable-stayed bridges. Externally attached dampers have been used to provide an effective means to suppress the vibration of relatively short stay-cables. For very long stay-cables, however, such damper systems are rendered ineffective, as the dampers need to be attached near the end of cables for aesthetic reasons. This paper investigates a new control system to mitigate the cable vibration. The proposed control system which consists of a laminated rubber bearing and an internal damper may be installed inside of the cable anchorage. A simple analytical model of the cable-damper system is developed first based on the taut string representation of the cable. The response of a cable with the proposed control system is obtained and then compared to those of the cable with and without an external passive damper. The proposed stay-cable vibration control system is shown to perform better than the optimal passive viscous damper, thereby demonstrating its applicability in large cable-stayed bridges for mitigation of rain-wind induced vibration of stay-cables.

Analysis of relative contribution of machinery-induced vibration/flow-induced vibration to noise radiation from compressor discharging piping system in air-conditioner outdoor unit (에어컨 실외기 압축기 배기 배관계의 기기 기인 진동/유동 기인 진동의 방사소음에 대한 상대적 기여도 분석)

  • Sangheon Lee;Cheolung Cheong;Jinhyung Park;Jangwoo Lee
    • The Journal of the Acoustical Society of Korea
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    • v.43 no.1
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    • pp.122-130
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    • 2024
  • Vibration of compressor in the air-conditioner outdoor unit have known to be main noise source radiated from outdoor unit. However, as the operating speed of compressor increase, the relative contribution of flow induced vibration and noise is also increase. In this paper, the numerical method was established to predict fluid-borne noise from compressor discharging pipe of air-conditioner outdoor unit. In this step, numerical result was compared to experimental one to verify numerical method. Additionally, the effects of pressure pulsation of compressor and compressor vibration into radiated noise were investigated in frequency domain. It was confirmed that the compressor vibration contributed to the low frequency band, while the pressure pulsation dose to the high frequency band.

Analysis of Sound Attenuation by Chambers in Duct Systems by the Finite Element Method (유한요소법에 의한 소음기의 감음특성해석)

  • 최석주
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1991.04a
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    • pp.23-27
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    • 1991
  • 각종 홀 (음악홀, 극장, 사무실건물)의 공조 덕트계에는 미로형소음챔버가 설 치되는 경우가 많다. 이러한 소음장치를 건물내부에 설치하는 경우에는 건물 설계단계에서부터 소음챔버로 인한 감음양(투과손실 : Transmission Loss)의 예측계산이 중요하다. 그렇지만, 일반적인 소음장치는 그 형상이나 내표면의 흡음조건이 아주 복잡하기 때문에, 현단계에서는 간단한 이론만으로 투과손 실예측이 거의 불가능하다. 지금까지 이 문제에 대해서 유한요소법(Finite Element Method : FEM)을 이용해 검토한 예가 종종 소개되었으나, 대부분 소음챔버의 입구와 출구에서의 임의의 점에 대한 음압비를 투과손실로서 구 하고 있다. 그러나, 소음기자체의 실질적인 투과손실특성을 알기 위해서는 소음기의 입력 파워에 대한 출력파워의 비로서 구하지 않으면 안된다. 따라 서, 본 연구에서는 유한요소법에 의한 복소음향인텐시티(Complex sound intensity)의 수치계산법을 각종소음기 (팽창형, 미로형)의 투과손실해석에 적 용하기 위하여 이론적인 면에서 고찰했으며, 프로그램도 개발하여 모델해석 에 적용하였다. 또한, 위에서 언급된 수치해석법의 타당성의 검증을 위하여, 측정에 의한 투과손실예측방법으로서 크로스스펙트럼(Cross Spectrum)법에 의한 음향인텐시티계측법의 이용에 대해서 이론적으로 고찰했으며, 그 이론 을 기초로 한 축척 모형실험을 병행하였다.

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Critical Loads of Tapered Cantilever Columns with a Tip Mass (자유단 집중질량을 갖는 변단면 캔틸레버 기둥의 임계하중)

  • Jeong, Jin Seob;Lee, Byoung Koo;Kim, Gwon Sik;Kim, Jong Ung
    • Journal of Korean Society of Steel Construction
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    • v.17 no.6 s.79
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    • pp.699-705
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    • 2005
  • This paper investigates critical loads of tapered cantilever columns with a tip mass, subjected to a follower force. The linearly tapered solid rectangular cross-sections are adopted as the column taper. The differential equation governing free vibrations of such columns, also called Beck's columns, is derived using the Bernoulli-Euler beam theory. Both divergence and flutter critical loads are calculated from the load-frequency curves that are obtained by solving the differential equation. The critical loads are presented as functions of various non-dimensional system parameters, namely, the taper type, the subtangential parameter, and the mass ratio.

Direct Numerical Simulation of the Flow Past an Oscillating Circular Cylinder (진동하는 원주주위 유동의 직접수치해석)

  • Kang S. J.;Tanahashi M.;Miyauchi T.;Lee Y. H.
    • Journal of computational fluids engineering
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    • v.6 no.4
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    • pp.26-34
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    • 2001
  • The flow past a circular cylinder forced to vibrate transversely is numerically simulated by solving the two-dimensional Navier-Stokes equations modified by the vibration velocity of a circular cylinder at a Reynolds number of 164. The higher-order finite difference scheme is employed for the spatial discretization along with the second order Adams-Bashforth and the first order backward-Euler time integration. The calculated cylinder vibration frequency is between 0.60 and 1.30 times of the natural vortex-shedding frequency. The calculated oscillation amplitude extends to 25% of the cylinder diameter and in the case of the lock-in region it is 60%. It is made clear that the cylinder oscillation has influence on the wake pattern, the time histories of the drag and lift forces, power spectral density and phase diagrams, etc. It is found that these results include both the periodic (lock-in) and the quasi-periodic (non-lock-in) state. The vortex shedding frequency equals the driving frequency in the lock-in region but is independent in the non-lock-in region. The mean drag and the maximum lift coefficient increase with the increase of the forcing amplitude in the lock-in state. The lock-in boundaries are also established from the present direct numerical simulation.

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Development of Efficient Numerical Method in Time-domain for Broadband Noise due to Turbulence-cascade Interaction (유입난류와 평판 캐스케이드 상호작용에 따른 광대역 소음 해석을 위한 효율적인 시간영역 수치기법의 개발)

  • Kim, Sang-Ho;Cheong, Cheol-Ung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.19 no.7
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    • pp.719-725
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    • 2009
  • An efficient time-domain numerical method for the analysis of broadband noise generation and propagation due to turbulence-cascade interaction is developed. The core algorithm of the present method is based on the B-periodicity of the acoustic response function of the flat-airfoil cascade to the ingesting gust(B denotes the number of airfoils in the cascade). To confirm this periodicity, gust-cascade interaction problem are solved by using the time-domain method, which shows that the incident gust with the circumferential mode number having the same remainders when divided by the airfoil number excites the same acoustic response of the cascade. Using the proposed fast algorithm with this periodicity, we show that the total computation time for the model broadband problem using the total 525 incident gust modes can be reduced to about 1/4 of that taken in using the previous time-domain program.

Sound Absorption Performance of Noise Barrier According to Single Number Rating Methods (단일수치 평가방법에 따른 방음벽의 흡음성능 고찰)

  • Kim, Yonghee;Lee, Sungchan
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.27 no.2
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    • pp.243-250
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    • 2017
  • In this study, single number rating methods of sound absorption coefficients are discussed. After that the sound absorption performance of noise barriers which are classified by Korea Standard are analyzed according to several standards. The existing rating methods such as NRC (noise reduction coefficient), SAA (sound absorption average) or αw (weighted sound absorption coefficient) from ASTM C423, KS F 3505 and ISO 11654 are introduced. The sound absorption performance of noise barrier is evaluated to compare NRC and αw value. When the value is over 0.6 there are large variance between NRC and αw value. As results, it is needed to unify single number rating methods of sound absorption coefficients for Korean standards on sound absorbing materials.

A numerical study on the vaporization of a droplet considering internal circulating flow in the presence of an oscillating flow (진동하는 유동장하에서 내부 순환 유동을 고려한 액적의 증발에 관한 수치적 연구)

  • Ha, Man-Yeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.5
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    • pp.1700-1716
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    • 1996
  • The two-dimensional, unsteady, laminar conservation equations for mass, momentum, energy and species transport in the gas phase and mass, momentum and energy in the liquid phase are solved simultaneously in spherical coordinates in order to study heating and vaporization of a droplet entrained in the oscillating flow. The numerical solution gives the velocity and temperature distribution in both gas and liquid phase as a function of time. When the gas flow oscillates around an vaporizing droplet, the liquid flow circulates in the clockwise or counterclockwise direction and the temperature distribution in the liquid phase changes its shapes, depending on the gas fow direction. When the gas flow changes its direction of circulating liquid flow is opposite to the gas flow, forming two vortex circulating in the opposite direction. During the heating period, the difference in the maximum and minimum temperature is large, followed by the almost uniform temperature slightly below the boiling temperature. The mass and heat transfer from the droplet depend on the droplet temperature, droplet diameter and the magnitude of relative velocity, giving the droplet lifetime different from the d2-law.

Development of Efficient Numerical Method in Time-domain for Broadband Noise due to Turbulence-cascade Interaction (유입난류와 평판 캐스케이드 상호작용에 따른 광대역 소음 해석을 위한 효율적인 시간영역 수치기법의 개발)

  • Kim, Sang-Ho;Cheong, Cheol-Ung
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2009.04a
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    • pp.477-482
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    • 2009
  • An efficient time-domain numerical method for the analysis of broadband noise generation and propagation due to turbulence-cascade interaction is developed. The core algorithm of the present method is based on the B-periodicity of the acoustic response function of the flat-airfoil cascade to the ingesting gust (B denotes the number of airfoils in the cascade). To confirm this periodicity, gust-cascade interaction problem are solved by using the time-domain method, which shows that the incident gust with the circumferential mode number having the same remainders when divided by the airfoil number excites the same acoustic response of the cascade. Using the proposed fast algorithm with this periodicity, we show that the total computation time for the model broadband problem using the total 525 incident gust modes can be reduced to about 1/4 of that taken in using the previous time-domain program.

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Numerical Study on the Control of Heavy-weight Floor Impact Noise for PC Slab Coupled with Viscoelastic Material (점탄성재료가 결합된 PC 슬래브의 중량충격음 저감에 관한 수치해석 연구)

  • Hwang, Jae-Seung;Song, Jin-Kyu;Hong, Geon-Ho;Park, Hong-Gun
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.5
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    • pp.533-540
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    • 2008
  • In this study, a new slab system where a part of precast slab is connected each other by viscoelastic material is proposed and numerical analysis is performed to evaluate the effect of the connection between the material and PC slab on the vibration and noise control. Substructuring is introduced to develop the equation of motion for the slab system. In addition, the optimal properties of viscoelastic material are investigated. For the performance evaluation of the new slab system, the sound power and acceleration responses of the slab are compared with those of two way slab and one way slab, respectively. Numerical analysis results show that the sound power of the new slab system can be reduced by viscoelastic material significantly.