• Title/Summary/Keyword: boundary characteristics

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Numerical Analysis of Wintertime Air Pollution in East Asia Region Using Long-Range Transport Model

  • Jang, Eun-Suk
    • Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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    • v.4 no.2
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    • pp.103-110
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    • 2000
  • In order to understand the wintertime intermittent characteristics of the trans-boundary air pollutant transport observed in East Asia, a numerical simulation of the long-range transport of pollutants was applied using an atmospheric transport model(STEM-II). The numerical simulation was carried out for the entire month of January 1997 and specific atmospheric aerosol (including sulfate, nitrate, and other ion compounds0 observation data were compared from four observation sites(Cheju Island, Kanghwa Island, Dazaifu, and Fukue Island). The observation data revealed that concentration peaks were intermittently observed at 3 to 4-day intervals plus the four observation sites exhibited a very similar spatial variation. The horizontal and spatial scale of the heavily polluted air masses was analyzed based on numerical results. The mechanism of the intermittent transport of air pollutants was clearly explained by a comparison of the observed data with the numerical output. It was found that the wind pattern variations associated with the synoptic scale pressure system changes play an extremely important role in the transport of pollutants in this region.

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Flow and Noise Characteristics of NACA0018 by Large-Eddy Simulation (LES를 이용한 NACA0018 에어포일 주위의 유동 및 이산소음계산)

  • KIM, H.-J.;LEE, S.
    • 유체기계공업학회:학술대회논문집
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    • 2002.12a
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    • pp.433-438
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    • 2002
  • The flow field around a symmetrical airfoil in a uniform flow under the generation of noise was numerically studied and compared with experimental datum. The numerical simulation was carried out by LES which employs a deductive dynamic model as subgrid-scale model. The result of an attack angle of $6^{\circ}$ indicate that the discrete frequency noise is generated when the separated laminar flow reattaches near the trailing edge of the pressure side and the turbulent boundary layer is formed over the suction side of the airfoil near the trailing edge. The periodic behavior of vortex formation was observed around the trailing edge and it persists further downstream in the wake. The frequency of the vortex formation in the wake was consistent with that of the discrete frequency noise.

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Computational Fluid Dynamics Analysis of Wind Tunnel Test for Natural Laminar Flow Airfoil (자연층류 익형 풍동시험 전산유체해석)

  • Kim, Cheol-Wan;Lee, Yung-Gyo
    • Aerospace Engineering and Technology
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    • v.7 no.2
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    • pp.27-30
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    • 2008
  • Wall correction method for wind tunnel test is reviewed and applied to the numerical experimental results obtained at the wind tunnel condition. The corrected lift coefficient agrees well with the reference data generated from the grid having very far boundary However the corrected drag coefficient presents some deviation from the reference data.

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Design Method for the Electromagnetic Wave Absorber at 9.45 GHz (9.45GHz용 전파흡수체의 설계 방법)

  • 김왕섭;김경용
    • The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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    • v.4 no.2
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    • pp.11-16
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    • 1993
  • A design method for the electromagnetic wave absorber with the attenuation over 20 dB at a frequency was formulated. In addition to the matching boundary which is determined by the theoretical equation, several limiting conditions due to the fabrication process were examined. Based on the study on the effects of the variance of the thickness and permittivity on the electromagnetic wave absorbing characteristics, a mean to exclude such effects was also included in the proposed design method. The ranges of variables were limited as the frequency of 9.45 GHz and .epsilon.' = 5 ~ 30, when the effect of .epsilon. " was not considered.

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FLOW PAST A RECTANGULAR CYLINDER (사각 실린더를 지나는 층류 유동특성)

  • Park, Doohyun;Yang, Kyung-Soo;Ahn, Hyungsu
    • Journal of computational fluids engineering
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    • v.20 no.3
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    • pp.47-53
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    • 2015
  • This study performed numerical simulation to elucidate the characteristics of flow past a rectangular cylinder with various values of the aspect ratio(AR) of the cylinder. We calculated the flow field, force coefficients and Strouhal number of vortex shedding depending on the Reynolds number(Re) and the aspect ratio. The $AR{\approx}1$ is preferred for drag reduction, and 0.375$AR{\approx}0$ is recommended if suppression of the lift-coefficient fluctuation and the shedding frequency is desirable. Furthermore the criticality of the Hopf bifurcation is also reported for each AR.

A Study on the Prediction of Pressure ~ Time Histories by Unsteady Gas Flow through the Internal Combustion Engine Exhaust System (내연기관 배기계의 비정상 가스유동에 대한 압력-시간 파형 예측에 관한 연구)

  • M.H.Lee;J.S.Lee;B.G.Yu;K.O.Cha
    • Journal of Advanced Marine Engineering and Technology
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    • v.21 no.5
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    • pp.491-502
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    • 1997
  • This paper describes a theoretical and exprimental investigation of the pressure - time histories of some basic internal combustion engine exhaust systems. The program package is utilized the method of characteristics to solve the general equations of one - dimensional unsteady gas flow. This analysis is then combined with boundary models, based on quasi - steady flow approach, to give a complete treatment of the flow behavior in the exhaust system. Using a rotary valve exhaust simulator, experimental pressure - time histories were obtained. The predictions are com¬pared with measured results and show a high degree of correlation in amplitude and phasing.

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A Study on Dynamic Characteristics of Synchronously Controlled Hydrodynamic Journal Bearing (동기 제어되는 동압 베어링의 동특성에 관한 연구)

  • Rho, Byoung-Hoo;Kim, Kyung-Woong
    • Proceedings of the KSME Conference
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    • 2001.06c
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    • pp.311-315
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    • 2001
  • In this paper synchronous whirl of bearing is employed as control algorithm of actively controlled hydrodynamic journal bearing to suppress the whirl instability and unbalance response of a rotor-bearing system. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than conventional analysis which uses the Reynolds condition. The stability and unbalance responses of a rotor-bearing system are investigated for various control gain and phase difference between the bearing and journal motion. It is shown that the unbalance response of a rotor-bearing system can be greatly improved by synchronous whirl of the bearing, and there is an optimum phase difference, which gives the minimum unbalance response of the system, at given operating condition. It is also found that the speed at onset of instability can be greatly increased by synchronous whirl of the bearing.

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The influence of fluid inertia and heat dissipation in fluid films (유체막에서 관성과 열 소산의 영향)

  • Kim, Eun-Pil
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.2
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    • pp.224-234
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    • 1997
  • It was demonstrated earlier that for laminar, isothermal flow of the lubricant in long journal bearings, inertia has negligible effect on the load carrying capacity and influences only the stability characteristics of the bearing. The question in the present paper is: 'will these conclusions of the isothermal theory remain valid in the presence of significant dissipation, or will lubricant inertia and dissipation interact non-linearly to bring about qualitative changes in bearing performance\ulcorner' The results obtained here assert that the effect of lubricant inertia on load carrying capacity remains negligible, irrespective of the rate of dissipation. The stability of the bearing is, however, affected by lubricant inertia. These results, although obtained here for long bearings with Sommerfeld and Gumbel boundary conditions, are believed to be applicable to practical bearing operations and affirm that bearing load may be calculated from classical, i. e., non-inertial theory.

Dynamic Characteristics of an Eccentric Crack in a Functionally Graded Piezoelectric Ceramic Strip

  • Shin, Jeong-Woo;Kim, Tae-Uk;Kim, Sung-Chan
    • Journal of Mechanical Science and Technology
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    • v.18 no.9
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    • pp.1582-1589
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    • 2004
  • The dynamic response of an eccentric Griffith crack in functionally graded piezoelectric ceramic strip under anti-plane shear impact loading is ana lysed using integral transform method. Laplace transform and Fourier transform are used to reduce the problem to two pairs of dual integral equations, which are then expressed to Fredholm integral equations of the second kind. We assume that the properties of the functionally graded piezoelectric material vary continuously along the thickness. The impermeable crack boundary condition is adopted. Numerical values on the dynamic stress intensity factors are presented for the functionally graded piezoelectric material to show the dependence of the gradient of material properties and electric loadings.

Finite Element Analysis of the Contact Stress Characteristics in Scraper Seals (스크레이퍼 실의 접촉응력 특성에 관한 유한요소해석)

  • Kim, Chung-Kyun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.23 no.6 s.165
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    • pp.895-902
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    • 1999
  • This paper deals with a numerical study of the tribological contact stress distributions of elastomeric lip seals for oscillating shafts when the sealing interference and band width between the lip ease or contact seals and the shaft are present. Using the finite element method the contact stress and band width of scraper seals are analyzed for the sealing interference including some nonlinearities such as geometrical nonlinearity, material nonlinearity and nonlinear contact boundary condition. The FEM results showed that the contact stress concentrated on the contacting lip zone between the contacting edge of lip and the shaft for the increased interference. In double lip scraper seals, ole maximum contact stress of the dust lip, which is used to exclude foreign contaminants is six times higher than that of the primary sealing lip, which is used to contain lubricants.