• Title/Summary/Keyword: 스톡스 수

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Dependence of the time resolved anti-Stokes Raman signal on the correlation between pump and Stokes waves (시분해 반스톡스 라만 분광 신호의 스톡스광과 펌프광의 상관관계에 대한 의존성 계산)

  • 고춘수
    • Korean Journal of Optics and Photonics
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    • v.8 no.5
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    • pp.372-376
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    • 1997
  • We study the time resolved anti-Stokes Raman spectroscopy with correlated pump and Stokes waves. When only two pump waves with relative delay are incident into a Raman medium, the Stokes waves generated by stimulated Raman scattering couple with the pump waves to generate anti-Stokes signal. Since the correlation between Stokes and the pump waves are not perfect and not quantified yet, we make a simple model fot it and calculate the normalized anti-Stokes signal intensities as a function of time delay. The broadband light regarded as chaotic field.

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Effects of Characteristic Condition Number on Convergence in Calculating Low Mach Number Flows, II : Navier-Stokes Equations (저속 유동 계산의 수렴성에 미치는 특성 조건수의 영향 II : 나비어스톡스 방정식)

  • Lee, Sang-Hyeon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.36 no.2
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    • pp.123-130
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    • 2008
  • The effects of characteristic condition number on the convergence of preconditioned Navier-Stokes equations were investigated. The two-dimensional preconditioned Navier-Stokes adopting Choi and Merkle's preconditioning and the temperature preconditioning are considered. Preconditioned Roe's FDS scheme was adopted for spatial discretization and preconditioned LU-SGS scheme was used for time integration. It is shown that the convergence characteristics of the Navier-Stokes equations are strongly affected by the characteristic condition number. Also it is shown that the optimal characteristic condition numbers for viscous flows are larger than that in inviscid flows.

연소진단 용 광대역 코헤런트 반 스톡스 라만 분광기의 제작 및 정확도 분석.

  • Park, Cheol-Ung;Park, Seung-Nam;Han, Jae-Won;Park, Bu-Min;Sin, Hyeon-Dong
    • 한국연소학회:학술대회논문집
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    • 1997.06a
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    • pp.33-44
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    • 1997
  • 연소상태의 온도를 이동하면서 측정할 수 있는 광대역 코헤런트 반스톡스 라만 분광기를 제작하였다. 분광기의 온도 측정 정확도를 향상시키기 위하여 무모드레이저를 제작하여 스톡스광으로 사용하였다. 이동형 CARS 분광기에 적합하도록 CARS신호 측정용 단색기를 제작하여 분광기 내부에 설치 하였다. CARS 분광기의 온도 측정의 정확도를 알아보려고 흑연관 전기로를 이용하여 표준 복사온도계와 CARS 분광기로 측정한 온도의 차이를 측정하였다. 장치의 온도 정확도는 1000 K - 2400 K 사이의 온도영역에서 2%이내 였다. 무모드 색소레이저의 출력 스펙트럼의 시간에 따른 안정도를 측정하여 온도측정에 미치는 오차를 조사한 결과 1500 K에서 5 시간 동안 1.5 %이내 였다. 평면 화염 버너에서 프로판공기 예혼합 화염의 온도 분포를 측정하여 이 장치의 응용 가능성을 확인하였다.

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Study of Stokes Flow Past a Vertical Plate in a Two-Dimensional Channel (2차원 채널 내의 수직 평판을 지나는 스톡스 유동에 대한 연구)

  • Yoon, Seok-Hyun;Jeong, Jae-Tack
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.6
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    • pp.609-615
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    • 2011
  • A two-dimensional Stokes flow past a vertical plate in a channel is analyzed. The vertical plate is located at the center of the channel, and plane Poiseuille flow exists far upstream and downstream of the vertical plate. The Stokes approximation is used, and the flow is investigated analytically using the method of eigenfunction expansion and the point collocation method. From the analysis, the stream function and pressure distribution are obtained, and the pressure and shear stress distributions on the plate and channel wall are calculated. The additional pressure drop induced by the vertical plate and the force exerted on it are calculated as functions of the length of the vertical plate. For a typical length of the vertical plate, the streamline pattern and pressure distribution are shown. In addition, numerical analysis of laminar flow with a small Reynolds number is carried out to analyze the effect of a small Reynolds number on the flow pattern.

Temperature Preconditioning for Improving Convergence Characteristics in Calculating Low Mach Number Flows, II: Navier-Stokes Equations (저속 유동 계산의 수렴성 개선을 위한 온도예조건화 II: 나비어스톡스 방정식)

  • Lee, Sang-Hyeon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.12
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    • pp.1075-1081
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    • 2007
  • The temperature preconditioning is applied to the Navier-Stokes equations. Also, a new concept of diffusion Mach numbers is introduced to modify the reference Mach number for the Navier-Stokes equations. Flows over a circular cylinder were calculated at different Reynolds numbers. It is shown that the temperature preconditioning improves the convergence characteristics of Navier-Stokes equations. Also, it is shown that the modified reference Mach number alleviates the convergence problems at locally low speed regions.

Numerical Analysis of Viscous Flow on the Periodic Oscillating Flat Plate using Unsteady CFD Code (비정상 CFD 코드를 이용한 주기성 하모닉 진동 평판 위의 점성유동 수치해석)

  • Lee, Eunseok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.1000-1002
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    • 2017
  • Here, the unsteady Navier-Stokes solver has been developed using implicit dual time stepping method. The implicit dual time stepping method introduced the pseudo time step for solving the new residual including the steady state residual and real time derivative. For the validation of code, Stokes 2nd problem, the laminar flow on the oscillating flat plate was selected and compare the calculating results with analytic solutions. The calculating velocity profile and skin friction has a good agreement with analytic solutions.

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Analysis of Laminar Flows around Submerged Spheres (물 밑에 잠긴 구 주위의 층류 유동장 해석)

  • Kwag, Seung-Hyun
    • Journal of Advanced Marine Engineering and Technology
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    • v.34 no.8
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    • pp.1094-1099
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    • 2010
  • Three dimensional laminar flows are numerically simulated around the submerged spheres. The finite volume based Navier-Stokes equations with unstructured grids are solved to make clear the hydrodynamic phenomena near and far away from the body. Reviews are made on with the vorticity, velocity, dynamic pressure, residuals, drags, etc. The Reynolds numbers under consideration are 425, 300, 250 and 100. In case of small spacing between spheres, the flow is more stable than that past a single sphere. According to the analysis, the flow past two spheres is found to be unstable as the spacing becomes larger. The rear sphere shows the deduction of stagnation pressure, which results in the decrease of the resistance. The predicted drag coefficients verify that the present numerical calculation is reasonable.

A Study on Ocean Waves with Free Surface around the Moving Underwater Vehicle (항해중인 잠수정 주위의 자유표면 해양파 연구)

  • Seung-Hyun Kwag
    • Journal of the Korean Institute of Navigation
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    • v.25 no.4
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    • pp.471-476
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    • 2001
  • 항해중인 잠수정 주위의 해양파를 재연하기 위하여 3차원 비압축성 나비에-스톡스 코드가 사용되었다. 수치적으로는 3차미분 풍상차분이 근간을 이룬다. 대양에서 항해 중인 선박에 적용을 하기 위해 프루드 수를 0.4에서 0.7까지로 하였다. 조파저항, 양력, 모우멘트, 압력분포가 재연되었고 이것은 조선소의 초기설계에 사용 할 수 있다. Marker & Cell 방법을 기본으로 사각격자 구조를 만들어 해석하였고, 검증을 위하여 기존의 실험 결과와 비교하였다.

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Optimum Inverse Design of 2-D Cascade Airfoil (2차원 익렬 익형의 최적역설계)

  • 조장근;박원규
    • Journal of the Society of Naval Architects of Korea
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    • v.39 no.4
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    • pp.17-23
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    • 2002
  • The present paper describes the optimum inverse design of 2-D linear cascade airfoil. The pressure coefficient of an airfoil surface is taken as the objective function, and non-orthogonal incompressible Navier-Stokes equation is applied to calculate the pressure coefficient. Both of steepest descent and conjugate gradient method have been used to make the objective function go to zero. The 1st order finite differential method is applied to the searching direction and the golden section method is used to compute the searching distance. As a result of the present work, a good convergence to the target airfoil has been obtained.

Simulation of Viscous Flow around a Circular Cylinder between Parallel Walls

  • Kwag, Seung-Hyun
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2002.10a
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    • pp.212-216
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    • 2002
  • 평행한 벽 내부의 흐르는 규제 속에 원형실린더를 놓고 운동장 해석을 수행하였다. 비압축성 Navier- Stokes 방정식을 풀었고 3차 풍상미분의 수치해법을 이용하였다. 채널 내부에서 실린더의 위치를 이동하면서 벽면의 효과 전단력, 와류의 현장을 규명하였다. 수치처리는 Marker & Cell 기법에 의한 유한차분법을 사용하였다. 본 연구를 통하여 실린더와 벽 경계 사이에서의 생성된 와가 박리 전단에 영향을 미치는 것을 알 수 있었다.

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