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Micro Surface-roughness Effect on the Flow Induced by Rotating Disk
박준상(J. S. Park),윤명섭(M.S. Yoon),현재민(J.M. Hyun) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
An analytic study has been made of the slip velocity over rotating disk with micro surface roughness. The system Ekman number, E≡V/ΩR², is assumed to be very small value, in which denotes kinematic viscosity of the fluid, Ω rotational angular velocity of the disk and radius of the disk. Amplitude of the surface roughness, δ, which is a characteristic length scale of roughness, is equal to or less than the thickness of Ekman boundary layer, i.e., δ≤O(E<SUP>1/2</SUP>). Implementing a strained coordinate method to the Ekman layer flow, the flow field solutions are obtained as a form of explicit formula, and then effective slip velocity conditions are clearly defined on the geometrical mean plane. The results are confirmed by comparing with numerical data. Several in-depth physics underlying the solution are discussed.
Flow in a cylinder driven by a rotating endwall disk with concentrically-grooved sinusoidal surface
박준상(J.S. Park),윤명섭(M.S. Yoon),현재민(J.M. Hyun) 한국유체기계학회 2007 유체기계 연구개발 발표회 논문집 Vol.- No.-
The flow in a rotating cylinder driven by the differential rotation if its bottom endwall disk with a sinusoidal surface roughness, i.e., <SUP>z</SUP>b = aㆍcos(2πNr) has been studied by linear theoretical analysis and numerical computation to the steady axisymmetric Navier-Stokes equations, where <SUP>z</SUP>b denotes the height of bottom disk surface, a the wave amplitude and N the wave number of the bottom surface. From the linear analysis, analytic series solutions of the velocity field in a boundary layer near the wavy disk are secured under an assumption of mild slope, i.e., |<SUP>z</SUP>b| < O (1). The linear solution also shows that torque characteristics are highly correlated to roughness parameter of (aN), not to wave amplitude a and wave frequency N alone of the rotating disk. Full nonlinear numerical analysis to the Navier-Stokes equations has performed and a comprehensive description is given on roughness effect of the disk to the flow fields. Qualitatively, flow dynamic ingredients of the nonlinear flow are still consistent with linear problem, i.e., all flow characteristics such as torque, primary and secondary volume flow rates and peak value of the azimuthal velocity being correlated to roughness parameter (aN). However, parametric dependence shows some deviation: flow variables depend on O((aN)²) for the linear case and O((aN)¹) for the full nonlinear case.
지영무(Y.M. Ji),신영섭(Y.S. Shin),박준상(J.S. Park),현재민(J.M. Hyun) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Two dimensional sloshing problem in a rigid rectangular tank with free surface is considered. The flow is generated by the motion of container being in harmonic motion in time along the horizontal axis, i.e., the container being excited by u = Asin(2πft) where u denotes the container velocity externally imposed, A the amplitude of oscillation velocity and f the frequency of oscillation. Thus, the displacement S of the container for a cycle is defined as S = A/f. An experimental apparatus is arranged to investigate large amplitude sloshing flows in off-resonant condition, where large amplitude means that A~O(1) and the distance, S is comparable with the breadth, L of container, i.e., L/S~O(1). Comprehensive PIV-data have been obtained, and those show that flow physics on nonlinear off-resonant sloshing problem can be characterized into three peculiar free surface motions: standing wave motions being similar with those of linear sloshing, run-up phenomenon along the vertical sidewall at the moment of turn-over of the container and gradually propagating bore motion from the sidewall to interior fluid region like hydraulic jump.
철도 노반용 합성고무계 개질아스팔트의 유변학적 물성 평가
김혁중(Hyeok J. Kim),이진욱(Jin W. Lee),박준상(Jun S. Park),박대욱(Dae W. Park),나일호(Il-Ho Na) 한국철도학회 2014 한국철도학회 학술발표대회논문집 Vol.2014 No.10
본 연구에서는 철도노반용 재료로써 SBS개질제를 첨가하여 PG76-22등급을 만족하면서 고온 소성변형 및 수분민감성 개선을 목표로 실험을 수행하였다. 당 연구에서 특화된 개질 아스팔트를 사용하는 목적으로는 첫째, 기존 자갈/슬래브궤도 대비 유지보수의 편의성과 경제성 제고. 둘째, 차별화 성능(저진동/소음,장기 공용성 확보) 구현이다. 이에, 금번 연구에서는 연차별 수행된 선행 연구의 실험 결과를 기반으로 합성 고무계(SBS) 제품과 기능성 첨가제를 컴파운딩하여 최적 배합을 도출하였다. 또한, 아스콘 플랜트의 생산성 제고 및 품질 안정성 기준 만족하기 위해 개발된 개질제의‘상분리 제어, 배합조건 최적화(용융속도 및 시간)’등 유변학적 물성 및 혼합물 평가를 통해 철도노반용 재료로써의 최적 물성을 도출하고자 한다. In this study, the experiment was performed to optimize the properties of high temperature rutting resistance and the moisture susceptibility using SBS modifier to satisfy with PG 76-22 grade for the railway roadbed. We used a modified asphalt specialized in railway. The purpose of using a specific modified asphalt is providing economic efficiency and maintenance compared to the original track, and differentiated performance (vibration / noise, long-term performance). Thus, this study were derived modified asphalt based on the optimal formulation by mixing synthetic rubber (SBS) and the functional additive through the study of several years. In addition, we performed an evaluation of the rheological properties of asphalt modifiers(the control of phase separation, melting time of modifier) to meet asphalt plant productivity and the standard of quality stability.
김영신(Y. S. Kim),지영무(Y. M. Ji),이재우(J.-W. Lee),박준상(J. S. Park) 한국전산유체공학회 2004 한국전산유체공학회 학술대회논문집 Vol.2004 No.-
This paper describes a supersonic separation of air-launching rocket from the mother plane. Three dimensional Euler equations were numerically solved to analyze steady/unsteady state fluid flows. To solve the Euler equations, named CFD- FASTRAN that is commercial computation code. The results of simulation clearly demonstrate effect of shock-expansion wave interaction between the rocket and the mother plane. Moreover, important influential factors at separating stage of the rocket were extracted with a comprehensive analysis. Finally, from the consideration of supersonic-separation, a guideline to safety-separation is given to the design of supersonic air-launching rocket.