• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 추계학술발표회논문집(1)
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• pp.481-486
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• 1997

The interfacial shear stress is experimentally investigated for co-current air-water stratified flow in inclined rectangular channels having a length of 1854mm, width of 120mm and height of 40mm at almost atmospheric pressure. Experiments are carried out in several inclinations from $0^{\circ}\;up\;to\;10^{\circ}$. The local film thickness and the wave height are measured at three locations, i.e., L/H = 8,23, and 40. According to the inclination angle, the experimental data are categorized into two groups; nearly horizontal data group ($0^{\circ}\;{\leq}\;{\theta}\;{\leq}\;0.7^{\circ}$), and inclined channel data group ($0.7^{\circ}\;{\leq}\;{\theta}\;{\leq}\;10^{\circ}$). Experimental observations for nearly horizontal data group show that the flow is not fully developed due to the water level gradient and the hydraulic jump within the channel. For the inclined channel data group, a dimensionless wave height, $\Delta$h/h, is empirically correlated in terms of $Re_{G}$ and h/H. A modified root-mean-square wave height is proposed to consider the effects of the interfacial and wave propagation velocities. It is found that an equivalent roughness has a linear relationship with the modified root-mean-square wave height and its relationship is independent of the inclination.

• 동력기계공학회지
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• 제21권2호
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• pp.48-56
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• 2017

The steady-state, incompressible and three-dimensional numerical analysis was carried out to evaluate the velocity fields around the seabed tiller used for the improvement of the seabed soil and the pulling force and buoyancy generated by driving the seabed tiller. The turbulence model used in this study is a realizable $k-{\varepsilon}$ well known to be excellent for predicting the performance of the flow separation and recirculation flow as well as the boundary layer with rotation and strong back pressure gradient. As a results, a typical vortex pair appears near the adjacent rotor vane tip. When the current is stopped, there is no force when pulling the seabed tiller, but when the current flows at 1.2 knots, the force acts on the downstream side and the pulling force is much greater. In stationary currents, the buoyancy of the seabed tiller acts more strongly towards the seabed as the number of rotations of the rotor increases, but acts more strongly toward the sea surface at 1.2 knots of current.

• 한국해안·해양공학회논문집
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• 제24권6호
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• pp.390-399
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• 2012

본 연구에서는 지속적인 담수유입이 존재하고 S자의 수로형태를 가진 경기만 석모수로에서 소조기 홍수시 13시간 동안 7개의 정선에서 단면유속 및 염분을 관측하였다. 각 단면의 최강 창조와 낙조시의 유속 크기와 방향을 파악하였고, 단면 내의 유속 분포 및 염분구조를 분석하였다. 또한 정선 별로 나타나는 횡 방향 흐름이 어떠한 운동량에 의해 지배되는지 파악하고자 횡 방향의 운동량 분석을 수행하였다. 운동량 분석에서는 석모수로의 S자 형태의 영향을 고려하기 위해서 원심력을 고려하였다. 분석 결과 소조기 홍수시 석모수로는 횡 방향 압력 경도력과 수직적 마찰력이 가장 우세하기 때문에 염분 분포와 성층에 의한 흐름이 주로 나타났다. 수로의 특성은 크게 북단과 남단으로 나누어 볼 수 있는데 상대적으로 조간대가 넓게 형성되고 담수의 영향이 큰 석모수로 북단의 4개 정선중에서 수심이 깊은 정선에서는 횡 방향 압력 경도력이 우세하지만 수직적으로 크기가 다르며, 수심이 낮은 정선에서는 수직 마찰항이 우세하였다. 이와는 달리 수심이 깊고 수로의 굴곡이 심한 석모수로 남단에서는 낙조시 지형학적 원인과 담수의 영향에 따라 이류 가속항과 원심력이 강해지게 된다. 이와 같은 결과를 종합할 때, 석모수로는 위치와 수심, 수로의 굴곡 등에 따라 운동량 분포가 각기 달리 나타나며 이러한 영향으로 인해 횡 방향 흐름 특성이 발생했음을 알 수 있다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 1998년도 창립기념 춘계학술대회 논문집
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• pp.596-603
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• 1998

The entry compression wave, which is generated at the entrance of the tunnel, is almost always associated with the pressure transients in the tunnel as well as the impulse noise at the exit of the tunnel. It is highly required to design the train nose shape that can minimize such undesirable phenomena. The objective of the current work is to investigate the effects of the train nose shape on the entry compression wave. Numerical computations were applied to one-dimensional unsteady compressible flow in high-speed railway train/tunnel systems. A various shape of train noses were tested for a wide range of train speeds. The results showed that the strength of the entry compression wave is not influenced by the train nose shape, but the time variation of pressure in the entry compression wavefront is strongly related to the train nose shape. The current method of the characteristics was able to represent a desirable nose shape for various train speeds. Optimum nose shape was found to considerably reduce the maximum pressure gradient of the entry compression wave.

• 한국항만학회지
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• 제9권2호
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• pp.25-38
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• 1995

The wind generated circulation model describes the phenomenon based on the following physical assumptions: a) As the horizontal dimension of the flow domain is several orders of magnitude larger than vertical dimension, nearly horizontal flow is realistic. b) The time taken for circulation to develop may effect on the flow domain of the earth's rotation, the contribution of the Coriolis force. c) A flow domain of large dimension results in quite large Reynolds number and the Reynolds stresses are approximated by the turbulent mean velocity gradient. d) The circulation is forced by the shear stresses on the water surface exercised by the wind. Modification made to the depth average approximation of the convective terms and the bed shear stress terms by adopting a certain distribution of current over the depth and laboratory measurements for the bed shear expression. Modification circulation patterns, energy evolution and surface profile gave the significant differences comparing with the classical model results. The modified model results in higher free surface gradients balancing both the free surface shear and the bed shear and consequently to higher surface profiles along the coast.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.825-830
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• 2004

A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc (DCA) compressor cascades. Two types of double-circular-arc cascades were used in this analysis. The appropriate turbulence model for compressor analysis was selected among the conventional turbulence models such as Baldwin-Lomax, k-$\varepsilon$ and k-$\varepsilon$ models. The results of current study were compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE/PWIM algorithm for collocated grid and hybrid scheme for the convective terms were the main features of numerical tools. As commonly known, turbulence modeling is very important for the prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. For selection of turbulence model, 2-D analysis was performed. And then, k-$\varepsilon$ turbulence model with wall function chosen as the reasonable turbulence model for 3-D calculation was used to increase the efficiency of computation times. A reasonable result of 3-D flow pattern passing through the double-circular-arc cascade was obtained.

• 한국도로학회논문집
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• 제17권5호
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• pp.123-133
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• 2015

PURPOSES : This study aimed to develop a new highway capacity estimation method and provide comparative results among traditional capacity estimation methods and the recommended values in the latest version of KHCM. METHODS : The limitations of the existing methods, such as inconsistency and underestimation of the capacity value, are summarized through an extensive literature review. To overcome these limitations, a new method is introduced by adopting a definition of capacity and traffic flow characteristics at or near breakdown points. This method can produce the capacity value by searching a point corresponding to the maximum traffic flow through analysis of gradient changes (point of inflection) of the traffic flow and speed distribution. Comparative results of capacity values from each method are also presented to validate the new method by using data collected from detectors on freeways. RESULTS: From the analysis results, it is shown that a consistent capacity value can be estimated by applying the new method. In addition, the resulting capacity values are 3%-4% higher than those recommended in KHCM. CONCLUSIONS : The capacity values listed in the current KHCM tend to produce underestimated results. The new method presented in this paper may be included in the future edition of KHCM.

• 전기학회논문지
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• 제58권8호
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• pp.1463-1471
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• 2009

In this paper, a new algorithm of Integrated Volt/Var Control (IVVC) is proposed using Volt/Var control for the Distribution Automation System (DAS) based on the modeling of the distributed load and the distributed current. In the proposed, the load flow based on the modeling of the distributed load and the distributed current are estimated from constants of four terminals using the measurement of the current and power factor from a Feeder Remote Terminal Unit (FRTU). For Integrated Volt/Var Control (IVVC), the gradient method is applied to find optimal solution for tap and capacity control of OLTC (On-Load Tap Changers), SVR (Step Voltage Regulator), and SC (Shunt Condenser). What is more Volt/Var control method is proposed using moving the tie switch as well as IVVC algorithm using power utility control. In the case studies, the estimation and simulation network have been testified in Matlab Simulink.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.95_96
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• 2009

In this paper, a new algorithm of Integrated Volt/Var Control (IVVC) is proposed using Volt/Var control for the Distribution Automation System (DAS) based on the modeling of the distributed load and the distributed current. In the proposed, the load flow based on the modeling of the distributed load with Distributed Generation and the distributed current are estimated from constants of four terminals using the measurement of the current and power factor from a Feeder Remote Terminal Unit (FRTU). For Integrated Volt/Var Control (IVVC), the gradient method is applied to find optimal solution for tap and capacity control of OLTC (On-Load Tap Changers), SVR (Step Voltage Regulator), and SC (Shunt Condenser). What is more Volt/Var control method is proposed using moving the tie switch as well as IVVC algorithm using power utility control. In the case studies, the estimation and simulation network have been testified in Matlab Simulink.

• 한국해양학회지
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• 제21권4호
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• pp.203-210
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• 1986

선형, 평행 수송모델을 세우고 이상적인 항해에 적용하였다. 이 간단한 해석 모델로서 지금 까지 예지되어 온 황해 남부의 역풍류 현상을 적절히 설명할 수 있 다. 수심이 임계수심(본모델 바다에서는 Hc=53m임)보다 깊은 해역에서는 압력 경도 력이 바람응력보다 우세하여 역풍류를 야기시킨다. 추정된 역풍류 속도는 풍속과 함께 증가하며 최대 역풍류는 황해의 깊은 골을 따라나타난다. 하계의 전형적인 남 풍속도 5-10노트에 대해서 황해골을 따른 역풍류(남향류)속도는 1-5cm s$^{-1}$로 추정된다. 반면에 동계의 전형적인 북풍속도 10-15노트에 대해서는 역풍류(북향류) 속도는 5-12cm s$^{-1}$ 이다. 이와 같은 속도 범위는 각각 하계의 황해 저층냉수 와 동계의 황해난류의 잠입속도에 대한 개략적인 추정치로서 사용될 수 있다.