• International Journal of Aeronautical and Space Sciences
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• 제14권3호
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• pp.201-209
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• 2013

Much numerical and experimental research has been done for the flow around an oscillating airfoil. The main research topics are vortex shedding, dynamic stall phenomenon, MAV's lift and thrust generation. Until now, researches mainly have been concentrated on analyzing the wake flow for the variation of frequency and amplitude at a low angle of attack. In this study, wake structures and acoustic wave propagation characteristics were studied for a plunging airfoil at high angle of attack. The governing equations are the Navier-Stokes equation with LES turbulence model. OHOC (Optimized High-Order Compact) scheme and 4th order Runge-Kutta method were used. The Mach number is 0.3, the Reynolds number is, and the angle of attack is from $20^{\circ}$ to $50^{\circ}$. The plunging frequency and the amplitude are from 0.05 to 0.15, and from 0.1 to 0.2, respectively. Due to the high resolution numerical method, wake vortex shedding and pressure wave propagation process, as well as the propagation characteristics of acoustic waves can be simulated. The results of frequency analysis show that the flow has the mixed characteristics of the forced plunging frequency and the vortex shedding frequency at high angle of attack.

• 국제초고층학회논문집
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• 제5권2호
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• pp.95-103
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• 2016

One of the key problems in the design of high-rise commercial complex is how to guide reasonable pedestrian distribution in commercial space. In this study, pedestrian distribution in three high-rise commercial complexes in Shanghai and Hong Kong was studied using spatial configuration analysis software Space Syntax and quantification of physical elements in commercial spaces, such as functional attractiveness, entrances, escalators, level variations and passage width. Additionally, in an attempt to integrate functions with spatial integration and spatial depth, two combination variables, the spatial coefficient of function (IF) and spatial depth coefficient of function (F/D), were proposed. The results of the correlation analysis and multiple regression analyses reflected the following: (1) Regarding the influence on pedestrian distribution, there was a synergistic and complementary relationship between function and space; (2) The comprehensive flow distribution analytic model could successfully interpret flow distribution in high-rise commercial complexes and its R Square ranged up to about 70% in the three cases; (3) The spatial coefficient of function (IF) and spatial depth coefficient (F/D) could effectively integrate functions and spatial configuration, which could help close the gap between over-emphasis on function in commercial research and the lack of consideration of function in space-syntax analysis.

• 한국항공우주학회지
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• 제37권11호
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• pp.1140-1147
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• 2009

펌프공급방식 액체로켓엔진 가스발생기의 매니폴드를 대상으로, 연료 및 산화제의 유량 균일성을 파악하기 위하여 유동해석을 수행하였다. 3가지의 연료링과 3가지의 분사기 헤드 형상에 대하여 유동해석을 수행함으로써, 유량균일성을 검토하였다. 이를 통해 최적의 유량균일성을 가지는 연료링과 분사기 헤드의 형상을 결정하였다. 또한 분사기 출구에서의 혼합비 분포를 유동해석 결과로부터 도출하였다. 이를 통하여, 연료와 산화제 모두 유량균일성이 우수한 형상을 결정할 수 있었다.

• 대한수학회논문집
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• 제34권1호
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• pp.287-301
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• 2019

In this paper we study monotonicity the first eigenvalue for a class of (p, q)-Laplace operator acting on the space of functions on a closed Riemannian manifold. We find the first variation formula for the first eigenvalue of a class of (p, q)-Laplacians on a closed Riemannian manifold evolving by the Ricci-Bourguignon flow and show that the first eigenvalue on a closed Riemannian manifold along the Ricci-Bourguignon flow is increasing provided some conditions. At the end of paper, we find some applications in 2-dimensional and 3-dimensional manifolds.

• 한국항공우주학회지
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• 제35권2호
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• pp.136-142
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• 2007

본 연구에서는 초음속 충동형 터빈의 유동특성을 알아보기 위해 소형 초음속 풍동을 설계하였다. 실험은 2차원 초음속 노즐과 익렬을 조합하여 터빈 설계 인자 중의 하나인 터빈 축 간격비에 따라 실시하였으며 단일경로 슐리렌(Schlieren) 시스템을 이용하여 유동을 가시화하였다. 그리고 다채널 압력측정 시스템을 이용하여 터빈 익렬 내의 정압력과 전압력을 측정하였다. 이러한 실험을 통해 충격파를 포함한 복잡한 유동 형태와 유동박리, 충격파-경계층 상호작용 등을 관찰할 수 있었다.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4776-4797
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• 2022

In the one-dimensional thermal-hydraulic (TH) codes, a subcooled boiling model to predict the void fraction profiles in a vertical channel consists of wall heat flux partitioning, the vapor condensation rate, the bubbly-to-slug flow transition criterion, and drift-flux models. Model performance has been investigated in detail, and necessary refinements have been incorporated into the Safety and Performance Analysis Code (SPACE) developed by the Korean nuclear industry for the safety analysis of pressurized water reactors (PWRs). The necessary refinements to models related to pumping factor, net vapor generation (NVG), vapor condensation, and drift-flux velocity were investigated in this study. In particular, a new NVG empirical correlation was also developed using artificial neural network (ANN) techniques. Simulations of a series of subcooled flow boiling experiments at pressures ranging from 1 to 149.9 bar were performed with the refined SPACE code, and reasonable agreement with the experimental data for the void fraction in the vertical channel was obtained. From the root-mean-square (RMS) error analysis for the predicted void fraction in the subcooled boiling region, the results with the refined SPACE code produce the best predictions for the entire pressure range compared to those using the original SPACE and RELAP5 codes.

• Kyungpook Mathematical Journal
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• 제59권2호
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• pp.341-352
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• 2019

Let M be an n-dimensional closed Riemannian manifold with metric g, $d{\mu}=e^{-{\phi}(x)}d{\nu}$ be the weighted measure and ${\Delta}_{p,{\phi}}$ be the weighted p-Laplacian. In this article we will study the evolution and monotonicity for the first nonzero eigenvalue problem of the weighted p-Laplace operator acting on the space of functions along the Yamabe flow on closed Riemannian manifolds. We find the first variation formula of it along the Yamabe flow. We obtain various monotonic quantities and give an example.

• 천문학회보
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• 제46권2호
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• pp.47.2-47.2
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• 2021

The present study is focused on origins of the flow and magnetic structure involved in the formation and eruption of a solar prominence. To clarify them, we performed an MHD simulation based on the 3-dimensional emerging flux tube (3DEFT) model, in which self-consistent evolution of a flow and magnetic field passing freely through the solar surface was obtained by seamlessly connecting subsurface dynamics with surface dynamics. By analyzing Lagrangian displacements of magnetized plasma elements, we demonstrate the flow structure which is naturally incorporated to the magnetic structure of the prominence formed via dynamic interaction between the flow and magnetic field.

• 한국항공우주학회지
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• 제45권6호
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• pp.447-454
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• 2017

난류 유동장으로 분사되는 두가지 형태의 액체 제트 (수평분사는 디젤연료와 수직분사는 물)의 액주 분열과 미립화 현상에 관한 이상(Two-phase) 유동에 대해 3차원 LES 수치해석을 수행하였다. 기체상태의 공기 유동은 오일러리안 해법을 사용하고, 액체 제트의 액적 추적은 라그랑지안 해법을 사용하여 기체-액체간 이상유동 해석을 수행하였다. 두 종류의 확률론적 분열 모델(Stochastic breakup model)을 사용하여 액적 분열을 모사하였으며, 액체제트의 침투깊이와 액적 분포(Sauter Mean Diameter)를 실험결과와 비교하여 미세하게 분열되는 액체 제트의 분열 현상에 대해 확률론적 분열 모델링의 적합성을 제시하였다.

• 한국안전학회지
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• 제30권6호
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• pp.63-69
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• 2015

In this study, a 2D hydrodynamic model equipped with critical dry depth scheme was developed to reproduce the flow over staircase. The channel geometry of hydraulic experiment conducted by Ishigaki et al. was generated in the computational space, and the developed model was validated against flow properties such as discharge, velocity and momentum. In addition, the water surface profile and the velocity distribution evolved in flow over two layers staircases were analyzed. When the initial water depth at the upper floor was 0.3 m, the maximum velocity at lower floor was 4.2 m/s, and the maximum momentum was $1.2m^3/s^2$, and its conversion to force per unit width was 1.2 kN/m. This value was equivalent to the hydrostatic force with 50 cm water depth, and evacuation became difficult, as proposed by Ishigaki et al. For the flow over staircases connecting two layers, the maximum run-up height in flat part connecting two layers was approximately two times higher than the initial water depth in upper floor, and the rapid shock wave with sharp front and long tail was propagated.