• 한국항공운항학회지
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• 제5권1호
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• pp.51-63
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• 1997

Generally, air freight forecasting model used to major factor GNP(GDP), Yield, Exchange rate, as its independent variables. We studied about the factors that affect to Air Freight in Korea, and we found six affective variables. Those are GNP, Exchange rate, Flight routes, Flight numbers, Sum of dollars Export and import. To find the relationship between the Air Freight and GNP, Exchange rate, Flight routes, Flight numbers, Sum of dollars Export and import we used regression analysis. Through the regression analysis, we found some problems in the model. There are collieneraities between the variables, so we took the variables selection model to choose the best affective variables of air cargo. We have defined the the Korean air freight forecasting model with two variables and forecast far the $1996{\sim}2010$ period were made by using this model.

• 한국군사과학기술학회지
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• 제10권1호
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• pp.130-143
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• 2007

Using steady state aerodynamic theories, it has been claimed that insects and birds cannot fly. To make matters worse, insects and birds fly at low Reynolds numbers. Therefore, a recurring theme in the literature is the importance of understanding unsteady aerodynamic effect and how the vortices behave when they separate from the moving surface that created them. In flapping flight, birds and insects can modify wing beat amplitude, stroke angle, wing planform area, angle of attack, and to a lesser extent flapping frequency to optimize the generation of lift force. Some birds are thought to employ two different gaits(a vortex ring gait and a continuous vortex gait) and unsteady aerodynamic effect(Clap and fling, Delayed stall, Wake capture and Rotational Circulation) in flapping flight. Leading edge vortices may produce an increase in lift. The trailing edge vortex could be an important component in gliding flight. Tip vortices in hovering support the body weight of the hummingbirds. Thus, this study investigated how insects and birds generate lift at low Reynolds numbers. This research is written to further that as yet incomplete understanding.

• 한국항공우주학회지
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• 제37권9호
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• pp.931-938
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• 2009

비행시험은 개발 항공기의 다양한 성능검증을 포함하여 감항기술기준에 대한 안전성을 입증하는 최종시험으로서 중요성이 크다. 특히, 민간 항공기의 비행시험은 개발업체의 경험 및 노하우에 의해 기술 보호성격이 강하며, 다양한 시험항목과 비행조건에 의해 비용이나 시간측면에서 효율적인 비행시험 수행 및 비행시험 기법의 확보는 필수적이다. 본 논문에서는 이륙 및 착륙성능 입증을 위한 이착륙 비행시험에 대해 지상관측법과 DGPS를 활용한 비행시험 기법을 제안하고 실제 비행시험을 수행하여 그 결과를 비교하였다.

• Steel and Composite Structures
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• 제24권1호
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• pp.93-112
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• 2017

Metaheuristic algorithms in general make use of uniform random numbers in their search for optimum designs. Levy Flight (LF) is a random walk consisting of a series of consecutive random steps. The use of LF instead of uniform random numbers improves the performance of metaheuristic algorithms. In this study, three discrete optimum design algorithms are developed for steel skeletal structures each of which is based on one of the recent metaheuristic algorithms. These are biogeography-based optimization (BBO), brain storm optimization (BSO), and artificial bee colony optimization (ABC) algorithms. The optimum design problem of steel skeletal structures is formulated considering LRFD-AISC code provisions and W-sections for frames members and pipe sections for truss members are selected from available section lists. The minimum weight of steel structures is taken as the objective function. The number of steel skeletal structures is designed by using the algorithms developed and effect of LF is investigated. It is noticed that use of LF results in up to 14% lighter optimum structures.

• 한국가시화정보학회지
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• 제19권3호
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• pp.46-53
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• 2021

In the present study, wind tunnel experiments were performed to reduce the drag of a paragliding helmet in the range of Reynolds numbers from 46,000 to 155,000. The drag force of the helmet model with dimples and deflectors installed was measured by varying the dimple depth and the slant angle of the deflector. The dimples were effective in reducing the drag at low Reynolds numbers, but no significant drag reduction was found in the Reynolds number range in which an actual paraglider flight takes place. On the other hand, the deflector installed tangentially to the side outline of the helmet showed an average drag reduction of 7% in the flight Reynolds number range of real paragliding. This was because the deflector shrunk the size of the wake region and moved the wake region downstream of the deflector.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.248-256
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• 2001

Capacities of screw are pumping, steady flow of polymer melts, volumetric efficiency, steady volumetric throughout etc. they are affected by geometry of screw, heat flux, pressure on inside barrel, rotating velocity, friction coefficient at screw surface etc. Also the temperature of polymer melts by heating pad and injection pressure play a very important role in the injection molding machine. by computation volumetric efficiency increases as rotating velocity increases, flight number increses, and decreases as friction coefficient increases. but volumetric throughout is different :s flight number increases with helix angle variability. so in this paper we analyze thermal distortion and stress of screw includes pressure and temperature distributions by finite element analysis to understand what design factors influence on thermo-mechanical characteristics of screw.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.671-679
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• 2008

The effect of Pre-cooled Turbojet Engine installation and nozzle exhaust jet on Hypersonic Turbojet EXperimental aircraft(HYTEX aircraft) were investigated by three-dimensional numerical analyses to obtain aerodynamic characteristics of the aircraft during its in-flight condition. First, simulations of wind tunnel experiment using small scale model of the aircraft with and without the rectangular duct reproducing engine was performed at M=5.1 condition in order to validate the calculation code. Here, good agreements with experimental data were obtained regarding centerline wall pressures on the aircraft and aerodynamic coefficients of forces and moments acting on the aircraft. Next, full scale integrated analysis of the aircraft and the engine were conducted for flight Mach numbers of M=5.0, 4.0, 3.5, 3.0, and 2.0. Increasing the angle of attack $\alpha$ of the aircraft in M=5.0 flight increased the mass flow rate of the air captured at the intake due to pre-compression effect of the nose shockwave, also increasing the thrust obtained at the engine plug nozzle. Sufficient thrust for acceleration were obtained at $\alpha=3$ and 5 degrees. Increase of flight Mach number at $\alpha=0$ degrees resulted in decrease of mass flow rate captured at the engine intake, and thus decrease in thrust at the nozzle. The thrust was sufficient for acceleration at M=3.5 and lower cases. Lift force on the aircraft was increased by the integration of engine on the aircraft for all varying angles of attack or flight Mach numbers. However, the slope of lift increase when increasing flight Mach number showed decrease as flight Mach number reach to M=5.0, due to the separation shockwave at the upper surface of the aircraft. Pitch moment of the aircraft was not affected by the installation of the engines for all angles of attack at M=5.0 condition. In low Mach number cases at $\alpha=0$ degrees, installation of the engines increased the pitch moment compared to no engine configuration. Installation of the engines increased the frictional drag on the aircraft, and its percentage to the total drag ranged between 30-50% for varying angle of attack in M=5.0 flight.

• 분석과학
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• 제8권4호
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• pp.715-722
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• 1995

The structural characterization for series of polyesters has been done by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Polymer fragments and intact oligomers composed of large numbers of repeat units have been investigated. Transesterification of polyesters in trifluoroacetic acid (TFA) and chlorodifluoroacetic acid (CFA) was monitored and reaction products were identified using TOF-SIMS. The shapes and intensities of clusters in transesterification spectra show good agreement with the theoretical isotope pattern. TOF-SIMS spectra were used to obtain information about the progress of the transesterification reaction.

• 한국추진공학회지
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• 제24권6호
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• pp.16-27
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• 2020

넓은 비행영역에서 스크램제트 엔진의 운용을 위해, 비행 조건의 변화에도 안정적인 성능을 나타내는 흡입구의 설계가 중요하다. 본 연구에서는 마하수 4~6, 받음각 -6도~6도의 넓은 비행영역에서 안정적인 성능을 얻기 위한 2D 고정형 흡입구의 설계 방법에 대한 연구를 수행하였다. 설계 방법 및 설계 주안점에 대해 제시한 후, 넓은 비행영역에서 높은 전압력 회복율과 유량 포획율을 갖는 흡입구를 설계함에 있어 가장 중요한 설계요소인 초기 압축각도와 비행 마하수 설계점에 따른 성능예측 및 분석을 수행하였다. 분석 결과를 바탕으로 넓은 비행영역에서 안정적인 성능을 나타내기 위한 두 가지 주요 설계요소의 선정기준을 제시하였다.

• 한국추진공학회지
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• 제19권3호
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• pp.65-72
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• 2015

본 연구에서는 이중램제트 엔진 및 로켓/터빈 기반 복합사이클 엔진에의 활용을 위해 Mach 3에서부터 Mach 8까지 넓은 마하수 영역에서 적용이 가능한 초음속흡입구의 형상설계를 수행하고 그 설계방법론에 대해 고찰하였다. 축대칭 가변흡입구를 기본 개념으로 중심콘 각도 및 경사충격파 각도를 이용한 기하학적 관계식으로부터 흡입구 형상을 설계하였으며, 100%에 준하는 포획면적비를 갖도록 하였다. 또한 전산해석결과로부터 Mach 3~8까지 조건에서 흡입구 중심콘에서 발생한 충격파가 올바르게 배치되는 것을 확인하였다.