• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.2
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• pp.10-16
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• 2012

A computational analysis of nozzle flow characteristics and plume structure is conducted to examine performance of the supersonic nozzle employed in a thruster for ground firing test. At first, flow simulations in two-dimensional converging-diverging nozzle are performed for the verification of computational capability as well as turbulence model validity. Axisymmetric converging-diverging nozzles for ground firing test are analyzed with the k-${\omega}$ SST model. A performance penalty caused by flow separation in a diverging section is observed in initially-designed nozzle. The performance could be enhanced by the modification of the diverging section of nozzle contour.

• Journal of Korean Society of Disaster and Security
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• v.8 no.1
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• pp.39-46
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• 2015

This study is concerned with the estimation of fluctuation wind velocity spectrum and turbulence characteristics in the major cities reflecting the recent meteorological with typhoon wind velocity about 2003 (Maemi) 2010 (Kompasu) 2012 (Tembin). The purpose of this paper is to present spectral analysis for longitudinal component fluctuating velocity obtained by Monte Carlo Simulation method. In the processes of analysis, the longitudinal velocity spectrums are compared widely used spectrum models with horizontal wind velocity observations data obtained at Korea Meteorological Adminstration (KMA) and properties of the atmospheric air for typhoon fluctuating wind data are estimated to parameters with turbulency intensity, shear velocity, probability distribution and roughness length.

• Journal of Energy Engineering
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• v.12 no.1
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• pp.11-16
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• 2003

A numerical study was performed on the transient fuel temperatures of a military aircraft stationed under non-operating static condition. Numerical calculation was peformed by an explicit method using modified Dufort-Frankel scheme. It was assumed that the non-operating aircraft is subjected to repeated daily cycles of air temperature with the solar radiation and wind speed corresponding to the 1 % hot day ambient condition. And, the aircraft was assumed to be in turbulent flow. The convective heat transfer coefficient for turbulent flow on the flat plate suggested by Eckert was employed to calculate heat transfer between the aircraft surface and the ambience. The energy conservation equation on fuel was used as governing equation for this analysis. As a result of this analysis, the wing tank temperature showed the highest temperature and the largest rate of temperature changes among fuel tanks. The results of this analysis could be used as initial foe] temperatures for analysis of the transient fuel temperatures in various flight missions. Also, this analysis method could be used to analysis and design of an aircraft thermal energy management system.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.20 no.1
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• pp.94-102
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• 2012

The aim of this paper is to research the change in the turbulent flow and the AOA occurred by $60^{\circ}$ crosswind to the direction of runway through the three-dimensional numerical analysis and to predict the take-off and landing flight stability. As a result, the maximum amplitude of AOA variation on runway reached $4.88^{\circ}$ within 7 second because of the wake formed by the constructions in the vicinity of the airport, and the overall effects appeared as an irregular aperiodic forms. Additionally, it was observed that the layout and shape of the buildings effected on the strength of turbulence directly, and the rapid flow generated between the buildings changed into stronger wake and eventually expected that the flow raises serious take-off and landing flight instability.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.17 no.4
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• pp.32-41
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• 2009

This paper presents the work being carried out in order to reduce the ground turbulence by the fence in the vicinity of airport runway. In preliminary study, we knows that cross-wind effect in the vicinity of runway is highly dependent on the shape of the buildings and have predicted results confirmed reduction of wind-effect by doing that set up the building with a fence, terraced shape or gap. This study is to figure out effect of ground turbulence by the building with fence, which is changing fence height, in using two-dimensional computational fluid dynamics analysis.

• Journal of Korean Society of Disaster and Security
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• v.6 no.2
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• pp.23-30
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• 2013

A dynamic analysis of random vibration processes is concerned with the first excursion probability based on first passage time during some specified lifetime or duration of the excitation. This study is concerned with the estimation of first-passage probability for hazard fluctuate wind velocity in the major cities reflecting the recent meteorological with largest data samples (yearly 2003-2012). The basic wind speeds were standardized homogeneously to the surface roughness category C, and to 10m above the ground surface. In this paper, the hazard fluctuate wind velocities are treated as a time-independent (stationary) random process and Gaussian random processes. The first excursion probability were calculated from Poisson model based on the independent event of level crossing & two-state Markov model based on the envelopes of level crossing.

• Journal of Space Technology and Applications
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• v.4 no.1
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• pp.48-61
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• 2024

In this paper, we introduce the concept of the cube satellite Chungnam National University Laser Unity Bus (CLUB), which can provide an integrated infrastructure for various ground-space laser applications. With the advent of the new space era, the rapid expansion of space utilization has begun to reveal the limitations of conventional radio frequencies. As space missions diversify, lasers are garnering attention as a viable alternative. Between ground and space, lasers are applied in various fields including satellite laser ranging (SLR), laser weapons, and laser communication. However, laser used between the ground and space are significantly influenced by the Earth's atmosphere. Consequently, understanding the atmospheric effects on laser propagation is crucial. In particular, atmospheric turbulence, which refracts and distorts laser beams, intensifies closer to the Earth's surface, exerting a greater impact on the uplink than on the downlink. While downlink verification is facilitated by ground detection, verifying the uplink poses challenges due to the necessity of space-based detection. In response to these challenges, we propose the idea of cube satellite as a means to enhance understanding and verification of laser propagation in the uplink. Additionally, we present the results of conceptual design by analyzing requirements, focusing on mission design of the CLUB cube satellite, following the stages of systems engineering for systematic cube satellite development.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.1
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• pp.265-276
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• 2018

Observation and data analysis techniques have been developed for observational blind areas in the lower atmosphere that are difficult to be monitored with fixed equipment on the ground. The vertical data of temperature and relative humidity are remotely collected by the UHF radiosonde installed on UAV and compared with the data measured in the 10 m weather tower. From the validated vertical profile, extrapolated surface temperature and the bulk transfer method were used to estimate the sensible heat flux depending on the atmospheric stability. Compared with the sensible heat flux measured by the 3-dimensional ultrasonic anemometer on the ground, the error of the sensible heat flux estimated was 23% that is less than the range of 30% allowed in the remote sensing. Estimated atmospheric boundary layer height from UAV sensible heat fluxes can provide useful data for air pollution diffusion models in real time and economically.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.6
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• pp.16-22
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• 2004

Unsteady vortex shedding behind a rectangular cylinder near a wall influences both increasing of drag and dynamic stability of heavy vehicle, bridge or building. Incompressible Averaged Navier-Stokes equation with modified ${\varepsilon}-SST$ turbulence model is adapted for investigating the flow field between the rectangular cylinder and the wall. In case the vortex shedding happens, not only the averaged maximum velocity is higher than other cases, but the position of the maximum velocity is closer to the lower surface of rectangular cylinder. On this study, it is confirmed that the vortex shedding behind a rectangular cylinder can be suppressed by the passive control method added by horizontal and vertical fences to the lower surface of rectangular cylinder.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.4
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• pp.67-74
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• 1999

Problems created by supersonic jet impinging on solid objects or ground arise in a variety of situations. For example multi-stage rocket separation, deep-space docking, V/STOL aircraft, jet-engine exhaust, gas-turbine blade, terrestrial rocket launch, and so on. These impinging jet flows generally contain a complex structures. (mixed subsonic and supersonic regions, interacting shocks and expansion waves, regions of turbulent shear layer) This paper describes experimental works on the phenomena (surface pressure distribution, flow visualization) when underexpanded supersonic jets impinge on the perpendicular, inclined plate using a supersonic cold-(low system. The used supersonic nozzle is convergent-divergent type, exit Mach number 2, The maximum on the plate when it was inclined was much larger than perpendicular plate, owing to high pressure recoveries through multiple shocks. Surface pressure distribution as to underexpanded ratio showed similar patterns together.