• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1674-1680
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• 2002

An experimental study was made of a large-scale vortical structure over a backward-facing step. The Reynolds number based on the step height was R $e_{H}$ =33,000. To recognize the large-scale vortex, three components of velocity were measured. The measurements were performed in the recirculation zone (x/H=4.0) and the reattachment zone(x/H=7.5). To measure the wall pressure fluctuations in a turbulent flow over a backward-facing step, a 32-channel microphone array was installed beneath the wall in the streamwise and spanwise directions. From the measured pressure field, the size of large-scale vortex was obtained. As a detailed study, a conditionally-averaging technique was employed to characterize the coherent structure of the large-scale vortex. To see the relationship between the flow field and the relevant spatial mode of the pressure field, the spatial box filtering (SBF) was examined. A cross-correlation between velocity and pressure fluctuations was performed to identify the structure and the length scale of the large-scale vortex.x.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.2
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• pp.237-246
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• 1999

A miniaturized waveguide bandpass filter is designed by combining a corrugated lowpass structure and a highpass configuration based on the cut-off effect of waveguides. It is smaller than the conventional waveguide bandpass filter composed of half-wavelength resonators and has wider spurious free characteristics. Optimized design data for a seven-order waveguide bandpass filter with the symmetrical structure are given at the center frequency of 10 GHz with 800 MHz bandwidth. Measured bandwidth of the center frequency of 9.97 GHz is 840 MHz and measured insertion loss is 0.97dB, The length of the bandpass filter is 64.38mm. The first spurious response is produced at 26.1 GHz.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.6
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• pp.17-23
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• 2021

In the present study, a more compact dual-band slot antenna is newly proposed for Wi-Fi application. The proposed antenna is composed of rectangular two stepped slot with open end which can generate standing wave resonance at dual frequency bands and L-type microstrip feed line. The measured impedance bandwidths are 50 MHz(2.412 ~ 2.470 GHz) at low frequency band and 452 MHz(5.451 ~ 5.903 GHz) at high frequency band respectiviely. Furthermore its size of 14 × 21 mm² is reduced by 30% compared to the size of 20 × 21 mm² of a conventional similar compact slot antenna. It has the omni-directional radiation pattern characteristics of a typical dipole antenna on the H-Plane, so it is suitable for commercial wireless network applications such as Wi-Fi.

• Journal of the Korea Society of Computer and Information
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• v.25 no.12
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• pp.243-251
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• 2020

This study is intended to verify the efficiency of the information system by using the navigation application in case of fire. In the demonstration scenario simulation, it was assumed that a fire occurred 6th floor in Korea Institute of Industrial Design Promotion located in C city, K province. Eighty juniors students from K University's department of paramedics of science participated. As a result of the experiment, the demonstration simulation using the navigation application showed that the evacuation time was faster than the case of evacuation guidance in a fire situation. The need for a fire prevention system and fire prevention awareness before and after the implementation of the demonstration scenario simulation increased the need for a fire prevention system and fire prevention awareness score after the experiment.

• Journal of Advanced Navigation Technology
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• v.26 no.2
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• pp.99-104
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• 2022

Recently, the domestic demand for weapon systems based on aircraft platforms is gradually increasing. In particular, the demand for effective precision guided missile(PGM) which cruises for several hundred kilometers after launch to strike the ground target is rising drastically, but it is in the early stages of development, and research based on it are limited. This paper is a study on the power converter unit(PCU) within PGM which is mounted on an aircraft platform based on MIL-STD-1760, which is an interface between an aircraft and PGM. We investigated the electrical properties and structure of the umbilical connector, and the aircraft/store electrical interconnection system. Also, the focus on the design specifications of the PCU that supplies power were described. This result 3 phase AC input, which is the state for the guided simulation power supply in the state of being mounted on an aircraft that rectification method with power factor correction(PFC) compared to bridge rectifier circuit. In the future, it may be used as a basis for power supply design on aircraft mounted weapon systems.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1998.06a
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• pp.81-85
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• 1998

점확산 함수(point spread function; PSF)의 정확한 추정은 복원결과가 원 영상에 얼마나 근접할 수 있는가를 결정한다는 점에서 영상처리의 중요한 연구 주제중의 하나가 된다. 본 논문에서는 PSF를 추정하기 위한 알고리즘을 제안하고, 이를 영상복원에 적용한 후 이를 기반으로 디지털 자동초점시스템을 제안한다. 초점불안전 열화시스템을 구현하기 위한 과정은 두 단계로 구성되어 있는데, 즉 입력 영상에서 에지분류를 통한 PSF 추정과, 이를 이용한 영상복원이다. 보다 구체적으로, 입력 영상에 특정 에지가 있는 임의의 크기의 블록을 선정해부면, 그 블록으로부터 자동으로 에지방향이 기저영상을 이용해서 구해지며 확산원의 크기를 추정하여 1차원 단위 계단응답과 영역을 구하여 평균한 후, 2차원 등방성 PSF를 추정한다. 마지막으로 추정된 PSF를 사용하여 복원을 수행함으로써 초점이 맞는 영상을 구한다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.453-462
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• 1994

Variation of seismic wave field in a multi-layered attenuating elastic half space is studied by the propagator matrix method and point source models of which fault-slip functions are defined as ramp functions. In this paper, the earth is modeled as being composed of horizontally stratified layers, with uniform material properties for each layer. The partial differential equations for the seismic motion in each layer are solved using a Fourier Hankel transform approach. Time histories and frequency contents of accelerations and displacements due to a vertical dip-slip and strike-slip point source located in the underlain half space are calculated at the layer interfaces using the developed programs and their characteristics are represented.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.2
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• pp.218-225
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• 2015

Inverse synthetic aperture radar(ISAR) is coherent imaging system formed by conducting signal processing of received data which consists of radar cross section(RCS) reflected from maneuvering target. A novel algorithm is proposed to compensate inter-pulse motion(IPM) for the purpose of forming an well-focused ISAR image through signals generated by stepped chirp waveform( SCW). The velocity and acceleration of the target related to IPM are estimated based on particle swarm optimization (PSO) which has been widely used in optimization technique. Furthermore, a modified PSO which enables us to improve the performance of PSO is used to compensate IPM in a very short-time. Simulation results using point scatterer model of a Boeing-737 aircraft validate the performance of the proposed algorithm.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.2
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• pp.18-31
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• 2018

It is important to conduct various analyzes to evacuate occupants in advance, because the disaster can cause serious injury. Therefore, it is necessary to analyze all the predictable scenarios that may occur. In this study, we propose a method to analyze the evacuation of indoor disaster using activity - based transport model MATSim. We have developed the university building as target area and simulated about 5,000 occupants. The analysis scenarios are set as basic evacuation conditions, exit closures and emergency stair closures. As a result of analysis of each scenario, the evacuation time was analyzed to be about 5:40(340s) in the base scenario, increased by 15% in the scenario 2 and increased by 23% in scenario 3. As a result of this study, we suggest that it is important to manage illegal obstacles of emergency stairs for rapid evacuation. Therefore, this study can contribute to the effective disaster prevention strategy of the building.

• Korean Journal of Optics and Photonics
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• v.15 no.6
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• pp.531-538
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• 2004

Studies of adsorption isotherms with sharp step-wise layer condensation help us to better understanding of two dimensional layers. For this, an adsorption isotherm apparatus, using a phase modulated ellipsometric technique, has been constructed and an adsorption experiment has been performed. With subatomic scale resolution(∼0.3 $\AA$), the adsorption processes could be observed by ellipsometric signals. On measurement of multilayer adsorption of argon on highly oriented pyrolytic graphite(HOPG), thousands of adsorbed layers were observed at 34.04 K, which suggests that the adsorption is completely wet. On the contrary nine sharp layers of steps for adsorptions and desorptions were observed at 67.05 K. These isotherms obtained can provide a lot of information about thermodynamic states, bonding energies between adsobate and substrate, and structure transitions in the adsorbed film.