• Journal of Advanced Navigation Technology
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• v.11 no.4
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• pp.454-460
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• 2007

In this paper, we implemented a ray-tracing simulator with a ray-launching technique and generated the propagation path of each ray in an multiple-wall indoor environment. In this simulator, we adopted two dimension ray-tracing techniques considering the reflection and penetration were dominant propagation factor in the indoor channel. From the result, we verified that this ray-tracing simulator shows the similar pattern and delay distribution with the experiment results of the previous research.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.74-77
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• 2001

The impact response and damage of CLAS panel was investigated experimentally. The facesheet material used was RO4003 woven-glass hydrocarbon/ceramic and the core material was Nomex honeycomb with a cell size of 3.2mm and a density of 96 kg/$\textrm{m}^{3}$. The shield plane used was RO4003 and 2024-T3 aluminum. Static indentation and impact test was conducted to characterize the type and extent of the damage observed in two CLAS panels, and the performance of antenna used in a wireless LAN system. Correlation of peak contact force, residual indentation and the delamination area shows impact damage of the panel with an aluminum shield plane is larger than that of the panel with RO4003 shield plane, although tile former is more penetration resistant. The damage was observed by naked eye, ultrasonic inspection and cross sectioning. The shape and size of delamination was estimated by ultrasonic inspection, and the area of delamination linearly increases as impact energy increases. The performance of impact damaged antenna was estimated by measuring return loss and radiation pattern.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.8
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• pp.1138-1144
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• 2002

Recently GDI(Gasoline Direct Injection) engine is spot-lighted to achieve higher thermal efficiency under partial loads and better performance at full loads. To realize this system, it is essential to make both stratified combustion and homogeneous combustion. Spray pattern must be optimized according to injection timing because ambient pressure in combustion chamber is varied with crank angle. In this experimental study, two types of visualization system such as laser scattering method and schlieren method were developed to clarity the spray behavior during on intake stroke. As the ambient pressure increases, thepenetration length and spray angle show a tendancy to decrease due to rising resistance caused by the drag force of the ambient air. Distribution of injected fuel on intake stroke has a significant effect on homogeneous mixture in the cylinder. These results provide the information on macroscopic wall-wet growth in the cylinder and design factors for developing GDI injector.

• Journal of ILASS-Korea
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• v.16 no.1
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• pp.7-14
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• 2011

High pressure LPG fuel spray with a conventional swirl injector was visualized and the impact of the injection pressure was also investigated using a DISI (direct injection spark ignition) LPG single cylinder engine. Engine performance and emission characteristics were evaluated over three different injection pressure and engine loads at an engine speed of 1500 rpm. The fuel spray pattern appeared to notably have longer penetration length and narrower spray angle than those of gasoline due to its lower angular momentum and rapid vaporization. Fuel injection pressure did not affect combustion behaviors but for high injection pressure and low load condition ($P_{inj}$=120 bar and 2 bar IMEP), which was expected weak flow field configuration and low pressure inside the cylinder. In terms of nano particle formation the positions of peak values in particle size distributions were not also changed regardless of the injection pressure, and its number densities were dramatically reduced compared to those of gasoline.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1719-1728
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• 2017

Recent concerns about environmental conditions have triggered the growing interest in using green energy resources. These sources of energy, however, bring new challenges mainly due to their uncertainty and intermittency. In order to alleviate the concerns on the penetration of intermittent energy resources, this paper investigates impacts of realizing demand-side potentials. Among different demand-side management programs, this paper considers demand response wherein consumers change their consumption pattern in response to changing prices. The research studies demand response potentials from different load sectors on generation system well-being. Consumers' sensitivity to time-varying prices is captured via self and cross elasticity coefficients. In the calculation of well-being indices, sequential Monte Carlo simulation approach is accompanied with fuzzy logic. Finally, IEEE-RTS is used as the test bed to conduct several simulations and the associated results are thoroughly discussed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.11
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• pp.1455-1462
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• 2018

As the interests in eco-friendly energy has increased, the interests in Electric Vehicles(EVs) are increasing as well. Moreover, due to the government's economic support for EVs, penetration level of it has rapidly increased. These sharp increases, however, induce various problems in distribution system, such as voltage/frequency variations, peak demand increasement, demand control, etc. To minimize these possible matters, lots of research have conducted. Nevertheless, most of it assumed extremely important factors, such as numbers and charging patterns of EVs. It inevitably results in errors in their research, and thus make it difficult to prevent the possible matters from EVs. In this paper, therefore, we use actual EVs charging data from KEPCO, and analysis and deduction of it were conducted. The simulations were carried out for four aspect(season, region, purpose).

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.664-670
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• 2010

The study on mechanical behavior of the structure at the site includes experimental method and numerical analysis method. Experimental method is categorized into true-scale test and laboratory model test. A laboratory model test is to monitor the failure mechanism with a model simulated similar with a real ground so as to identify the quantitative result, while a true-scale model test is the approach which enables to identify the potential problems that may occur with a simulated construction situation similar with a real site circumstance. Thus this study was intended to carry out the experimental test of non open-cut excavation by pipe roof method which is mostly common in domestic sites. as well as was aimed at identifying the ground behavior occurred during pipe penetration using laboratory model test. Appropriate reduced-scale model was selected, taking into account of domestic geological characteristics and operation characteristics of traditional and high-speed rail trains and the qualitative evaluation of displacement was carried out based on a certain ground loss volume depending on excavation after categorizing trackbed settlement pattern by depth of top soil.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.4
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• pp.134-140
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• 2009

The feasibility of electrochemical drilling and milling on stainless steel are investigated using tungsten microelectrode with $10{\mu}m$ in diameter. For the development of environmentally friendly and safe electrochemical process, citric acid solution is used as electrolyte. A few hundred nanoseconds duration pulses are applied between the microelectrode and work material for dissolution localization. Tool fracture by Joule heating, micro welding, capillary phenomenon, tool wandering by the generated bubbles are observed and their effects on micro ECM are discussed. Occasionally, complex textures including micro pitting corrosion marks appeared on the hole inner surface. Metal growth is also observed under the weak electric conditions and it hinders further dissolutions for workpiece penetration. By adjusting appropriate pulse and chemical conditions, micro holes of $37{\mu}m$ in diameter with $100{\mu}m$ in depth and 26Jim in diameter with $50{\mu}m$ in depth are drilled on stainless steel 304. Also, micro grooves with $18{\mu}m$ width and complex micro hand pattern are machined by electrochemical milling.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.7 s.172
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• pp.62-70
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• 2005

The nanoindenter and AFM have been used for nanofabrication, such as nanolithography, nanowriting, and nanopatterning, as well as measurement of mechanical properties and surface topology. Nanoscale indents can be used as cells for molecular electronics and drug delivery, slots for integration into nanodevices, and defects for tailoring the structure and properties. Therefore, it is very important to make indents of desired morphology (shape, size and depth). Indents of different shapes can be obtained by using indenters of different geometries such as a cube comer and conical and spherical tips. The depth and size of indents can be controlled by making indentations at different indentation loads. However, in case of viscoplastic viscoelastic materials such as polymethylmethacrylate (PMMA) the time dependent deformation (TDD) should also be considered. In this study, the effect of process parameters such as loading rate and hold-time at peak load on the indent morphology (maximum penetration depth, elastic recovery, transient creep recovery, residual depth pile-up height) of PMMA were studied for hyperfine pattern fabrication.

• Journal of ILASS-Korea
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• v.12 no.4
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• pp.204-210
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• 2007

The worldwide energy problem and global warming cause the need of alternative fuels which feature low carbon-dioxide emission and another energy source. Liquefied Petroleum Gas (LPG) is one of the alternative fuels widely used as domestic and transportational fuel. The third generation LPLi fuel supply system has merits in the increase of engine power and low emissions. The injectors used in LPLi system should overcome a leakage problem and satisfy the durability conditions. Therefore, 1000 hour durability test of the injectors was carried out throughout this research. First, the spray pattern and the penetration length of the selected injectors is graphically shown. Next, the leakage amount with respect to the injection cycle is introduced. Finally, the shapes of nozzle holder and nozzle tip after durability test was investigated by analyzing the microscopic image of the injector tip. The variation in the shape of nozzle tip mainly due to the residue of rubber materials is found to be the reason for leakage.