• Journal of the Korean Institute of Gas
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• v.15 no.3
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• pp.31-38
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• 2011

In this study, we investigate simulation studies to confirm the removal of smoke through ventilation when the subway car is on fire and stopped in an underground subway tunnel, by using Fire Dynamics Simulator (FDS) which is being upgraded by NIST. The structure of subway tunnel and train for simulation modeling are based actual data from Seoul metropolitan subway. The main purpose of this study is to assure the removal efficiency of the ventilation when changing the ventilation capacity between 2.0 m/s and 3.0 m/s. The results of the study shows that carbon monoxide (CO) and carbon dioxide ($CO_2$) are reduced by about 35% as the ventilation capacity is increased by 0.5 m/s. This study also performs the grid sensitivity verification of FDS for improved accuracy of the results. To find the effective size of the grid, three cases are simulated and the results are compared.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.53-59
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• 2010

This research aims in finding a more optimal ejector size for evacuating engine exhaust gasses and 20% of the cell cooling air. The remaining 80% of cell cooling air pumped into the test chamber is separately exhausted from the test chamber via a discharge port fitted with flow control valves and vacuum pump. Unlike its predecessor this configuration utilizes a smaller capture area to improve pressure recovery. The modified ejector size has a diameter of 1100mm enough to evacuate 66kg/s jet engine exhaust in addition to about 20%, 24kg/s of the cell cooling air tapped from the sterling chamber. This configurations has an area ratio of the engine exit and ejector inlet of about 1.2. Simulation results of the proposed ejector configuration, indicates improved pressure recovery.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.101-104
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• 2010

Recently, needs for UAVs and small aircraft and small turbo jet or turbo fan engines for these air-crafts are increasing. Size and weight are the two main restrictions in small air-crafts such as UAV or VLJ propulsion system applications. Therefore, high power density is required in small size and designers come up with unconventional solutions in the design of small aero gas turbine engines. One of the solutions is the usage of highly loaded axial compressors. This paper introduces an aerodynamic design method of a highly loaded axial compressor and its review process. Numerical simulation has been carried out to assess the aerodynamic performance of the compressor.

• Journal of KIISE:Databases
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• v.31 no.4
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• pp.384-394
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• 2004

Recently, to relieve the performance degradation caused by the bottleneck between CPU and main memory, cache conscious multi-dimensional index structures have been proposed. The ultimate goal of them is to reduce the space for entries so as to widen index trees and minimize the number of cache misses. The existing index structures can be classified into two approaches according to their entry reduction methods. One approach is to compress MBR keys by quantizing coordinate values to the fixed number of bits. The other approach is to store only the sides of minimum bounding regions (MBRs) that are different from their parents partially. In this paper, we propose a new index structure that exploits the properties of the both techniques. Then, we investigate the existing multi-dimensional index structures for main memory database system through experiments under the various work loads. We perform various experiments to show that our approach outperforms others.

• Korean Journal of Environmental Agriculture
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• v.27 no.2
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• pp.150-155
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• 2008

This study was carried out to determinate the location and the number of air inlet and outlet, optimum air inlet velocity for effective ventilation in windowless weaning piglet house($2.90(W){\times}9.90(L){\times}2.80(H)$ m) by CFD(Computation Fluid Dynamics) simulation. The weaning piglet house for this experiment was consisted of 11 air inlets and 9 outlets, modified and simulated using CFD code, FLUENT. The simulation result for the original weaning piglet house, which was not modified, showed ununiform ventilation for each room. Therefore, for uniform ventilation, 4 air inlets and 1 outlet were completely closed, and 2 air outlets were partially closed. The simulation result for the modified weaning piglet house showed uniform ventilation for each room and the optimum air inlet velocity of 0.5 $m\;sec^{-1}$.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.3
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• pp.269-285
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• 2014

In spite of the importance of the natural ventilation pressure(NVP) in tunnels for the optimal design of the ventilation system, there have been only few studies on the NVP because its measurement and quantitative analysis are not straightforward. This study aims at quantifying the amount of the NVP with the terrain and meteorological data for the local major tunnels. And ultimately this will lead to developing the guidelines for quantifying and applying NVP for the optimal design of tunnel ventilation system. 22 local tunnels in the major routes are studied for the NVP quantification. NVP derived from the meteorological data is in the range of 20~140 Pa, while NVP estimated from the terrain data ranges from 20 to 200 Pa. Since the jet fan pressure is about 10~15 Pa per unit, the minimum level of NVP expected in the local tunnels is larger than the pressure rise by one unit of the ordinary jet fan. This implies that NVP in local tunnels should be quantified and be taken into consideration for the economic and safe ventilation design. The barometric pressure difference between tunnel portals is found to be the most influential factor, accounting for 61% of the NVP, while the wind pressure acting on the portals and the chimney effects occupy 22% and 17%, respectively.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2017.04a
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• pp.78-78
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• 2017

현재 국내에 공급되고 있는 잡곡류 수확기는 보행형 예취기, 탈곡기 위주의 저능률 기계화 수준으로 고능률의 콤바인 수확기 개발이 필요하며, 특히 잡곡류가 소규모 경작지의 영세농가 위주로 재배되어 저가격의 소형 콤바인 수확기 개발이 절실히 요구되고 있다. 따라서 본 연구는 소규모 밭의 두류 및 잡곡 수확작업에 적응성이 뛰어나며, 농기계 임대사업소의 활용도를 높일 수 있고, 여성과 고령자도 쉽게 운전할 수 있어 수확작업의 노동력을 크게 절감할 수 있는 저가격의 25kW급 자주식 소형 콤바인을 개발하고자 시작기를 설계 제작하였다. 시작기의 주요부로 엔진은 25kW/2600rpm 3기통 디젤엔진을 탑재하였으며, 동력전달부는 주변속 3단, 부변속 2단의 선택맞물림 기어식의 변속장치를 이용하였다. 주행부는 궤도형으로 조향클러치와 습식 원판식 제동장치를 채용하였다. 전처리부는 선단거리 1700 mm의 디바이더와 상하좌우 수동 조절되는 회전속도 약 42 rpm의 정오각형 릴로 구성하였으며, 전처리부의 최대 승강높이는 740 mm이었다. 작물이송부는 돌기부착 오거와 체인컨베이어로 구성되어 있으며, 탈곡부는 단동형 축류식의 직경 440 mm, 길이 1180 mm의 급동과 높이 65 mm, 지름 10 mm의 46개 강봉형 급치, 격자형 수망으로 구성하였으며, 회전속도는 약 325 rpm으로 작동하도록 하였다. 선별 정선부는 요동 송풍선별식으로 곡립판, 볏짚체, 곡립체, 송풍팬으로 구성하였고 송풍팬의 회전속도는 약 850 rpm, 요동진동수는 약 5.8 Hz로 작동하도록 하였다. 곡물이송부와 재처리부는 수평이송 외경 103 mm, 수직이송 외경 110 mm의 피치가 모두 82 mm인 스크류컨베이어를 이용하였으며, 곡물탱크는 용량이 250 로 2개의 배출구로 곡물을 포대에 담도록 하였다. 그 외 시작기는 운전조작부, 유압장치부, 전기장치부 등을 갖도록 설계 제작하였다. 전체적인 기체의 크기는 길이${\times}$폭${\times}$높이 $3935{\times}1900{\times}2440mm$이었으며, 기체 중량은 약 1753 kg이었다. 콩 대상 기초 성능시험 결과 시작기의 작업속도는 약 0.5 m/s, 작업능률은 약 11 a/h로 나타났다.

• Journal of Aerospace System Engineering
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• v.14 no.1
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• pp.68-73
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• 2020

This purpose of this paper was to review the development trend of the VTOL MAVs with a ducted propellant that can fly like the VTOL at intermediate and high speeds, hovering, landing, and lifting off vertically over urban areas, warships, bridges, and mountainous terrains. The MAV differs in flight characteristics from helicopters and fixed wings in many respects. In addition to enhancing thrust, the duct protects personnel from accidental contact with the spinning rotor. The purpose of the U.S. Army FCS and DARPA's OAV program is spurring development of a the VTOL ducted MAV. Today's MAVs are equipped with video/infrared cameras to hover-and-stare at enemies hidden behind forests and hills for approximately one hour surveillance and reconnaissance. Class-I is a VTOL ducted MAV developed in size and weight that individual soldiers can store in their backpacks. Class-II is the development of an organic VTOL ducted fan MAV with twice the operating time and a wider range of flight than Class-I. MAVs will need to develop to perch-and-stare technology for lengthy operation on the current hover-and-stare. The near future OAV's concept is to expand its mission capability and efficiency with a joint operation that automatically lifts-off, lands, refuels, and recharges on the vehicle's landing pad while the manned-unmanned ground vehicle is in operation. A ducted MAV needs the development of highly accurate relative position technology using low cost and small GPS for automatic lift-off and landing on the landing pad. There is also a need to develop a common command and control architecture that enables the cooperative operation of organisms between a VTOL ducted MAV and a manned-unmanned ground vehicle.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.644-648
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• 2019

This study examined effects of the wall thermal conductivity coefficients on the thermal fluid phenomenon of a compartment fire. The reduced scale compartment was 0.4 m in width, 0.6 m in length and 0.6 m in height with a fire-board, which has a thermal conductivity coefficient of $0.18W/m{\cdot}K$. The local temperature at a 0.37 m height and the overall heat release rate were measured under the following experiment conditions: a $0.12m^2$ opening area and $0.01m^2$ pool size of a gasoline fire. The numerical results obtained by the Fire Dynamic Simulation were compared with the experimentally measured temperature. The deviations were within 10 % in the period of the steady state for maximum heat release rate (4.8 kW). The numerical results show that the average temperature of the compartment wall decreases by approximately 71 % with increasing thermal conductivity coefficient from $0.1W/m{\cdot}K$ to $100.0W/m{\cdot}K$ on the fixed heat release rate.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.1
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• pp.29-33
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• 2019

With shrinking form factor and improving performance of electronic packages, high input/output (I/O) density is considered as an important factor. Fan out wafer-level packaging (FO-WLP) has been paid great attention as an alternative. However, FO-WLP is vulnerable to warpage during its manufacturing process. Minimizing warpage is essential for controlling production yield, and in turn, package reliability. While many studies investigated the effect of process and design parameters on warpage using finite element analysis, they did not take uncertainty into consideration. As parameters, including material properties, chip positions, have uncertainty from the point of manufacturing view, the uncertainty should be considered to reduce the gap between the results from the field and the finite element analysis. This paper focuses on the effect of uncertainty of Young's modulus of chip on fan-out wafer level packaging warpage using finite element analysis. It is assumed that Young's modulus of each chip follows the normal distribution. Simulation results show that the uncertainty of Young's modulus affects the maximum von Mises stress. As a result, it is necessary to control the uncertainty of Young's modulus of silicon chip since the maximum von Mises stress is a parameter related to the package reliability.