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플랜지 케이스의 입구온도 경계조건에 따른 케이스 내부의 열적거동에 관한 연구
고동국,명순식,강병용,김민수 한국기계기술학회 2019 한국기계기술학회지 Vol.21 No.5
In this study, the thermal behavior characteristics of flange case interior were analyzed by the numerical method. The boundary conditions at the inlet port of flange case were the heat flux and heat flux time. As the heat flux time at inlet of case increased, the temperature values gradually increased, and the degree of increase was very small. If the heat flux of the melted iron increases to 2,000,000W/m2, the temperature change at the case interior will occur largely, causing heat deformation. As a result, in order to reduce thermal defects at the case interior, the heat flux and heat flux time of the melted iron should be set within 500,000W/m2 and 5 seconds, respectively.
태양열 집열면이 있는 4각 덕트 내의 열전달 특성에 관한 연구
고동국,조대진,윤석주,박상규 대한설비공학회 2002 설비공학 논문집 Vol.14 No.12
This paper analyzed the characteristics of heat transfer in quadangle duct with absorber plate by solar radiation. Effects o( Reynolds number on increasing temperature at outlet for variation of absorber plate temperature were analyzed by using numerical analysis technique. And also the effects of turbulent intensity of inlet flow on increasing temperature at outlet for various duct height and effects of inlet aspect ratio of quadrangle duct and position of heating surface on the outlet temperature were analysed. As the results, Outlet temperature was greatly influenced in low Reynolds number. And the highest outlet temperature distribution appeared on the inlet aspect ratio 2 because of the buoyancy effect.
태양열 온풍기내부의 집열면 조건이 덕트 출구 공기의 온도에 미치는 영향
고동국 한국기계기술학회 2015 한국기계기술학회지 Vol.17 No.3
This paper analyzed air temperatures at outlet according to condition of absorber plate of the solar air heater. Effects on air temperature at outlet of duct according to absorber plate temperature were analyzed by using numerical analysis technique. And also the effects on air temperatures at outlet were analysed by the height and position of absorber plate. As the results, air temperatures at outlet of duct was small influenced in velocity 5 m/s of inlet according to absorber plate temperature. And the highest outlet average temperature distribution appeared at the height of 2 cm and the bottom absorber plate of duct at the inlet aspect ratio 2.
태양열 온풍기내부의 집열면 조건이 덕트 출구공기의 온도상승에 미치는 영향
고동국 한국기계기술학회 2015 한국기계기술학회지 Vol.17 No.3
This paper analyzed the increasing air temperature at outlet according to condition of absorber plate of the solar air heater. Effects on the increasing air temperature at outlet of duct according to absorber plate temperature were analyzed by using numerical analysis technique. And also the effects of the height and position of absorber plate on increasing temperature at outlet were analysed. As the results, Outlet air temperature was small influenced in velocity 5m/s of inlet according to absorber plate temperature. And the highest outlet average temperature distribution appeared at the height of 2cm and the bottom absorber plate of duct at the inlet aspect ratio 2.
실링 챔버내 유로형상이 탄소섬유의 탄화공정에 미치는 영향에 대한 연구
고동국,압드엘모타립 하마다,이교우,임익태 한국기계기술학회 2021 한국기계기술학회지 Vol.23 No.6
This paper studies the flow characteristics inside the low-temperature carbonization(LTF) including sealing chamber with labyrinth. The flow behavior inside the furnace was analyzed according to different labyrinth shapes. The effects of labyrinth baffle number, and clearance between upper and lower baffles in the sealing chamber were investigated. The large vortex and stagnation region are generated in the chamber when the gap between the baffle and baffle is small. As a result, the gas discharge flow rate can be increased by 29.4% when the flow space of labyrinth is made 75% of the baffle length.
타이어 몰드 표면에서의 열유속 및 열전달 시간에 따른 몰드의 온도분포에 관한 수치해석 연구
고동국,갈준총,김민수 한국기계기술학회 2016 한국기계기술학회지 Vol.18 No.6
In this study, we designed the 3-dimensional tire mold according to the A automobile company’s tire model, and analysed the distribution of temperature of mold using the numerical method when the heat flux and heat transfer time at the surface of tire mold were changed. A analysis region of mold was the 1/16 of entire mold, and the grid number was about more than 880 thousand. In order to analyze the temperature change of mold, the thinnest part of the mold was chosen as the research object, and then the temperature of 6 points on the vertical downward direction of the thinnest part was analyzed with the time change. While the numerical condition was that heat flux was 321,200 W/m2, 440,000 W/m2 and 880,000 W/m2, and measuring time was 0.1 second, 0.2 second, 0.5 second and 1 second, respectively. As a result, the temperature difference between the surface temperature and the lowest temperature of mold was 7.3℃ when the heat transfer time was 0.1 second. Also, the minimum temperature difference was almost 0.11℃ when the heat transfer increased to 1 second. It can be explained that the main material of tire mold was aluminum and its thermal conductivity was high (k=140 W/m·K). In addition, when the heat transfer time was more than 1 second, the heat flux of mold surface will be transmitted at the inside of the thinnest part, and the heat transfer will be a marked difference according to the shape of the thinnest part.
위성통신을 위한 강인한 TDMA Frame 구조 및 초기동기 기법
고동국,윤원식,Ko, Dong-Kuk,Yoon, Won-Sik 한국정보통신학회 2012 한국정보통신학회논문지 Vol.16 No.8
위성통신에서 이용 효율을 높이기 위해 Time division multiple access (TDMA)를 사용하였으며, 대표적으로 Digital Video Broadcasting- Satellite Second Generation (DVB-S2) 등으로 표준화되어 운용되어 왔다. 본 논문에서는 이미 표준화된 DVB-S2를 직접 사용하기 어려운 특수한 용도의 시스템이 필요하였고, 이를 위하여 다소 주파수 운용효율 저하를 감수하더라도 열악한 전파환경에서도 신뢰성있게 운용이 가능한 TDMA 프레임 구조를 연구하였다. 프레임 주기가 12초로 수~수십 msec인 일반적인 TDMA 시스템 프레임 구조와 차이가 많고, 이에 따른 시간 및 주파수 드리프트 등을 고려하였다. 그리고 주파수 옵셋이 25 kHz이고 낮은 Signal To Noise Ratio(SNR) 에서도 초기 타이밍 동기 및 주파수와 페이저 초기 동기를 확보하는 방식을 제시하였다. 이를 검증하기 위하여 시뮬레이션 및 연동시험을 수행한 결과 SNR -2.5 dB에서도 안정적으로 동기가 확보됨을 알 수 있다. A TDMA system in satellite communication has been utilized. Especially DVB-S2 was standardized and now operated in satellite broadcasting system. In this paper, we propose a TDMA frame structure appropriate for special purpose which has the good reliablilty in a poor RF environment even if frequency efficiency is decreased. TDMA frame duration is 12 seconds which is long duration in comparison with general TDMA system with several ms. Designing the frame structure, time and frequency shift in single frame duration are considered. Simulation results show that the proposed frame structure and synchronization method has robust synchronization performance when the terminal is even in low SNR as well as 25 kHz frequency offsets.
탄소섬유용 저온 탄화로 내의 배출가스 및 열유동에 대한 수치해석 모델링
고동국,자헤르 라마단,김민우,이교우,임익태 한국기계기술학회 2023 한국기계기술학회지 Vol.25 No.3
In this study, numerical modeling on the gas flow and off-gases in the low temperature carbonization furnace for carbon fiber was analyzed. The furnace was designed for testing carbonization process of carbon fibers made from various precursors. Nitrogen gas was used as a working gas and it was treated as an incompressible ideal gas. Three-dimensional computational fluid dynamics for steady state turbulent flow was used to analyze flow pattern and temperature field in the furnace. The off-gas mass fraction and cumulative emission gas of species were incorporated into the CFD analyses by using the user defined function(UDF). As a results, during the carbonization process, the emission of CO2 was the dominant among the off-gases, and tow moving made the flow in the furnace be uniform.