• Journal of Aerospace System Engineering
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• v.11 no.4
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• pp.22-29
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• 2017

A study is performed for the effective detection method of a fault which is occurred during operation in a small turbojet engine with non-linear characteristics used by unmanned air vehicle. For this study the non-linear dynamic model of the engine is derived from transient thermodynamic cycle analysis. Also for inducing real operation conditions the controller is developed associated with unscented Kalman filter to estimate noises. Sequential probability ratio test is introduced as a real time method to detect a fault which is manipulated for simulation as a malfunction of rotational speed sensor contaminated by large amount of noise. The method applied to the fault detection during operation verifies its effectiveness and high feasibility by showing good and definite decision performances of the fault.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.12
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• pp.1106-1112
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• 2005

An experimental investigation was performed to develop an empirical correlation of R-410A flowing through short tube orifices working near the critical region. Tests were executed by varying upstream pressure from 2,619 kPa to 4,551 kPa, and upstream subcooling from 2.8 and $11.1^{\circ}C$. The experimental data were represented as a function of major operating parameters and short tube diameter. As compared to mass flow trends at normal upstream pressures, flow dependency on upstream subcooling became more significant at high upstream pressures due to a higher density change. Based on the database obtained from this study and literature, an empirical correlation was developed from a power law form of dimensionless parameters generated by the Buckingham Pi theorem. The correlation yielded good agreement with the data. Approximately $92\%$ of the data were correlated within a relative deviation of $5\%$.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.29 no.1
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• pp.48-56
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• 2000

한국지역난방공사는 '87년 여의도에 최초 연공급을 시작한 이래 수도권 신도시 및 서울 강남 지역을 중심으로 지역난방 열공급을 지속적으로 확대하여 왔다. 안정적이고 경제적인 역공급을 위하여 분당, 고양 및 중앙의 CHP를 중심으로 연계배관망을 구성하였으며 '98년 기준 수도권 연계 공급량이 총 공급량의 61%를 차지하게 되었다. 또한 장기적으로 본 공사는 열공급의 신뢰성 및 경제성 향상을 위하여 급열센타 설치를 비롯하여 종합적인 네트워크를 구성하여 운영할 계획이며 분당과 고양의 CHP를 기저부하로 삼아 피크수요를 감당할 소규모 분산형 열원을 설치하여 수도권 열공급을 확대하여 전 수도권을 지역난방 배관으로 네트워크화할 계획을 가지고 있다. 따라서, 구체적인 세부계획을 수립하기 위하여는 수도권 네트워크 사업의 장기적인 경제성 분석이 필수적이며 이러한 분석은 기존의 열원 및 열배관시설은 물론 향후 건설될 열원 및 배관, 수요개발전망 등 제반요소를 고려하여 종합적으로 이루어져야 하다. 본 연구는 이에 앞서 분당과 일산CHP를 독립된 수용범위를 갖는 열원으로 간주하여 각각의 CHP를 중심으로 열공급량의 증가에 따라 피크용 열원인 HOB 건설을 증가시킬때의 경제성을 그 대상으로 하여 기본적인 모델을 제시하고 대략적인 추세를 파악하고자 하였다. 데이터는 본 공사 고양지사와 분당지사의 '98 운영실적으로 기준으로 하였으며, 수도권 전체 네트워크를 대상으로 하는 실제 경제성 분석은 다음 과제로 계속 추진될 것이다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.102-111
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• 2000

A numerical model which simulates the simultaneous heat and mass transfer within a vertical tube GAX absorber was developed. The ammonia vapor and the solution liquid are in counter-current flow, and the hydronic fluid flows counter to the solution liquid. The film thickness and the velocity distribution of the liquid film were obtained by matching the shear stress at the liquid-vapor interface. Two-dimensional diffusion and energy equations were solved in the liquid film to give the temperature and concentration, and a modified Colburn-Drew analysis was used for the vapor phase to determine the heat and mass fluxes at the liquid-vapor interface. The model was applied to a GAX absorber to investigate the absorption rates, temperature and concentration profiles, and mass flow rates of liquid and vapor phases. It was shown that the mass flux of water was negligible compared with that of ammonia except the region near the liquid inlet. Ammonia absorption rate increases rapidly near the liquid inlet and decrease slowly. Both the absorption rate of ammonia vapor and the desorption rate of water near the liquid inlet increase as the vapor mass flow rate increases, but the mass fluxes of the ammonia and the water near the liquid outlet decrease as the mass flow rate of the vapor increases.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.29 no.2
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• pp.94-99
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• 2021

UTM is an air traffic management ecosystem under development for autonomously controlled operations of UAS by the FAA, NASA, other federal partner agencies, and industry. They are collaboratively exploring concepts of operation, data exchange requirements, and a supporting framework to enable multiple UAS operations beyond visual line-of-sight at altitudes under AGL 500ft in airspace where air traffic services are not provided. Minimum Safe Altitude is a generic expression, used in various cases to denote an altitude below which it is unsafe to fly owing to presence of terrain or obstacles. The European drone regulation mentions that the UAS is maintained within 120 metres from the closest point of the surface of the earth during flight, except when overflying an obstacle. This study attempted to develop a minimum flight altitude database system. Based on domestic and international rules and regulations on setting the minimum flight altitude it is expected that it can be applied to the operation of aircraft and unmanned aerial system in UTM environments for specific area in Korea.

• Atmosphere
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• v.29 no.2
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• pp.219-226
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• 2019

Generally, the weather forecast system has been run using prescribed ocean condition. As it is widely known that coupling between atmosphere and ocean process produces consistent initial condition at all-time scales to improve forecast skill, there are many trials on the application of data assimilation of coupled model. In this study, we implemented a weakly coupled data assimilation (short for WCDA) system in global NWP model with low horizontal resolution for coupled forecast with uncoupled initialization, following WCDA system at the Met Office. The experiment is carried out for a typhoon evolution forecast in 2017. Air-sea exchange process provides SST cooling and gives a substantial impact on tendency of central pressure changes in the decaying phase of the typhoon, except the underestimated central pressure. Coupled data assimilation is a challenging new area, requiring further work, but it would offer the potential for improving air-sea feedback process on NWP timescales and finally contributing forecast accuracy.

• Journal of the Korean Solar Energy Society
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• v.39 no.4
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• pp.55-67
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• 2019

Recently, as the amount of particulate matter blowing from China increases, the domestic air environment is rapidly deteriorating. This pollution of the atmosphere greatly affects the light energy reaching the ground. Particularly, since the light enters the solar cell module in various forms, the amount of input energy of the solar power generation system may be changed depending on the ratio of direct beam irradiation and diffused horizontal irradiation. In this paper, we analyze how the ratio of direct beam component and diffused component on global horizontal irradiation varies with the atmospheric conditions. In addition, the reliability of the regression equation, designed to decompose the global horizontal irradiation into horizontal direct beam irradiation and diffused horizontal irradiation, was verified according to the level of air pollution. So, we derive the most suitable decomposition model for use in domestic climatic conditions in Korea by comparing the ratio of direct and diffuse component on the horizontal which is calculated with Perez model and Watanabe model using the meteorological weather data observed for 14 months. Finally, to reduce the error of the transposition result, we verified the reliability of the decomposition which depends on the atmospheric environment.

• Journal of Korean Society on Water Environment
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• v.35 no.2
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• pp.131-144
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• 2019

Climate Change affects the hydrological cycle in agricultural watersheds through rising air temperature and changing rainfall patterns. Agricultural watersheds in Korea are characterized by extensive paddy fields and intensive water use, a resource that is under stress from the changing climate. This study analyzed the effects of climate change on river flows for Geum Cheon and Eun-San Choen watershed using STREAM, a semi-distributed watershed model. In order to evaluate the performance and improve the reliability of the model, calibration and validation of the model was done for one flow observation point and three reservoir water storage ratio points. Climate change scenarios were based on RCP data provided by the Korea Meteorological Administration (KMA) and bias corrections were done using the Quantile Mapping method to minimize the uncertainties in the results produced by the climate model to the local scale. Because of water mass-balance, evapotranspiration tended to increase steadily with an increase in air temperature, while the increase in RCP 8.5 scenario resulted in higher RCP 4.5 scenario. The increase in evapotranspiration led to a decrease in the river flow, particularly the decrease in the surface runoff. In the paddy agricultural watershed, irrigation water demand is expected to increase despite an increase in rainfall owing to the high evapotranspiration rates occasioned by climate change.

• Journal of the Korea Institute of Military Science and Technology
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• v.25 no.2
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• pp.125-134
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• 2022

Recently, there are an increased the number of reports on the misuse or malicious use of an UAS. Thus, many researchers are studying on defense schemes for UAS by developing or improving C-UAS sensor technology. However, the wrong placement of sensors may lead to a defense failure since the proper placement of sensors is critical for UAS defense. In this study, a multi-object optimization model for C-UAS sensor placement in an air base is proposed. To address the issue, we define two objective functions: the intersection ratio of interested area and the minimum detection range and try to find the optimized placement of sensors that maximizes the two functions. C-UAS placement model is designed using a NSGA-II algorithm, and through experiments and analyses the possibility of its optimization is verified.

• Proceedings of the Korean Society of Computer Information Conference
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• 2024.01a
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• pp.379-382
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• 2024

본 논문에서는 위치기반 동역학(Position based dynamics, PBD)을 기반으로 하는 프레임워크를 활용하여 풍선 내 공기로 의한 표면의 회전과 변형을 효율적으로 표현할 수 있는 새로운 방법을 제안한다. 기존의 경우 볼륨 형태인 다면체 메쉬(Tetrahedral mesh)를 활용하여 표면 내부를 모델링 하거나 입자 기반의 유체 시뮬레이션을 통하여 공기역학을 계산해야 되지만, 각각의 동역학뿐만 아니라 상호작용까지 고려해야 되기 때문에 계산양이 커서 다양한 분야에서 활용하기 어렵다. 본 논문에서는 이 문제를 효율적으로 풀어내기 위해 공기의 움직임을 파악하기 위한 유체 시뮬레이션을 계산하지 않고도, 풍선 내 바람에 의한 표면 수축 및 확장을 PBD기반으로 풀어내고, 공기가 빠질 때 나타나는 표면의 회전을 효율적으로 계산할 수 있다. 본 논문에서 제안하는 방법은 정점(Vertex)의 개수가 많은 모델에서도 실시간 처리되는 결과를 보여 줄 수 있기 때문에 게임뿐만 아니라 실시간을 요구하는 물리기반 가상환경 구축에 활용될 수 있다.