Seong-Man Choi

Analysis of Plume Infrared Signatures of S-Shaped Nozzle Configurations of Aerial Vehicle

The infrared susceptibility of the propulsion system of an aircraft is significantly affected by nozzle shapes and atmospheric conditions. To examine the effects of nozzle shapes and atmospheric conditions, various nozzle shapes were selected by considering a representative low-observable unmanned aerial vehicle and its propulsion system. Then, using the density-based Navier–Stokes–Fourier computational-fluid-dynamics code, the thermal flowfield and the distribution of chemical species within a plume, which are essential for the analysis of infrared signatures, were calculated. From the analysis of plume infrared signatures for noncircular nozzles, it was found that infrared signature levels were reduced significantly in the axial direction. However, relatively higher signature levels were observed on the left and right sides and below the nozzle due to increase in the aspect ratio of the nozzle outlet as well as curvature, which led to a wider distribution of the plumes along a downward slope. Further, t...

Integrated Management Data Warehouse Development Process of Research Expenses in Enterprise Environment

The existing management job of research expenses has been divided into three parts： budget planning, budget draw-up, and exact settlement of budget. However, it caused some problems. Under this current circumstance it is required to obtain research expenses steadily, to operate efficiently and to use them clearly to solve such problems. As a result of a study on data warehouse development process of existing system integration company (Inmon, IBM) to reflect current trend described above, data warehouse development process of Inmon uses systematic and gradual access as a classical development cycle method. It causes overlap and feedback to the previous step in the process of each step Is requested. And another problem that it is difficult to toil what function refers and corrects data because functions and data are separated during performing development process at data warehouse development process of IBM is caused. Integrated management data warehouse development process of research expenses in the enterprise environment which applies UML at planning and analysis step, design step and implement and test step is suggested in this paper. Information retrieval agent uses existing budget plan DB, budget draw-up DB and budget settlement DB to find out information that a user wants to know. Information retrieval agent collects and saves information at integration database and information integration agent extracts, transports, transforms and loads the data. Information integration agent reduces a user`s efforts to access to a number of information sources and check each of them. It also screens out data that a user may not need. As a result, integrated management data warehouse development process of research expenses in the enterprise environment reflects a user`s requirements as much as possible and provides various types of information to make a decision which is needed to establish the policy of research expense management. It helps an end user approach his/her desired analysis information quickly and get various data from the comprehensive viewpoint rather than the fragmentary viewpoint. Furthermore, as it integrated three systems into one, it is possible to share data, to integrate the system, to reduce operating expenses and to simplify supporting environment for the decision making.

A cooperation model using reinforcement learning for multi-agent

In multi-agent systems, the common goals of each agent are established and the problems are solved through cooperation and control among agents. Because each agent performs parallel processes in a multi-agent system, this approach can be easily applied to problems requiring parallel processing. The parallel processing prevents system performance degradation due to local error operation in the system. It also can reduce the solution time when the problem is divided into several sub-problems. In this case, each agent is designed independently providing a relatively simple programming model for solution of the problem. Further, the system can be easily expanded by adding new function agents. In the study of multi-agent systems, the main research topic is the coordination and cooperation among agents.

COMPUTATIONAL INVESTIGATION OF NOZZLE FLOWFIELD IN A MICRO TURBOJET ENGINE AND ITS SCALING CHARACTERISTICS

Thermal flowfield of a micro turbojet engine was computationally investigated for exhaust nozzles with different aspect ratio and curvature. Special attention was paid to maximum and average temperature of the nozzle surface and the exhaust nozzle plume. The IR signatures of the micro turbojet engine nozzle were then calculated through the narrow-band model based on thermal flowfield data obtained through CFD analysis. Finally, in order to check the similarity of thermal flowfields and IR signature of the sub-scale micro turbojet engine model and the full-scale UCAV propulsion system, several non-dimensional parameters associated with temperature and optical property of plume were introduced. It was shown that, in spite of some differences in actual values of non-dimensional parameters, the scaling characteristics on spectral feature of IR signature and effects of aspect ratio and curvature of nozzle configuration remain similar in sub-scale and full-scale cases.

Investigation of IR Survivability of Unmanned Combat Aerial Vehicle against Surface-to-Air Missiles

As the survivability of an aircraft in the battlefield becomes a critical issue, there is a growing need to improve the survivability of the aircraft. In this study, the survivability of an UCAV associated with plume IR signature was investigated. In order to analyze the survivability of the aircraft, the lock-on range and the lethal envelope, defined as the IR detection distance of the aircraft and the range of shooting down by the missile, respectively, were first introduced. Further, a method to calculate the lethal envelope for the scenario of surface-to-air missiles including the vertical plane was developed. The study confirmed that the red zone of an UCAV shows a substantial difference in the zone size as well as the characteristics in the upward and downward directions.

Experimental Study of a Micro Turbo Jet Engine Performance and IR Signal with Nozzle Configuration

Micro turbojet engine test and infrared signal measurement were conducted to understand the characteristics of the engine performance and infrared signal with the variants of the exhaust nozzle configuration. A cone type nozzle and five rectangle type nozzles which has aspect ratio from one to five were used for the experimental work. The results show that there are not much difference between cone and rectangle nozzles of the thrust and specific fuel consumption. However infrared signal from exhaust gas become smaller as increasing aspect ratio.

Measurement and Validation of Infrared Signature from Exhaust Plume of a Micro-Turbo Engine

A development of accurate measurement system of infrared signature is considered to contribute to the development of low observable technology and the spectroscopic analysis of electromagnetic radiation. The application of a spectroradiometer (SR) allows a measurement of detailed infrared signature from exhaust plume due to its own heat source. A establishment of the measurement system using a micro-turbo engine is intended to simulate a modelling the plume of aircraft. The engine was installed on the test stand to measure the engine performance. The IR signature was measured by placing the SR perpendicular to the axis line of the exhaust plume. The reference data from the blackbody were also measured to calibrate the raw data, and the infrared signature of the background was also measured for a comparison with that of the plume. The calibrated spectral radiance was obtained through the data reduction process and the results were analyzed in specific bands. The experiments revealed that the measurement system established here was very good enough to study a further comprehensive analysis.

Conceptual Study of an Exhaust Nozzle of an Afterburning Turbofan Engine

ABSTRACT This paper presents a preliminary study of a convergent diver gent nozzle in an afterburning turbofan engine of a supersonic aircraft engine. In order to design a convergent divergent nozzle, cycle model of a low bypass afterburning turbofan engine of which thrust class is 29,000 lbf at a sea level static condition is established. The cycle analysis at th e design point is conducted by Gasturb 12 software and one dimensional gas properties at a downstream direction of the turbine are obtained. The dimension and configuration of an model turbofan engine are derived from take-off operation with wet reheat condition. The off-design cycle calculation is conducted at the all flight envelope on the maximum flight Mach number of 2.0 and maximum flight altitu de of 15,000 m. 초 록 초음속 항공기의 추진기관으로 이용되는 후기연소기 장착 터보팬 엔진의 축소-확대 노즐에 대한 예비연구를 수행하였다. 이를 위하여 지상정지 표준 대기에서 29,000 lbf 급의 추력을 발생시키는 저 바이패스비를 가진 후기 연소기 장착 터보팬 엔진에 대한 사이클 모델을 설정하였다 . 설정된 모델 엔진을 이용하여 Gasturb 12 소프트웨어로 설계점에 대한 성능해석을 수행하여 터빈 후방에서의 일차원 유동특성을 얻을 수 있었다. 항공기 이륙시의 최대추력 조건으로부터 바이패스 덕트와 코어엔진에서 흐르는 가스유동으로부터 엔진의 크기 및 형상에 대한 기본제원을 도출하였다. 탈 설계점 성능해석은 최대 비행 마하수 2.0, 최고 비행고도 15,000 m로 운용되는 항공기의 다양한 운용조건에 대하여 수행하였다. Key Words: Supersonic Aircraft(초음속 항공기), Afterburning Turbofan Engine(후기연소기 장착 터보팬 엔진), Convergent Divergent Nozzle(축소확대 노즐), Cycle Analysis(싸이클해석)Received 21 December 2013 / Revised 6 May 2014 / Accepted 14 Ma y 2014

Experimental analysis on the characteristics of enthalpy probe immersed in arc plasma flow

Enthalpy probe with the inner and outer diameters of 1.5 mm and 4.8 mm, respectively, is designed and used to measure the temperatures and velocities along the centerline of Ar arc plasma flow until the probe was destroyed. For this purpose, Ar arc plasma flow is generated by non-transferred type DC arc heater with the power level of 17 kW. From this experiment, it is shown that the designed enthalpy probe can measure the temperature and velocity of arc plasma flow up to 12,000 K and 600 m/s, respectively, without destroy of probe tip. In this extreme case, the arc plasma flow is calculated to transfer the heat flux of to the probe based on the heat and thermal boundary equations near the forward stagnation point of a body immersed in arc plasma flow. Consequently, the designed enthalpy probe can measure the wide ranges of plasma temperatures, velocities and concentrations simultaneously, which are generated by various types of arc heaters within the heat flux ranges of on the probe tip.

Process development methodology for u-integrated management system

Existing research expenses management task consists of budget planning, budget draw-up, and exact settlement of budget. Therefore integrated management is needed keenly for certain security, efficient operation and clear execution of research expenses. To reflect these needs, Research Expenses Integrated Management(REIM) has been offered for the application used on mobile by reusing an business application module has been developed in REIM development process. Mobile collaboration component which supports a specialized collaboration process to be adapted for the peculiarities of a mobile machine also has been developed. As a result, it can offer various supportive information for decision making for the establishment of research management policy by reflecting users requirement in real-time. It can also provide accuracy and prevention of errors to each operation since it can grasp the process of each operation without time and space hindrance through mobile collaboration.