• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.110-117
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• 2003

The operational characteristics of the landing gear retraction/extension depend on the complexity of design variables operational/environmental conditions. In order to meet the requirements of minimum stow area and performance, the integration of the landing gear system requires operational kinematic and dynamic analysis considering an effect of its related system. This study investigates operational dynamic behaviors of the T-50 landing gear system using ADAMS. Taking into account for various operational/environmental conditions, an analysis of dynamic behavior on the landing gear operational characteristics is performed with experience derived from a wide range of proprietary designs. Analytical results are presented for discussing the effects of temperature, aerodynamic and maneuver load on normal/emergency operation of the landing gears and doors. This analysis leads us to the conclusion that the proposed program is shown to be a better quantitative one that apply to a new development and troubleshooting of the landing gear system.

• Journal of the Korean Electrochemical Society
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• v.7 no.2
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• pp.69-79
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• 2004

To correctly simulate performance characteristics of fuel cells with a modeling method, various physical and chemical phenomena must be considered in fuel cells. In this study, performance characteristics of planar solid oxide fuel cells were simulated by a commercial CFD code, CFD-ACE+. Through simultaneous considerations for mass transfer, heat transfer and charge movement according to electrochemical reactions in the 3-dimensional planar SOFC unit stack, we could successfully predict performance characteristics of solid oxide fuel cells under operation for structural and progress variables. In other words, we solved mass fraction distribution of reactants and products for diffusion and movement, and investigated qualitative and quantitative analysis for performance characteristics in the SOFC unit stack through internal temperature distribution and polarization curve for electrical characteristics. Through this study, we could effectively predict performance characteristics with variables in the unit stack of planar SOFCs and present systematic approach for SOFCs under operation by computer simulation.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.731-736
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• 2011

A pneumatic driving solenoid valve operates pneumatic control devices by opening/closing operating flow passage when the command is given by control system for the liquid-propellant feeding system of space launch vehicle. The simulation model of pneumatic driving solenoid valve is designed with AMESim to verify the designs and evaluate the dynamic characteristics and pneumatic behaviors of valve. To validate a valve simulation model, the simulation results of their operating durations of valve by AMESim analysis are compared with the results of experiments. In addition, the results of internal flow simulation with FLUENT are utilized to improve the accuracy of valve-modeling. Using the model, we analyze performance of valve; opening/closing pressure, operating time on various design factors; shape of control valve seat, drainage seat, rate of sealing diameter, volume of control cavity. This study will serve as one of reference guides to enhance the developmental efficiency of ventilation-relief valves with the various operating conditions, which shall be used in Korea Space Launch Vehicle-II.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.5
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• pp.214-221
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• 2015

In this paper, we present robust estimation and detection algorithms for discrete-time switched linear systems whose output measurements are corrupted by noises. First, a mode estimation algorithm is proposed based on the minimum distance criterion. Then, state variables are also observed under the active mode estimate. Second, a detection algorithm is constructed to detect the mode switching of the switched system. With the boundedness of measurement noise, the proposed estimation algorithm returns the exact active mode and approximate state information of the switched system. In addition, the detection algorithm can detect the switching time within a pre-determined time interval after the actual switching occurred.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.971-980
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• 1990

본 연구에서는 실험적으로 2상 밀폐 직사각형 열사이폰 루프에 대하여 안정성 에 주된 영향을 줄수 있는 변수들, 즉 루프 경사각도, 작동유체의 유동현상을 관찰하 고 작동유체의 온도변동과 류프의 전열성능을 측정하여 열사이폰이 안정하게 작동하는 범위를 종합적으로 조사해 보았다.

• Aerospace Engineering and Technology
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• v.11 no.2
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• pp.109-116
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• 2012

A vent-relief valve performs as a safety-valve assembly for liquid propellant feeding system of space launch vehicle, which relives pressurant propellant tanks during the filling and the flight. At vent mode, valve is opened and closed by driving pneumatic pressure, and at relief mode, valve is automatically operated to set relief pressure. In this study, we have analyzed a basic layout of vent-relief valve which is designed using foreign LVs(Saturn) to satisfy requirements of Korean Space Launch Vehicle. The simulation model of vent-relief valve is designed by using the AMESim code to verify design parameters and evaluate pneumatic behaviors of valve. In this study, we performed dynamic characteristic simulations on design parameters. And we could predict opening/closing time and pressures, operating performances on design parameters. Using this results, we could suggest detail design and boundary conditions of design.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1133-1140
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• 2013

A computer model is a useful tool that provides solution via physical modeling instead of expensive testing. In reality, however, it often does not agree with the experimental data owing to simplifying assumption and unknown or uncertain input parameters. In this study, a Bayesian approach is proposed to calibrate the computer model in a probabilistic manner using the measured data. The elasto-plastic analysis of a pyrotechnically actuated device (PAD) is employed to demonstrate this approach, which is a component that delivers high power in remote environments by the combustion of a self-contained energy source. A simple mathematical model that quickly evaluates the performance is developed. Unknown input parameters are calibrated conditional on the experimental data using the Markov Chain Monte Carlo algorithm, which is a modern computational statistics method. Finally, the results are applied to determine the reliability of the PAD.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1036-1042
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• 2012

This paper describes an analysis on exergy efficiency of R744 OTEC power system to optimize the design for the operating parameters of this system. The operating parameters considered in this study include subcooling and superheating degree, evaporation and condensation temperature, and turbine and pump efficiency, respectively. The main results are summarized as follows : As the evaporation temperature, superheating degree, and turbine and pump efficiency of R744 OTEC power system increases, the exergy efficiency of this system increases, respectively. But condensation temperature and subcooling degree of R744 OTEC power system increases, the exergy efficiency of this system decreases, respectively. The effect of evaporation temperature and pump efficiency on R744 OTEC power system is the largest and the lowest among operation parameters, respectively. Therefore, the refrigerant temperature in the evaporator must be closely to the surface seawater temperature to enhance the exergy efficiency of R744 OTEC power system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.4
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• pp.1548-1554
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• 2013

This paper presents the analysis on performance characteristics of R744-R410A cascade refrigeration system to offer the basic design data for the operating parameters of this system. The performance of cascade refrigeration system is analyzed by using EES program. The operating parameters include compressor efficiency, and condensing and evaporating temperature in R410A high- and R744 low-temperature cycle, respectively. The COP of this system increases with the decrease of condensing temperature, and increases with the increasing evaporating temperature. And the COP of this system increases with the compression efficiency. Therefore, it can be seen that the compression efficiency, and evaporating and condensing temperature of R744-R410A cascade refrigeration system have an effect on the COP of this system. Also, it can be known that the cascade evaporation temperature with the highest efficiency in each parameter is present. Thus, it is an important to design R744-R410A cascade refrigeration system by considering these parameters.

• The Journal of the Korea Contents Association
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• v.15 no.12
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• pp.185-192
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• 2015

This study analyzed the spatial interrelation between living wages and economic variables and how they operate based on systems thinking theory to understand what value living wages have as policy instruments and why they are necessary. Results from this study can be summed as follows. First, the relationship between living wages and economic variables shows close interaction at a considerable level. In particular, mutual feedback which connects to laborers' standards of living, consumption, business, and economy was operating closely. Second, largely three positive (+) feedback loops were operating in the feedback structure of living wages and economic variables. This can be interpreted to mean that positive economic variables which are associated with living wages have the possibility of growth. Also, it can mean that the minimum wage system did not fully fulfill its role. Through these study results, it can be learned that living wages have sufficient value as a policy means and that it is advisable to allow living wages to exceed simple application levels in the public sector to expand into the private sector, to bring positive change to the economic system.