• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3203-3208
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• 2007

The performance study shows the result using two different methods which are used to control missile or aircraft. One is the Thrust Vector Control(TVC) method for the aviation of next generation and the other is the present effective Shroud Jet-vane System(SJVS) method for the satellite effector development. The research was done through the performance estimation using the numerical simulation analysis, the modelling, the performance measuring using the model, the investigation of the flow visualization and aerodynamic performance with the enforced power to the vane and the result comparison.

• Journal of Korean Association for Spatial Structures
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• v.15 no.3
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• pp.95-102
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• 2015

Numerical model on precast prestressed concrete (PC) hollowcore slabs using 11.3 mm diameter 7-wire stand was developed based on finite element analysis. In order to validate the modelling, previous experiment results with respect to prestressed solid concrete slabs were used and compared throughout the course of fire exposure. In addition to, the fire performance of hollowcore slabs with different aggregate types, moisture contents and compressive strength of concrete was investigated. As a result, it can be seen that the type of aggregates and moisture contents used in hollowcore slabs can affect the fire performance as well as temperature developments.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.723-728
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• 2007

In order to evaluate the performance of carbon dioxide cycle with a sub-cooling loop. a simulation system was developed to predict the steady state of $CO_2$ trans-critical cycle. Mathematical models are derived to describe the relationships between the system's coefficient of performance and other operating parameters The mathematical models are based entirely on the basic mass and energy conservation law and thermodynamic and transport properties of carbon dioxide A parametric study has been conducted in order to investigate the effect of sub-cooling loop and various operating conditions on the cycle performance. An optimal mass fraction of a refrigerant flowing through sub-cooling cycle existed for the given evaporating temperature, high pressure and air inlet temperature through gas cooler.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.833-836
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• 1999

In this paper, the communication performance and its characteristics of the polar Low Earth Orbit(LEO) mobile satellite have been described in terms of the generalized performance parameters via geometric modeling and analysis. Especially, the general formula related to the parameters such as the number of orbits(M) and the number of satellites per orbit(N) were derived in the LEO satellite system for voice service, and then we applied the general result to IRIDIUM system(M＝6, N＝11) that would be scheduled to commercialize soon. The offered traffic of Inter Satellite Link(ISL), ISL link blocking probability as well as both new call blocking probability and the probability of forced termination for the on going call are calculated as the result of performance analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.1
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• pp.84-90
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• 2004

In order to evaluate the performance of carbon dioxide cycle, a simulation model was developed to predict the steady state performance of $CO_2$ transcritical cycle. The expansion process is treated as an isenthalpic throttling process or isentropic expansion process. The mathematical model is based entirely on the basic energy conservation law and thermodynamic and transport properties of $CO_2$. A Parametric study has been conducted in order to investigate the effect of isentropic efficiency of expansion turbine and various operating conditions on the cycle performance. An optimal heat rejection pressure existed for the given evaporating temperature and outlet temperature of gas cooler.

• Communications for Statistical Applications and Methods
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• v.18 no.2
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• pp.201-211
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• 2011

In many cases, populations in the real world are composed of different subpopulations. Furthermore, in addition to the heterogeneity in the lifetimes of items, there also could be the heterogeneity in the efficiency or performance of items. In this case, the reliability measures should be defined in a different way. In this article, we consider the mixture of stochastically ordered subpopulations. Efficiency based reliability measures are defined when the performance of items in the subpopulations has different levels. Discrete and continuous mixing models are studied. The concept of the association between the lifetime and the performance of items in subpopulations is defined. It is shown that the consideration of efficiency can change the shape of the mixture failure rate dramatically especially when the lifetime and the performance of items in subpopulations are negatively associated. Furthermore, the modelling method proposed in this paper is applied to the case when the stress levels of the operating environment of items are different.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.437-442
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• 1997

To determine the optimum pressurizer water level during normal operation for Kori unit 1, performance and safety analysis are peformed. The methodology is developed by evaluating "decrease in secondary heat removal" events such as Loss of Normal Feedwater accident. To demonstrate optimum pressurizer level setpoint, RETRAN-03 code is used for performance analysis. Analysis results of RETRAN following reactor trip are compared with the actual plant data to justify RETRAN code modelling, The results of performance and safety analyses show that the newly established level setpoints not only improve the performance of pressurizer during transient including reactor trip but also meet the design bases of the pressurizer volume and pressure. pressure.

• Journal of the Korea Society for Simulation
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• v.12 no.4
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• pp.103-111
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• 2003

A distributed sewer cluster system is a cost-effective system to provide a service application for clients with reliable, scalable, available, and fault-tolerant features. In order to provide high quality services, it is necessary to evaluate service performances, tune the server system, and analyze performances. In this paper, we propose a simulator to generate workloads based on statistic configuration according to estimated application traffics, apply workload scheduling algorithms, and evaluate the simulation results. We introduce the simulator design modelling and architecture. By using flexible parameters, the simulator is able to generate various patterns of workloads with different statistics, and configure system environments such as the number of server nodes, system resources considered, and their capacities. With this simulator, we introduce two scenarios: one is to find appropriate thresholds for the best performance of cluster system, and the other is to find the suitable scheduling algorithm for workload characteristics of service applications.

• Journal of the Korean Institute of Navigation
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• v.4 no.1
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• pp.19-30
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• 1980

The usual procedure for the optimal design of ship's steering system is to minimize a chosen quadratic performance index, which isdetermined from the view point of economic run. However, the optimal control synthesized in such a straightforward fashion is unsatisfactory because ship's parameters differ from their nominal values due to uncertainties and errors in measurement and/or simplifications in mathematical modelling, and/or the variation of the ship's loading condition. In an attempt to resolve this difficulty, this paper presents a method for designing a low sensitive optimal steering system in a way as to minimize not only given performance index but also the sensitivity of the performance index and trajectory sensitivity. It is also shown that the optimal control so obtained will result in a system whose performance index and transient response are low sensitive to small varation in ship's time constant.

• Proceedings of the Korea Society for Simulation Conference
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• 2003.11a
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• pp.27-34
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• 2003

A distributed server cluster system is a cost-effective system to provide a service application for clients with reliable, scalable, available, and fault-tolerant features. In order to provide high quality services, it is necessary to evaluate service performances, tune the server system, and analyze performances. In this paper, we propose a simulator to generate workloads based on statistic configuration according to estimated application traffics, apply workload scheduling algorithms, and evaluate the simulation results. We introduce the simulator design modelling and architecture. By using flexible parameters, the simulator is able to generate various patterns of workloads with different statistics, and configure system environments such as the number of server nodes, system resources considered, and their capacities. With this simulator, we introduce two scenarios: one is to find appropriate thresholds for the best performance of cluster system, and the other is to find the suitable scheduling algorithm for workload characteristics of service applications.