• Journal of the Korean Society for Aviation and Aeronautics
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• v.16 no.4
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• pp.26-34
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• 2008

This article provides a comprehensive treatment of cracks in non-homogeneous structural materials such as functionally graded materials (FGMs). It is assumed that the material properties depend only on the coordinate perpendicular to the crack surfaces and vary continuously along the crack faces. By using laminated composite plate model to simulate the material non-homogeneity, we present an algorithm for solving the system based on Laplace transform and Fourier transform techniques. Unlike earlier studies that considered certain assumed property distributions and a single crack problem, the current investigation studies multiple crack problem in the FGMs with arbitrarily varying material properties. As a numerical illustration, transient thermal flow intensity factors for a metal-ceramic joint specimen with a functionally graded interlayer subjected to sudden heating on its boundary are presented. The results obtained demonstrate that the present model is an efficient tool in the fracture analysis of non-homogeneous material with properties varying in the thickness direction.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.1967-1977
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• 2014

In this paper, for the development of a safe and reliable DC home appliance suitable for DC home power supply system, we classified a number of inherent problems with help of the comparative analysis of existing AC and new DC home appliance. Several new technical problems of DC home appliances are mainly linked to the DC transient state. Among them, this paper concentrates on start-up inrush current problem, uni-polarity problem, and heavy DC load control problem. And to address these problems, we herein present an implementation of robust safety circuits for DC home appliances. Specifically, we investigate several multi-circuit countermeasures and select the best among them through comparative evaluation, based on theoretical, simulational, and experimental results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.10
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• pp.94-101
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• 2011

The proper installation of SPD and the evaluation of the SPD protection distance are basic steps for the effective protection measures of apparatus against surges within a structure. A novel method for installing SPD on the conventional distribution board without any modification was proposed and it's effectiveness was evaluated by experiments. Also, the transient overvoltage occurred across the power line from the SPD to the load was simulated with EMTP software to see how different the protection distances affecting the magnitude of the transient overvoltage. As evaluated, the effective protection method of apparatus against surges, coordinated SPD protection system is suggested as a proper measure to protect within the apartment.

• Journal of Power Electronics
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• v.14 no.6
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• pp.1263-1271
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• 2014

A novel hysteresis PWM control strategy for synchronous buck converter is proposed. The proposed control strategy is based on ampere-second balance of the modulate capacitor, which not only offers faster transient response to meet the challenges of the power supply requirements of fast dynamic load changes, but also provides better stability and solves the compensation problem of error amplifier in the conversional voltage PWM control. Finally, the steady-state and dynamic operation of the control method is analyzed and verified by simulation and experimental results.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.8
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• pp.482-492
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• 2002

This paper deals with overvoltage stresses in the field circuit of synchronous machine connected to HVDC terminal. A load rejection of the HVDC may cause generator in the station to become self-excited, resulting in a severe system overvoltage. This paper shows that violent field current oscillations can be produced by resonance between the machine inductance and the terminal capacitance. As most conventional excitation system do not allow reverses current, new topology of excitation system to allow reverse current is proposed. the proposed system can limit the rate of rise of terminal voltage during conditions of self excitation. Apart from these simulations, the nature(Magnitude and frequency) of the field transient state is explained mathematically. Finally, the EMTDC program is used for the simulation studies.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.136-139
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• 2005

On-line dynamic security assessment is becoming more and more important for the stable operation of power systems as load level increases. The necessity is getting apparent under Electricity Market environments due to more various operating conditions. Fast transient stability analysis tool is required for contingency selection. The TEF(Transient Energy Function) method is a good candidate for this purpose. The clustering of critical generators is crucial for the precise and fast calculation of energy margin. In this paper, we propose a new method for fast decision of mode of instability by using stability indices. Case study shows very promising results.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.167-175
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• 1997

The locus of a camshaft supported on camshaft bearings has been investigated using transient method. Forces applied to camshaft are composed of two components, one is transfer force between cam and tappet, the other is frictional force. These forces have been calculated using lumped mass model and EHL theory. ADI method has been used for numerical analysis of Reynolds equation, and 4th order Runge-Kutta method has been used for transient journal locus analysis. The effects of various load conditions are presented in the form of journal locus. As the result of analysis, it is found that camshaft bearings exist in the hydrodynamic lubrication condition.

• Tribology and Lubricants
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• v.13 no.4
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• pp.53-59
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• 1997

The camshaft locus at camshaft beating in a direct acting OHC valve train system has been investigated using the transient method. Forces applied to the camsfiaft are composed of two components, one is the transfer force between the cam and the tappet, the other is the frictional force. These forces have been calculated using the lumped mass model and the elastohydrodynamic lubrication theory. The alternating direction implicit method has been used for the numerical analysis of Reynolds equation, and 4th order Runge-Kutta method has been used for the transient journal locus analysis. The effects of various load conditions are presented in the form of journal locus. As a result of the analysis, it has been found that camshaft bearings were mainly in the hydrodynamic lubrication condition.

• Interaction and multiscale mechanics
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• v.5 no.4
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• pp.317-345
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• 2012

Cable-stayed bridges are often used in modern bridge engineering for connecting two geographical points of long distance. A special load case to cable-stayed bridges is earthquake, which can produce horizontal as well as vertical movements on the pylons of the bridge. These movements may be transient in nature, i.e., only resulting in the transient vibration of the bridge, but causing no damage consequences. In some extreme cases, they may cause permanent subsidence on one or more pylons of the bridge. In this paper, the effect of pylons' subsidence on the dynamic deformations of the bridge and on the cables' strength is thoroughly studied. Conclusions useful to the design of cable-stayed bridges will be drawn from the numerical study.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.12
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• pp.3069-3085
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• 1996

This paper shows an accurate charge-pump PLL model which considers the wave-form distortion in high speed operation of charge-pump PLL, the leakage current in loop filter, and a physical limit in charge-pump. With proposed model of charge-pump PLL, overload and stability are derived theoretically and the results are compared to the conventional model. Unlike the ideal charge-pump PLL that simplifies calculations, it is possible to analyze the transient-state and the steady-state at the same time with proposed accurate model. Thus, charge-pump over load, in the transient-state and the stead-state of charge-pump, is accuragely analyzed and the results are confirmed with simulation.