• Journal of Mechanical Science and Technology
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• 제18권11호
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• pp.2021-2031
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• 2004

A new nondimensional method for predicting the windmilling performance of centrifugal -flow turbojet engines in flight has been developed. The method incorporates loss correlations to estimate the performance of major engine components. Given basic engine geometry, flight Mach number, and ambient conditions, this method predicts transient and steady-state windmilling performance. Thus, this method can be used during the preliminary design stage when detailed hardware geometry and component performance data are not yet available. A nondimensional time parameter is newly defined, and using this parameter, the transient performance of different types of turbojets (e.g. centrifugal vs. axial) is compared. In addition, the predictions' sensitivity to loss correlations, slip factors, and inlet ambient temperatures are analyzed.

• 한국자동차공학회논문집
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• 제10권4호
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• pp.122-128
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• 2002

In this paper dynamic responses of an engine, which is supported by hydraulic mount, to throttle tip-in/Tip out are analyzed. Because the hydraulic mounts have non-linearity that the characteristics of stiffness and damping vary with frequencies, it is difficult to analyze the dynamic behavior of an engine using general integral algorithms. Convolution integral and relationship between unit impulse response functions and frequency response functions are therefore used to simulate the transient behaviors of an engine indirectly. In time domain, impulse response functions are calculated by two-side discrete inverse courier transform of frequency response function achieved by laplace transform of equations of motion. Considering the fact that the shapes of behavior of an engine simulated by the proposed method are in good agreement with test results, it is confirmed that the proposed method is very effective for the analysis of transient response to throttle tip-in/out of an engine with hydraulic mounts.

• 한국추진공학회지
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• 제10권4호
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• pp.19-25
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• 2006

STS 304 발열선과 $Zr-KCIO_4$ 기폭화약을 사용한 전기식 착화기에 대한 열전이 특성을 시험하고 Fitted Wire Model로 분석한 결과, 약 $300^{\circ}C$ 부근에서 기폭화약과 관련된 열전이 특성 파라미터가 급격하게 변화되었다. 이 현상은 기폭화약에 사용된 $KCIO_4$의 상변화로 인한 흡열반응에 의해 발생된 것으로 판단된다.

• KIEE International Transactions on Power Engineering
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• 제5A권4호
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• pp.366-370
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• 2005

To meet increasing power demand, 500 kV power systems are under consideration in the regions of some Middle Asian countries. As the power system voltage becomes higher, the cost for the power system insulation increases significantly. 500 kV transmission systems will become the basis of a region's power system and they require much higher system reliability. Consequently, by the methods of limiting overvoltages effectively, a reasonable insulation design and coordination must be accomplished. In particular, the Substations must be constructed to be of outdoor type. In order to determine the various factors for the insulation design, the EMTP (Electro-magnetic transient program) is used for the magnification of transient phenomena of the 500 kV systems in the planned network. In this paper, we will explain the calculation results of lightning overvoltages by the EMTP for lightning protection design for the 500 kV substations. To obtain reliable results, the multi-story tower model and EMTP/TACS model are introduced for the simulation of dynamic arc characteristics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.855-858
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• 2001

The stress induced leakage currents of thin silicon oxides is investigated in the VLSI implementation of a self learning neural network integrated circuits using a linearity synapse transistor. The channel current for the thickness dependence of stress current, transient current, and stress induced leakage currents has been measured in oxides with thicknesses between 41 ${\AA}$, 86${\AA}$, which have the channel width ${\times}$ length 10 ${\times}$1${\mu}$m, 10 ${\times}$0.3${\mu}$m respectively. The stress induced leakage currents will affect data retention in synapse transistors and the stress current, transient current is used to estimate to fundamental limitations on oxide thicknesses. The synapse transistor made by thin silicon oxides has represented the neural states and the manipulation which gaves unipolar weights. The weight value of synapse transistor was caused by the bias conditions. Excitatory state and inhitory state according to weighted values affected the channel current. The stress induced leakage currents affected excitatory state and inhitory state.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.906-909
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• 2005

In this study, the dynamic flying characteristics of the worn head sliders are investigated theoretically due to the change in head geometry caused by head and disk contact. The film shapes can be approximated as taper- truncated cycloidal-flat film. Two-dimensional time dependent modified Reynolds equation included molecular slip effect are formulated with neglected the roughness effect. The motion of head slider was assumed to have two degree of freedom in this work. Finite difference approximation with Newton Raphson iterative technique and the fourth order Runge-Kutta method were implemented to obtain the transient response of the slider head with various change in head geometry numerically and compared with the transient response of the IBM3380 type head slider. The simulation results show the film shape has affects significantly on the static and dynamic characteristic of slider head in magnetic storage systems.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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• pp.6-10
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• 2003

Accurate description of starting transient history allows and justifies the use of small margin of safety for the engine parts, resulting in high motor mass ratio in addition to satisfying the control and guidance requirements of the vehicle. Studies have been carried out for the prediction and reduction of ignition peak and pressure-rise rate during the starting transient of solid rocket motors. Numerical studies have been carried out using a two dimensional Navier-Stokes solver. It has been inferred through the parametric studies that, in the case of solid rocket motors with uniform port, high ignition peak is observed at high spread rate and low pressure-rise rate. In the case of the port with sudden expansion configuration, high ignition peak is observed at relatively high average spread rate and high-pressure rise rate. These studies are expected to aid the designer in reducing the ignition peak by altering the propellant properties or igniter characteristics without sacrificing the motor performance.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 추계학술대회 논문집 학회본부
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• pp.245-249
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• 1989

From the careful analysis of the transformed dq system equations of a PWM Voltage Source Converter ( PWM - VSC ), a novel voltage control is proposed which is based on the derivative of in-phase current component of line currents and the relation between dc-link voltage and in-phase current component. A simple logical algorithm to implement the proposed scheme is also presented at transient state. The sinusoidal PWM is adopted at steady state. The simulation results show good transient characteristics.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 춘계학술대회 논문집 전력기술부문
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• pp.245-247
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• 2001

This paper presents a series of simulation results of transient stability on SCOPF operated power system whose transmission capabilities are limited by voltage stability. Three steps of voltage security guidelines, 5[%], 7[%], 10[%] are introduced to increase power transfer from generation centers to load center and observed the effects of voltage guidelines to transient stability for three kinds of load level(peak, medium, off-peak). As a result, dynamic characteristics weren't affected by the voltage security limits in model system, but became worse for the off-peak level than peak case, and sustain oscillations are observed for the all load level. This gives us some intitutions for the development and applications of security limits to use SCOPF program in open electric market.

• 한국지능시스템학회논문지
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• 제5권4호
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• pp.87-100
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• 1995

In order to control systems which contain nonlinearities of uncertainties, control strategies must deal with the effects of them. Since most of control methods based on system mathematical models have been mainly developed focused on stability robustness against nonlinearities or uncertainties under the assumption that controlled systems are linear time invariant, they have certain amount of limitations to smartly improve the transient responses of systems disturbed by nonlinearities or uncertainties. In this paper, a nonlinear fuzzy PID control method is suggested which can stably improve the transient responses of systems disturbed by nonlinearities, as well as systems whose mathematical characteristics are not perfectly known. Although the derivation process is based on the design process similar to general fuzzy logic controller, resultant control law has analytical forms with time varying PID gains rather than linguistic forms, so that implementation using common-used versatile microprocessors cna be achieved easily and effectively in real-time control aspect.