• 한국재료학회지
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• 제12권2호
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• pp.103-111
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• 2002

The thermally insulated underground pipelines have been used for district heating system. The sensor wire embedded in the insulation was used for monitoring the insulating resistance between the sensor wire and the pipe. The resistance measurement system detects corrosion of steel pipe under insulation. The corrosion and stress corrosion cracking(SCC) characteristics of sensor wire in synthetic ground water were investigated using the electrochemical methods and constant load SCC tests. The polarization tests were used to study the electrochemical behavior of sensor wire. The sensor wire was passivated at temperatures ranging from 25 to $95^{\circ}C$. However, the applied sensing current larger than passive current resulted in breakdown of passive film. The constant load SCC tests were performed to investigate the effects of applied current and load on the fracture behavior. Stress-corrosion cracks initiated at pits that were produced by sensing current. The growth of the pit involves a tunnelling mechanism, which leads to ductile fracture.

• 한국정밀공학회지
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• 제20권2호
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• pp.136-145
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• 2003

The integrity of stiffened panels with stringers in airplane structure is generally enhanced by investigating the fatigue crack propagation behavior in detail and providing the technical methodology to deal with the propagating crack. This paper attempts to clarify the effect of load-ratio on the fatigue crack propagation rate and the fatigue life for the thin aluminum 2024-T3. Both the variable and the constant fatigue loading conditions are considered for the fatigue crack propagation behavior in stiffened panels with stringers.

• 대한기계학회논문집
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• 제18권2호
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• pp.271-277
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• 1994

The fatigue crack opening behavior is analyzed using finite element method. Because extremely fine mesh subdivision is required when using constant stress constant strain triangular element, this study uses conventional two dimensional eight node isoparametric elements. Since plasitc zone size is similar to crack propagating length per each load cycle because of relatively large element size, a new analysis model that a crack propagates every two load cycle is suggested. the opening load and crack opening displacement can be obtained accurately by this method.

• Structural Engineering and Mechanics
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• 제54권4호
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• pp.649-664
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• 2015

In this study, the authors present an analytical approach to find the axisymmetric buckling load of two joined isotropic conical shells under axial compression. The problem of two joined conical shells may be considered as the generalized form of joined cylindrical and conical shells with constant or stepped thicknesses. Thickness of each cone is constant; however it may be different from the thickness of the other cone. The boundary conditions are assumed to be simply supported with rigid rings. The governing equations for the conical shells are obtained and solved with an analytical approach. A simple closed-form expression is obtained for the buckling load of two joined truncated conical shells. Results are compared and validated with the numerical results of finite element method. The variation of buckling load with changes in the thickness and semi-vertex angles of the two cones is studied. Finally, application of the results in practical design and range of engineering validity are investigated.

• Journal of Electrical Engineering and Technology
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• 제12권3호
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• pp.1235-1244
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• 2017

This paper proposes a fuzzy logic controlled new topology of high voltage gain zero voltage switching (ZVS) asymmetrical PWM full-bridge DC-DC boost converter for constant load and high power applications. The APWM full-bridge stage provides high voltage gain and soft-switching characteristics increase the efficiency and reduce the switching losses. Fuzzy logic controller (FLC) improves the performance and dynamic characteristics of the proposed converter. A comparison with a classical proportional-integral (PI) controller demonstrates the high performances of the proposed technique in terms of effective output voltage regulation under different operating conditions. Simulation is done by integrating two different simulation platforms $PSIM^{(R)}$ and $Matlab^{(R)}/Simulink^{(R)}$ by using SimCoupler tool of $PSIM^{(R)}$. Experimental results using 120W load have been provided to validate the results.

• 한국산학기술학회논문지
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• 제5권4호
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• pp.286-291
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• 2004

실무 현장에서 피로 파괴가 잘 일어나고 있는 상황이다. 그런데 그 하중도 불규칙적으로 일어나고 있어 예측이 불가능하여 언제 파괴가 일어나는지를 잘 알 수가 없는 상황이다. 본 연구에서는 그러한 불규칙적인 피로 하중을 시뮬레이션 하여 그 재료의 안정성과 수명 관계를 Ansys workbench 프로그램을 이용하여 이론적으로 해석하여 보았다. 이러한 결과들을 실제 구조물에서 응용하면 그 파손 방지 및 내구성을 예측하는데 활용이 크다고 본다.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2004년도 춘계학술대회
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• pp.100-102
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• 2004

실무 현장에서 피로 파괴가 잘 일어나고 있는 상황이다. 그런데 그 하중도 불규칙적으로 일어나고 있어 예측이 불가능하여 언제 파괴가 일어나는지를 잘 알 수가 없는 상황이다. 본 연구에서는 그러한 불규칙적인 피로 하중을 시뮬레이션하여 그 재료의 안정성과 수명 관계를 Ansys workbench 프로그램을 이용하여 이론적으로 해석하여 보았다. 이러한 결과들을 실제 구조물에서 응용하면 그 파손 방지 및 내구성을 예측하는데 활용이 크다고 본다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.176-179
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• 2005

Spray casting of hypereutectic Al-Si based alloy has been reported to provide distinct advantages over ingot metallurgy (IM) or rapid solidification/powder metallurgy (RS/PM) process in terms of microstructure refinement. Hypereutectic Al-Si based alloys have been regarded attractive for automotive and aerospace application, due to high specific strength, good wear resistance, low coefficient of thermal expansion, high thermal stability, and good creep resistance. In this study, hypereutectic Al-25Si-2.0Cu-1.0Mg alloy was prepared by OSPREY spray casting process. High temperature deformation behavior of the hypereutectic Al-Si based alloy has been investigated by applying the internal variable theory proposed by Chang et al. The change of strain rate sensitivity and Creep transition were analyzed by using the load relaxation test and constant creep test.

• 대한전기학회논문지
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• 제35권5호
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• pp.193-198
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• 1986

In this paper, 1-168 hours ahead load prediction algorithm is developed for power system economic weekly operation. Total load is composed of three components, which are base load, week load and weather-sensitive load. Base load and week load are predicted by moving average and exponential smoothing method, respectively. The days of moving average and smoothing constant are optimally determined. Weather-sensitive load is modeled by linear form. The paramiters of weather load model are estimated by exponentially weighted recursive least square method. The load prediction of special day is very tedious, difficult and remains many problems which should be improved. Test results are given for the day of different types using the actual load data of KEPCO.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 D
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• pp.2352-2354
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• 2003

An apparatus and method for imposing a desired average radial force on tire by calculating the current average force between the tire and load wheel based on the average radial force and radial distance between the tire load wheel over the last previous complete revolution of the tire, the spring constant of the tire and the current radial distance between the tire and the load wheel.