• 대한기계학회논문집A
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• 제21권7호
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• pp.1089-1096
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• 1997

In this paper, Rancho Seco transient which is reported as a typical pressurized thermal shock event is postulated to be occuring in the Kori unit 1 plant, the oldest nuclear power plant in Korea. For the given material properties, transient history such as temperature and pressure, and postulated flaw, the stress distribution is obtained to calculate stress intensities for a wide range of assumed crack sizes. The stress intensities are compared with the fracture toughness, which is determined using the material properties and the distribution of the nil ductility transition temperature, to determine if cracking is expected to occur during the transient. The allowable operating year for the transient is determined and the evaluation results are discussed.

• 조명전기설비학회논문지
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• 제26권4호
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• pp.57-66
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• 2012

When typical Z-source DC/AC inverter(ZSI) is operated in high voltage gain area, because of its high duty ratio, voltage and current stress in Z-network of typical ZSI are increased. This paper proposes a new switched trans ZSI(STZSI) with two switched trans cells which consist of one trans and two diodes. To confirm the operation performance of the proposed system, the PSIM simulation is performed for typical ZSI, switched inductor ZSI and the proposed STZSI. Voltage / current stress and transient state characteristics of each method are compared under the condition of DC input voltage 100[V] and output phase voltage 66[Vrms]. As a result, we confirmed that transient state of the proposed STZSI is short compared with the conventional ZSI because the high voltage gain is obtained using the same duty ratio, also a low duty ratio is required for the same output voltage. Finally, we could know the proposed system have low voltage and current stress in Z-network compared with the conventional ZSI.

• Structural Engineering and Mechanics
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• 제47권3호
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• pp.421-442
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• 2013

This paper is concerned with the theoretical treatment of transient thermoelastic problems involving a functionally graded hollow cylinder with piecewise power law due to asymmetrical heating from its surfaces. The thermal and thermoelastic constants of each layer are expressed as power functions of the radial coordinate, and their values continue on the interfaces. The exact solution for the two-dimensional temperature change in a transient state, and thermoelastic response of a hollow cylinder under the state of plane strain is obtained herein. Some numerical results for the temperature change and the stress distributions are shown in figures. Furthermore, the influence of the functional grading on the thermal stresses is investigated.

• 소음진동
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• 제6권4호
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• pp.447-456
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• 1996

Dynamic characteristics of the bell-type structure including acoustic effects and transient dynamic problems were analyzed numerically. Natural frequencies, mode shapes and transient dynamic analysis used the finite element method with 3-D general shell element. Mode shapes and stress distributions of transient dynamic analysis were expressed by computer graphics. The method using this study was evaluated by comparision of theoretical results at reference papers(14), (15) and the experimental test using Fast Fourier Transform analyzer. Vibrational modes governing acoustic characteristics of the typical bell-type structure depended on the first flexural mode(4-0 mode) and the second flexural mode(6-0 mode). Asymmetric effects by Dangiwas, acoustic holes gave rise to beat frequencies, and the Dangjwa was found to be most effective. When impact load acted on the bell, stress concentration occured at the rim part of bell. It was found that the bell type structure should be designed thickly at the rim part in order to prevent impact load from stress concentration.

• 소음진동
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• 제10권2호
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• pp.306-311
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• 2000

The stress distribution of a rotating cantilever beam in transient vibration is investigated in this paper. The equations of motion of the rotating bean are derived and numerical results are obtained. The tensile and bending stresses which occur when the beam rotates with the tuned angular speed or passes through the tuned angular speed are obtained. Since those stresses are usually significant during the rotational motion, it is important to estimate them accurately in the design of the rotating structure.

• Structural Engineering and Mechanics
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• 제8권1호
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• pp.103-118
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• 1999

The structural integrity of the reactor pressure vessel under pressurized thermal shock (PTS) is evaluated in this study. For given material properties and transient histories such as temperature and pressure, the stress distribution is found and stress intensity factors are obtained for a wide range of crack sizes. The stress intensity factors are compared with the fracture toughness to check if cracking is expected to occur during the transient. A round robin problem of the PTS during a small break loss of coolant transient has been analyzed as a part of the international comparative assessment study, and the evaluation results are discussed. The maximum allowable nil-ductility transition temperatures are determined for various crack sizes.

• 전자공학회논문지
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• 제50권8호
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• pp.285-291
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• 2013

본 논문은 금속 산화물 반도체의 산화막 두께, 채널 폭과 길이에 따른 실리콘 산화막의 신뢰성 특성을 연구하였다. 스트레스전류와 전이전류는 스트레스 전압에 의하여 발생된다. 스트레스 유기 누설전류는 스트레스 전압 인가 동안과 인가 후의 실리콘 산화막에 나타난다. 이때 저레벨 스트레스 전압에 의한 저레벨 누설전류는 저전압 인가 동안과 인가 후의 얇은 실리콘 산화막에서 발생한다. 저레벨 누설전류는 각각 스트레스 바이어스 조건에 따라 스트레스전류와 전이전류를 측정하였다. 스트레스 채널전류는 일정한 게이트 전압이 인가동안 측정하였고 전이 채널전류는 일정한 게이트 전압을 인가한 후에 측정하였다. 본 연구는 소자의 구동 동작 신뢰성을 위하여 저레벨 스트레스 바이어스 전압에 의한 스트레스 전류와 전이전류가 발생되어 이러한 저레벨 누설전류를 조사하였다.

• BMB Reports
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• 제31권2호
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• pp.117-122
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• 1998

Changes of lipocortin 1 (LC1) in the brain induced by immobilization stress were investigated in rats. Rats were immobilized for 0,1,2,3,4, and 5 h, and the brain slices were immunostained with anti-human LC1 antibodl (anti-LC1). Immunoreactivity of LCI (iLC1) was most prominent in neuronal cell bodies and processes of hippocampal CA regions and dentate gyrus. At rest without stress, most of the LC1 in the neuron located in the cytoplasm with the nuclei exhibiting relatively scarce immunoreactivity. Immobilization stress changed this intracellular distribution of LC1 by increasing nuclear LC1. The change was apparent in 1 h and reached the peak by 3 h. However, by 5 h of immobilization, the distribution pattern returned to that of the resting state. This transient nuclear translocation of LC1 was most prominent in $CA_1$ pyramidal neurons, and was not observed in areas other than the hippocampus. Adrenalectomy abolished this transient translocation of LC1. The roles of hippocampal LC1 as a mediator of glucocorticoid feedback signal and/or as an intracellar stress signaling protein could be suggested.

• 대한기계학회논문집A
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• 제39권10호
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• pp.1001-1010
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• 2015

본 논문에서는 탄성-소성-크리프 상태에서 시간의존적 균열 선단 응력장을 평가하기 위해 Single-Edge-notched-Bend (SEB) 시편을 사용하여 유한요소 크리프 해석을 수행하였다. 천이크리프의 초기소성 영향을 조사하고자 다양한 초기하중을 대해 고려하였으며, 또한 소성물성과 크리프 물성의 영향을 조사하기 위해 소성 경화 지수(m)과 크리프 지수(n)이 같은 경우와 다른 경우를 모두 고려하였다. 결과로서, 기존 식의 수정을 통해서 천이크리프 상태에서의 균열 선단 응력장의 예측 식을 제안하였으며, 유한요소해석 결과와 비교를 통해서 제시된 수식의 타당성을 검증하였다. 그리고 m 과 n 이 같은 경우뿐만 아니라 m과 n이 다른 경우에도 천이크리프 상태에서 균열 선단 응력장을 예측 할 수 있는 식을 제안하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제31권8호
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• pp.998-1004
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• 2007

Connecting a synchronous generator to a power system is a dynamic process, requiring the coordinated operation of many components and systems. The goal is to connect the oncoming generator to the system smoothly i.e without causing any significant bumps, surges, or power swings, by closing the ACB when the oncoming generator matches the power system in voltage magnitude, phase angle, and frequency. If oncoming generator voltage is not matched to the power system voltage, reactive power will flow either into or out of the system at the instant of ACB closure. If this voltage difference is too great, the reactive power flow may result in high transient stresses that could damage the windings of the generator. Also, if oncoming generator frequency is not matched to the power system frequency, transient power will flow between generator and power system. If the frequency difference is too great, the transient power flow is reflected into the prime mover shaft, and this may result in excessive shaft or coupling stress. This paper tries to prove the necessity of correct synchronization for ship generators through a transient phenomenon analysis.