• Journal of Advanced Marine Engineering and Technology
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• 제25권6호
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• pp.1228-1236
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• 2001

In this study, CT specimens were prepared from ASTH A5l6 steel which was used for pressure vessel plates for moderate and lower temperature service. And we got the fellowing characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$ , $-30^{\circ}C$, $-60^{\circ}C$, $-80^{\circ}C$, $-100^{\circ}C$ and $-120^{\circ}C$ and in the range of stress ratio of 0.1, 0.3 by means of opening mode displacement. At the constant stress ratio, the Threshold stress intensity factor range ΔAKth in the early stage of fatigue crack growth (Region I) and stress intensity factor range $\DeltaK$ in the stable of fatigue crack growth (Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN-$\Delta$K in Region II that is, the fatigue clack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• 한국해양공학회지
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• 제14권3호
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• pp.78-83
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• 2000

In this study, CT specimens were prepared from AST SA516 Gr. 70 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at 25$^{\circ}C $, -60$^{\circ}C $, -80$^{\circ}C $ and -100$^{\circ}C $ and in the range of stress ratio of 0.05, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ${\delta} K_{th}$ in the early stage of fatigue crack growth (Region I) and stress intensity factor range $\delta $K in the stable of fatigue crack growth (Region II) were increased in proportion to descending temperature. It was assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN -$\delta $K in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It was assumed that the fatigue crack growth rate da/dN is rapid in proportion to descending temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2001년도 춘계학술발표대회 개요집
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• pp.220-223
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• 2001

In this study, CT specimens were prepared hem ASTM SA516 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -l$0^{\circ}C$ and -l2$0^{\circ}C$ and in the range of stress ratio of 0.1, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ΔK$_{th}$ in the early stage of fatigue crack growth ( Region I ) and stress intensity factor range ΔK in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN - ΔK in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region H and the cryogenic-brittleness greatly affect a material with decreasing temperature.e.greatly affect a material with decreasing temperature.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 춘계학술대회 논문집
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• pp.326-331
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• 2001

In this study. CT specimens were prepared from ASME SA5l6 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at $25^{\circ}C$, -3$0^{\circ}C$, -6$0^{\circ}C$, -8$0^{\circ}C$, -10$0^{\circ}C$ and -12$0^{\circ}C$ in the range of stress ratio of 0.1 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ΔKsub/th/ in the early stage of fatigue crack growth ( Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth ( Region II) was increased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da.dN -ΔK in RegionII, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It assumed that the fatigue crack growth rate da/dN is rapid in proportion to descend temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2001년도 추계학술대회 논문집
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• pp.264-268
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• 2001

In this study, CT specimens were prepared from spring steel(SUP9) processed shot peening which was room temperature, low temperature and high temperature experiment. And we got the following characteristics from fatigue crack growth test carried out in the environment of room, and high temperature at $25^{\circ}C,\; 50^{\circ}C, \;100^{\circ}C,\; 150^{\circ}C,\; and\; 180^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range $\DeltaK_{th}$ in the early stage of fatigue crack growth (Region I ) and stress intensity factor range $\Delta$K in the stable of fatigue crack growth (Region II) was decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• 한국해양공학회지
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• 제16권5호
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• pp.80-87
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• 2002

In this study, CT specimens were prepared from spring steel(SUP9) which was used in suspension of automobile for room temperature and low temperature service. We got the following characteristics from fatigue crack growth test carried out in the environment of room temperature and low temperature at $25^{\circ}C$, ­3$0^{\circ}C$, ­5$0^{\circ}C$, ­7$0^{\circ}C$ and ­10$0^{\circ}C$ in the range of stress ratio of 0.05 by means of opening mode displacement. The threshold stress intensity factor range ΔKth in the early stage of fatigue crack growth (Region I) and stress intensity factor range ΔK in the stable of fatigue crack growth (Region II) was decreased in proportion to descend temperature. It is assumed that the fatigue resistance characteristics and fracture strength at low temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• 대한전기학회논문지:전력기술부문A
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• 제50권7호
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• pp.340-347
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• 2001

In this Paper, we proposed a new voltage stability analysis algorithm. Using $ $ calculated by the optimal load How method(OLF), it rapidly and correctly calculates a PV curve with voltage collapse point in the stable region. OLF can calculates voltage collapse point as well as the operating point in the stable region. Specially, $ $ indicates the relative distance between voltage collapse point and the solution in the unstable region. In the study of a sample system, we verified the superiority of proposed algorithm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 B
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• pp.709-711
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• 1999

In this paper, Fuzzy Logic Controller was Designed for the Degree control of Arago's disk system. Arago's disk system is an application of Arago's disk phenomenon which is the operating principle of induction motor. Since the Arago's disk system varies to stable region. maginally stable region, unstable region according to the degree of bar respectively, it is a sutable system which can be evaluate an efficiency of the system. While an existing controller which was designed using linearized system modeling could control the system on only one operating point, fuzzy logic controller has the advantage in showing good response for multi-operating points because it does not need system modeling.

• Journal of Advanced Marine Engineering and Technology
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• 제28권4호
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• pp.641-647
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• 2004

By most sensorless speed control schemes for induction motor. the control performances in high speed range are good, but it is difficult to obtain satisfactory results in low speed region. This paper proposes a new method controlling the low and the high speed regions separately to attain the stable operation in the overall range. The current error compensation method, in which the controlled stator voltage is applied to the induction motor so that the error between stator currents of the numerical model and the actual motor can be forced to decay to zero as time proceeds. is used in the low speed region In the high speed region. the method with adaptive observer is utilized. This control strategy contains an adaptive state observer for flux estimation. The rotor speed can be calculated from the rotor flux and the motor currents. The experimental results indicate good speed and load responses from the very low speed range to the high, and also show accurate speed changing performance between the low and the high speed range.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 D
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• pp.1103-1105
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• 1997

Transient stability analysis is concerned with a power system's response to unwanted disturbance. Recently, direct method which utilize the stable region of stable equilibrium point is used to analyze transient stability This paper focuses on the controlling UEP method using the fractal behaviours. In the controlling UEP method, many algorithms are used to find controlling UEP However, the existence of fractal region gives difficulty in finding the controlling UEP. So, this paper observes the fractal feature arid introduce the fractal index to explain how much the fractal region occupies in the entire space. Using an improved algorithm from the view point of fractal index, we are going to find the controlling UEP.