• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2001.02a
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• pp.84-88
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• 2001

The optimum cross-sectional area Profile of gas-cooled high-temperature superconductor (HTS) current lead is analyzed to have minimum helium boil-off rate. The conventional constant area HTS lead has much higher helium consumption than the optimum HTS lead considered in this study. The optimum HTS lead has variable cross-sectional area to have constant safety factor. An analytical formula of optimum shape of lead and temperature profile are obtained. For multi-step HTS current leads, the optimum tape lengths and minimum heat dissipation rate are also formulated. The developed formulations are applied to the Bi-2223 material, and the differences between constant area, constant safety-factor, and multi-step current leads are discussed.

• Journal of the Korean Geotechnical Society
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• v.37 no.9
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• pp.5-12
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• 2021

Pseudo-static slope stability analysis method is widely used in engineering practice to calculate the seismic factor of safety of slope subjected to earthquake ground motions. Although the dynamic analysis method is well recognized to have the primary advantage of simulating the stress-strain response of soils, it is not often used in practice because of the difficult in estimating the factor of safety. In this study, a procedure which utilizes the dynamic analysis method to extract the transient dynamic factor of safety is devleoped. This method overcomes the major limitation of the pseudo-static method, which uses an empirically determined seismic coefficient to derive the factor of safety. The proposed method is applied to a slope model and the result is compared with that of the pseudo-static method. It is shown that minimum dynamic factor of safety calculated by the dynamic analysis is slightly larger than that determined from the pseudo-static method. It is also demonstrated that the dynamic factor of safety becomes minimum when the horizontal seismic coefficient and horizontal average acceleration are maximum.

• Journal of the Korean Society of Safety
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• v.21 no.2 s.74
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• pp.107-113
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• 2006

Earthquake motion is one of the most significant influence factors on the slope stability. In this paper, an effective stress analysis with the elasto-plastic model was carried out to investigate the behavior of the slope stability subjected to the successive two strong earthquake motions, fore and main shock. The major influence of fore shock to the slope stability was considered as the existence of the residual excess pore water pressure. The paper presents the influence of the existence of the fore shock to slope stability using the numerical analyses. In conclusion, the excess pore pressure by the fore shock was not dissipated during the 7hrs of consolidation. By this residual excess pore water pressure, the factor of safety at the sliding face showed the minimum values, and the deformations of slope was large when compared with the case that considered the main shock only. Furthermore, the minimum of the factor of safety came out after the end of the earthquake motion.

• Journal of the Korean GEO-environmental Society
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• v.12 no.2
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• pp.45-53
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• 2011

Soil nailing method was often designed by the slope stability analysis based on limit equilibrium. However, in the case of shorten length of nails, although the calculated factor of safety is within the design factor of safety, the horizontal displacement of soil nailed walls occurred above the allowable limit. In this study, relationship between the load and factor of safety, and relationship between the load and displacement ratio based on the test results were analysed. From the analysed results, the relationship between factor of safety and displacement ratio was estimated. For the mobilized horizontal displacement of the walls within the serviceability limit corresponding to the displacement of less than 0.3% displacement ratio, the calculated factor of safety by limit equilibrium analysis had to satisfy above 1.35. Also, although the minimum factor of safety is estimated above 1.35, the maximum horizontal displacement is often mobilized above 0.3% of excavation height. Therefore, it is necessary to perform the numerical analysis of soil nailed walls in the case of low shear strength or high excavation.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.124-131
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• 2000

Numerical analysis of slop stability is carried out using seismic intensity, modified seismic intensity, and response seismic coefficient methods. It is found by comparing each of method that minimum safety factor precedes the required safety factor. It is also proved during analysis that most conservative method is the earthquake response analysis method, next is the response seismic coefficient method, and last one is the seismic intensity method. Usually, seismic intensity method is applied in analysis of slop stability. However, in view of safety factor, modified seismic intensity method is more conservative than seismic intensity method. Also modified seismic intensity method is appropriate when height of structure analyzed is high enough.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.369-376
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• 2009

Field investigation was performed right after the occurrence of debris flow at Jinbu area. Geomorphic and geotechnical characteristics were investigated and rain fall data were collected. Based on these data, seepage and slope stability analysis was performed to verify the behavior of ground water and factor of safety of the slope according to the rainfall intensity and time. As a results, the minimum value of factor of safety achieved in long time after the moment of maximum precipitation rate. And it is confirmed that the factor of safety is susceptible to ground water level rather than rainfall intensity.

• Proceedings of the KIPE Conference
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• 1997.07a
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• pp.393-399
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• 1997

Single-phase and three-phase AC to DC power converters are becoming frequently used for high voltage/high power applications such as telecommunications. They often require input/output transformer isolation for safety, a unity input power factor for minimum reactive power, free input harmonic currents fed back to the AC Power distribution system and, finally, high efficiency and high power density for minimum weight and volume. The proposed boost converter for power factor correction (PFC) provides an unity input power factor, low harmonic distortion and high efficiency along with reduced volume and weight. Single-phase 220VAC input/380VDC 1KW output prototype is constructed and experimental results will be verified with those of PSpice simulation.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.131-136
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• 2001

In this paper, a high-temperature superconductor(HTS) current lead operating in current sharing mode is described. The minimum heat dissipation and the optimum safety factor(cross-sectional area) is obtained analytically for partial current sharing HTS leads. It is assumed that the current lead is in conduction cooled state, and the sheath material is the alloy of silver and gold. The reduced cross-sectional area results partial current sharing state, and consequently reduces conduction heat transfer, but the Joule heat generation is increased. The optimized HTS current lead is different from the conventional copper leads. In the copper leads, the minimum heat dissipation is obtained for the zero gradient of temperature at warm end. However, the temperature gradient at warm end is not zero when the HTS lead operates at minimum dissipation state.

• Tunnel and Underground Space
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• v.24 no.5
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• pp.344-353
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• 2014

In this study, the behavior of rock pillar in the diverging area of road tunnel was assessed by using a three dimensional numerical analysis. Based on parameters affecting the behavior of rock pillar, different safety factors according to pillar width, depth and rock conditions were evaluated. It turned out that as the pillar width increases, the change curve of safety factors in accordance with depth and rock conditions shows more of the nonlinear behavior. By the assessment of the minimum safety factor, a safety factor chart on the behavior of rock pillar in the diverging area of road tunnel was suggested.

• Journal of the Korean Geosynthetics Society
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• v.14 no.2
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• pp.81-88
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• 2015

This study assessed the behavior of rock pillar in tunnel diverging area by using a three dimensional numerical analysis. Based on parameters affecting the behavior of rock pillar, this study evaluated different safety factors according to pillar width, depth and rock conditions. It turned out that as the rock pillar width increases, the change curve of safety factors in accordance with depth and rock conditions shows more of the nonlinear behavior. By the assessment of the minimum safety factor, a safety factor chart on the behavior of rock pillar in tunnel diverging area was suggested.