• Fire Science and Engineering
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• v.27 no.5
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• pp.26-31
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• 2013

In nuclear power plant, anchor bolts for pressurizer supports are sufficiently used in terms of safety reason, but field inspections have reported that some bolts exceed the limit of their allowable hardness. Because the high level of hardness may lead to failures due to the stress corrosion or fracture toughness, a regular inspection is required for the bolts in nuclear power plant. Thus, this research measures the hardness of bolts currently used in pressurizer supports and then estimates maximum allowable stresses preventing failures by stress corrosion and fracture toughness. Using the ANSYS program, the stresses of the bolts in the regular condition and accidental condition have been calculated, and the possible maximum stress has been compared with the estimated allowable stresses. From the results, the stresses of bolts in the accidental condition satisfy the allowable safety stress from the stress corrosion failure. However, in the future, it shall be needed to consider the reflection of the structure assembling method on the assembling procedure to ensure the pressurizer integrity during maintenance period time.

• Geotechnical Engineering
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• v.11 no.2
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• pp.99-106
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• 1995

Although lots of experimental studies of coal ash have been performed to study the utilization as construction materials, the environmental characteristics of coal ash are still qestionable. In this study, fly ash is examined to be classified according to Korean Environmental Standard and analized whether the batch test results are within the toler trance limit when utilized or treated as reclamation and earth work materials. The batch tests was performed to examine pH and contaminant contents. Consequently, fly ash is classified as non hazardous industrial waste. The pH value shows a strong alkalinity than the tolerance limit, but it is implied that fly ash can be used to neutralize the acid ground. All other items except pH satisfy the tolerance limit, In addition, a small quantity of additives(cement) which used to improve the poor geotechnical properties of coal ash, could decrease the pH value into the tolerance limit as well as improve strengtIL durability and permeability. It is concluded that when coal ash is used properly, there is no enviormental harmfulness as construction materials.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.10a
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• pp.724-728
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• 2001

In this study, the dielectric breakdown of epoxy composites used for transformers was experimented and then its data were simulated by Weibull distribution probability. The dielectric breakdown characteristics origin in epoxy composites were examined and various effects of dielectric breakdown on epoxy composites were also discussed. As a result, first of all, speaking of dielectric breakdown properties, the more hardener increased the stronger breakdown strength at low temperature because of cross-linked density by the virtue of ester radical. And the breakdown strength of specimens with filler was lower than it of non-filler specimens because it is believed that the adding filler forms interface and charge is accumulated in it, therefore the molecular motility is raised, the electric field is concentrated, and the acceleration of electron and the growth of electron avalanche are early accomplished. In the case of filled specimens with treating silane, the breakdown strength become much higher since this suggests that silane coupling agent improves interfacial combination and relaxs electric field concentration. Finally, from the analysis of weibull distribution, it was confirmed that as the allowed breakdown probability was given by 0.1%, the applied field value needed to be under 21.5㎹/cm.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.11
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• pp.1112-1120
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• 2009

In this paper, the authors introduced a new approach to find the target orbits of each satellite in order to establish a temporary reconnaissance constellation mission to minimize the average revisit time (ART) while satisfying the constraint on fuel limit. Two distinct problems are dealt with: the first is to reconnoiter the local area with discriminating fuel constraint the second is to reconnoiter ground moving target with same fuel constraint. A preliminary effort in applying a genetic algorithm to those problems has also been demonstrated through simulation study. The results show that current ARTs of each mission are reduced by 41% and 42%, respectively, by relocating the orbit of each satellite. Naturally, the final result may depend on satellite orbits, sensor characteristics, allowable fuel cost, thruster capability, and maneuver strategies.

• Journal of Energy Engineering
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• v.28 no.4
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• pp.29-34
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• 2019

In this study, a quantitative risk assessment was carried out for a hydrogen complex station. The complex fueling station to be evaluated was hydrogen-LPG, and the components of each station were analyzed and the risk was evaluated. The final risk is assessed by individual and societal risks, taking into account the impact of damage and the frequency of accidents. As a result of individual risk calculation for the hydrogen-LPG fueling station that is the subject of this study, the hydrogen-LPG type fueling station does not show the unacceptable hazardous area (> 1 × 10E-3) proposed by HSE. The level of individual risk for both the public and the worker is within acceptable limits. In societal risk assessment, the model to be interpreted shows the distribution of risks in an acceptable range(ALARP, As Low As Reasonably Practicable). To ensure improved safety, we recommend regular inspections and checks for high-risk hydrogen reservoirs, dispensers, tube trailer leaks, and LPG vapor recovery lines.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.2
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• pp.129-136
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• 2017

This study aims to assess the damage tolerance of the wing structure of aged aircraft with long-term service through the fatigue crack growth analysis and tests. For the fatigue-critical locations (FCL) W2 and W4 in the wing structure, the fatigue stress spectrum was derived based on a previous study. Thereafter, a crack propagation analysis for the FCLs was conducted using the commercial software $NASGRO^{TM}$. The algorithm for the fatigue stress spectrum was verified. Fatigue crack growth tests were then performed for two types of specimens: Type #1 was extracted from the wing structure of aged aircraft, and Type #2 was made of the same material as the wing structure. By comparing the experimental results of these specimens, we assessed the damage tolerance of the wing structure of aged aircraft with service time.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.4
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• pp.396-402
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• 2014

The measurement of air-borne noise in a naval ship is a crucial element. Because the noise in a naval ship interferes with a communication between crews and finally it causes to reduce the combat power. Thus, most of newly built ships have to satisfy the criteria of air-borne noise in the stage of delivery of a naval ship. In order to evaluate success or failure of criteria, uncertainty of the measurement should be considered. This study introduces the test method for the measurement of the air-borne noise in a naval ship and is concerned with the evaluation of uncertainty. The uncertainty results which was from the measurement of air-borne noise in 7 naval ships newly built satisfy the error tolerance(2dB). Therefore, it is need to reduce the error tolerance for the reliable measurement result.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.831-836
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• 1998

원자로 격납건물은 그 기능적 중요성 때문에 건설종료후 반드시 원자로 가상사고를 가정한 조건에 대해 구조적 건전성을 입증하여야 한다. 본 논문은 이러한 요건에 따라 수행된 월성 3호기 원자로 격납건물 구조건전성 시험(SIT : Structural Integrity Test)의 개요와 결과를 분석한 것으로 시험결과 월성 3호기는 설계시 고려한 허용범위내에서 거동하였으며 사고시 압력하중이 큰 경수로형 원자로와 달리 시험기간중 외기 온도 변화에 민감한 변화를 보인 것으로 확인되었다. 아울러 시험결과의 정확한 평가를 위해서는 시험전 충분한 기간동안 온도변화가 계측되어야 하며, 계측기 출력의 안정화가 계측성과의 신뢰도를 높이는 필수인자임이 확인되었다.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.11b
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• pp.663-668
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• 1996

하나로를 이용한 재료조사시험용 계장캡슐 개발에 앞서 캡슐 mock-up (96M-01K)을 제작하였으며, 이 캡슐 mock-up의 실제 하나로 조사시험공 장입시를 가정하여 강도 및 열적 건전성 평가를 수행하였다. 평가 결과 하나로 정상출력시 (30MW) 캡슐 mock-up 내 조사시료의 온도는 진공 및 heating system을 사용하여 279~473$^{\circ}C$ 범위로 조절될 수 있었으며, 목표 조사기간 동안 캡슐 mock-up은 강도적으로 허용기준을 충분히 만족함으로써 안전한 것으로 판명되었다. 향후 본 캡슐 mock-up을 이용한 노외 simulation 실험 등을 통하여 기존 캡슐 mock-up의 건전성을 확인한 후 이를 기준으로 하여 표준형 하나로 캡슐을 설계 .제작하고자 한다.

• Journal of Welding and Joining
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• v.9 no.3
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• pp.10-17
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• 1991

용접구조물에서 용접이음부가 차지하는 비율은 매우 작은 경우가 많지만 용접이음부에는 각종 초기결함(이들 결함으로부터 진전하는 피로 균열, 환경에 의한 균열등을 포함) 및 용접 초기의 부정형을 비롯해서 형상적 불연속 등에서 유기되는 국부적인 응력, 변형률의 집중, 잔류응력, 구속응력, 용접금속이 갖는 숙명적인 야금적 특성의 불균일, bond부 및 HAZ부에서의 용접열 싸이클에 의한 재질의 국부적 강도저하등 용접부의 강도를 저하시키는 인자들이 복합되기 쉽고, 용접구조물 전체의 내파괴 건전성평가에서 용접부가 파괴 강도는 매우 중요하다. 용접구조물의 설계, 시공의 목적은 소요성능의 확보에 있고 구조물이 사용중에 성능손실이나 불안정 파괴가 발생하지 않도록 하는 것이 주요요건이 될 것이다. 현재의 제강기술수준에서 볼 때 모재의 강 도보다 오히려 용접부의 강도 특히 피로강도 및 파괴 인성을 적절하고 합리적으로 평가하는 것이 매우 중요하다고 해도 과언이 아닐 것이다. 용접부의 강도를 평가하는데 있어서 용접부에 발 생하는 용접결함에 대한 평가는 매우 중요하며 이들 결함에 대한 허용결함한계를 평가하여 보수 여부 및 용접구조물의 신뢰성을 평가 할 필요가 있다.