• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.10
• /
• pp.1227-1234
• /
• 2012

In this study, fatigue tests were carried out using real-scale pipe bend specimens with wall-thinning defects under a cyclic bending load together with a constant internal pressure of 10 MPa. The wall-thinning defect was located at the extrados and the intrados of the pipe bend specimens. A fully reversed cyclic in-plane bending displacement was applied to the specimens. For the pipe bends with wall thinning at the extrados, an axial crack occurred at the crown of the pipe bend rather than at the extrados where the defect was located. In addition, the fatigue life was longer than that of a sound pipe bend predicted from the design fatigue curve in ASME Sec.III, and it was less dependent on the axial length of the wall-thinning defect. For the pipe bends with wall thinning at the intrados, a circumferential crack occurred at the intrados. In this case, the fatigue life was much shorter than that of a sound pipe bend predicted from the design fatigue curve, and it clearly decreased with decreasing axial length of the wall-thinning defect.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.1
• /
• pp.373-379
• /
• 2020

This study performed stress and fatigue life analysis of the damping hinge of a built-in side-by-side refrigerator that occurs when the door is opened to the maximum angle. An analysis of the initial design showed that stress concentration occurred at the corner between the cylinder and upper disk of the bracket pin, and the maximum stress exceeded the yield strength. The maximum stress location and the calculated fatigue life were consistent with the door opening-and-closing endurance test results for a prototype. Three cases of design improvement for the bracket pin were derived with the aim of reducing the stress concentration that appeared in the initial design. An analysis of the cases showed that inserting a fillet between the disk and the cylinder of the bracket pin reduced the stress and increased the fatigue life. Moreover, changing the disk into two steps was more favorable. In conclusion, the best design improvement was the case that the disk was changed to two steps and the fillet with a large radius was inserted. In that case, the stress was the smallest and the fatigue life was infinite.

• 한국항공운항학회:학술대회논문집
• /
• 2016.05a
• /
• pp.136-141
• /
• 2016

본 논문에서는 항행안전시설을 구성하는 구성요소를 체계별로 구분하고 체계별 운영시간 에 따른 고장율 등을 분석한다. 아울러 설계수명에 점차 도달한 항행안전시설 운영단계에서 발생한 유지보수비용 데이터를 토대로 남은 설계수명 기간 동안 향후 발생 가능한 유지보수 비용을 추정한다. 이런 분석결과를 통해 장비의 신뢰성 관련 선행연구들에서 주로 인용되고 있는 욕조커브(Bathtub Curve) 이론과 본 연구의 비용예측 결과와의 연관성을 진단하고 안정적인 유지보수를 위한 기초자료로서 활용되고자 한다. ARIMA 예측모형을 토대로 향후 10개월 간 발생가능한 유지보수 비용을 예측한 결과 비용이 상승할 것이라는 통계적으로 신뢰할 만한 추정 결과를 얻었다. ARIMA를 활용한 추정결과는 앞선 MTBF 분석내용을 지지함과 동시에 시설의 정비 신뢰도를 보여주는 욕조커브 분포와 일치하는 신뢰할 수 있는 결론을 얻은 것이다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.04a
• /
• pp.318-321
• /
• 1995

원자력 발전소의 안전성 보장 및 신뢰성 향상을 위하여 시운전 단계에서 원자력 발전소내 안전등급에 해당하는 배관계통의 상태 확인을 위하여 각종시험을 하도록 되어있다. 특히 새로운 설계기념, 크기 또는 용량을 갖는 원자로 모델에 대해서는 필수적으로 건전성 평가를 하게 되었다. 이를 위해 발전소 건설기간에 시행하는 고온 기능시험 중에 원자로 주변 주요 시스템인 원자로 냉각재 루프 계통에 대한 건전성 확인을 위해 압전형 고온 가속도 센서를 이용하여 정상운전상태의 진동을 측정하여 시스템 진동거동을 규명하였다. 배관시스템의 일상운전상태는 유체의 흐름과 기기운전이 일정한 정상상태와 펌프의 기동 또는 정지 및 밸브의 급격한 개폐등으로 발생하는 과도상태로 나눌 수 있다. 따라서 두 가지 상태의 진동을 측정해야 한다. 배관계통은 정상운전 상태로 설계수명을 유지할 수 있어야 하므로 정상진도잉 최소화 되어야 한다. 진동 평가기준은 배관재질의 응력(S/N 커브) 곡선을 참조하여 설계수명내에 손상이 일어나지 않도록 재료의 허용응력을 산정하고 이를 진동변위로 환산하여 정한 것이며 이 값에 측정 데이타를 비교하여 1차계통 배관의 건전성을 확인하였다.

• Aerospace Engineering and Technology
• /
• v.1 no.1
• /
• pp.55-64
• /
• 2002

A conceptual design of propulsion system for a geosynchronous communication satellite with 12 years design life is presented in this paper. Propellant mass budget for the design life is calculated using total velocity increment (ΔV) flowed-down from mission requirement analysis. Sizes of the fuel and oxidizer tank are derived based on the calculated propellant mass budget, and mass of the pressurant as well as the size and pressure of pressurant tank are calculated too. Thruster positioning, number of rocket engines, and position of tank are determined through Trade-Off Study with Structure & Mechanical Subsystem. Propulsion system configuration and its schematics are presented finally.

• Aerospace Engineering and Technology
• /
• v.13 no.2
• /
• pp.160-166
• /
• 2014

The shutoff valve of a Liquid Rocket Engines (LRE) controls the flow of propellant between turbo-pump and combustion devices of LRE using pilot pressure and spring force. The shutoff valve is closed when the pilot pressure is removed from the diaphragm type actuator. During designing process of life cycle is when should be analyzed according to the characteristics of forces with respect to the opening and closing of diaphragm actuator. A valve has been designed to adjust the control pressure which is required to open a poppet and to determine the working fluid pressure at which a valve starts to close. During flow capacity test under room temperature as a part of life cycle tests, the leakage in diaphragm was occurred due to the leakage of sheet welding sections. The operating cycle of the diaphragm type actuator is about 61 times with 22 MPa of pilot pressure.

• Proceedings of the KIEE Conference
• /
• 2009.04a
• /
• pp.67-69
• /
• 2009

수십년 간 주요 운송 수단의 한가지로 사용되고 있는 도시철도는, 사고 발생 시 큰 경제적 손실과 사회적 손실을 야기할 수 있으나, 사고의 주 원인 중 한가지인 도시철도 전력설비 고장에 대한 감시 및 진단 시스템은 적용되고 있지 않은 실정이다. 최근 이러한 전력설비 상태 감시 및 진단에 대한 필요성이 점차 커지게 되어, 도시철도 전력설비 수명예측 시스템 설계에 관한 연구 과제가 제안되어 현재 국토해양부와 건설기술평가원, 그리고 한국철도기술연구원의 주도 하에 수행되고 있다. 본문에서는 수명예측 시스템 설계에 필요한 도시철도 전력 시스템의 특성과 고장 사례를 조사하였으며, 각 도시철도 운영기관의 사용자 요구사항 설문 결과, 그리고 수명예측 시스템의 일부인 전력설비 감시진단 시스템 기초 설계 결과를 나타내었다.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.3 no.3
• /
• pp.47-52
• /
• 1999

Fatigue test is an essential procedure in the dynamic structure design. It is performed to confirm that the structure should safety the required life. In this study, fatigue life for 750㎾ class horizontal axis wind turbine composite blade was investigated. Required fatigue stress was calculated by fan Bond's empirical equation and S-N linear damage method. Fatigue load for FEM analysis was calculated using load spectrum through experiments and Spera's method. Service fatigue stress was obtained by FEM with the calculated fatigue load. From comparison of the fatigue stresses, fatigue life over 20 years was confirmed.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.4
• /
• pp.495-499
• /
• 2010

In this paper, the regulatory guidelines for the continued operation of the CANDU reactor in Korea were introduced. Wolsong Unit 1, which is a CANDU 600 reactor in Korea, will reach its design life of 30 years in 2012. A licensee who wants to operate a nuclear power plant beyond its design life should submit reports of periodic safety reviews (PSRs) conducted on the basis of 11 safety factors. In addition, the licensee should provide the following: (1) scoping and screening results for aging management, (2) aging management program, (3) TLAA, including the continued operation term, (4) operation-experience feedback, and (5) important safety-research results. In this study, 54 regulatory guidelines for the five above-mentioned items for the CANDU reactor in Korea were developed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.2
• /
• pp.101-106
• /
• 2006

The optimum design of turbine blade at minimized fatigue life can be derived by the statistical fatigue analysis in this study, The optimum value of positions in the axes of X and Y at turbine blade can be found by design of experiments on the condition that the value of fillet radius is fixed to minimize the fatigue life. The degree of uncertainty about process at the factors in the axes of X and Y can be calculated by six sigma analysis. The optimum value of fillet radius is determined by utilizing the robust design at uncertain condition. It is concluded that maximum von Mises stress can decreased by 20% and the fatigue life can be double.