• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.4
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• pp.334-340
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• 2015

Engine derating is often considered for reliability benefits because lower power operation reduces its failure probability. To be derated during operation, however, the engine must be initially overdesigned. The engine overdesign is cost effective only if reliability increased from derating is enough to offset the initial increase in the development cost caused from the overdesign. The purpose of this paper is to provide an analytical model to consider a trade-off between the engine overdesign and derating. We use a logistic regression model to explain reliability growth in the number of hot firing tests for a fixed power level. Using the Transcost model with the reliability growth model, we show that 10% overdesign of Titan rocket engine decreases its development cost by about 9% and 23% depending on the reliability requirement. We also point out that such a cost reduction depends on the fuel type a rocket uses.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.1 no.1
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• pp.33-42
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• 1981

Current standard code for R.C. design consists of two conventional design parts, so called WSD and USD, which are based on ACI 318-63 and 318-71 code provisions. The safety factors of our WSD and USD design criteria which are taken primarily from ACI 318-63 code are considered to be not appropriate compared to out country's design and construction practices. Furthermore, even the ACI safety factors are not determined from probabilistic study but merely from experiences and practices. This study investigates the safety level of R.C. flexural members designed by the current WSD safety provisions based on Second Moment Reliability theory, and proposes a rational but efficient way of determining the nominal safety factors and the associated flexural allowable stresses of steel bars and concretes in order to provide a consistent level of target reliability. Cornell's Mean First-Order Second Moment Method formulae by a log normal transformation of resistance and load output variables are adopted as the reliability analysis method for this study. The compressive allowable stress formulae are derived by a unique approach in which the balanced steel ratios of the resulting design are chosen to be the corresponding under-reinforced sections designed by strength design method with an optimum reinforcing ratio. The target reliability index for the safety provisions are considered to be ${\beta}=4$ that is well suited for our level of construction and design practices. From a series of numerical applications to investigate the safety and reliability of R.C. flexural members designed by current WSD code, it has been found that the design based on WSD provision results in uneconomical design because of unusual and inconsistent reliability. A rational set of reliability based safety factors and allowable stress of steel bars and concrete for flexural members is proposed by providing the appropriate target reliability ${\beta}=4$.

• The Science & Technology
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• v.32 no.10 s.365
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• pp.86-87
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• 1999

제5차 ISSAT설계 신뢰성품질 학술회의가 지난 8월 11일부터 3일동안 미국 라스베가스에서 열렸다. 한국 대표로 참석한 부산대 산업공학과 윤영필교수는 작년에 열린 제4차 회의에도 논문을 발표했는데 그 당시 조직위원장의 요청에 따라 이번엔 그의 연구분야인 '제품의 수명시험 설계와 분석'을 독립 session으로 조직해 5편의 연구논문을 심사하고 좌장으로 참석하게 된 것이다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.616-618
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• 2003

최근 급속하게 성장하고 있는 무선 이동 통신 분야중의 한 분야가 Ad hoc 네트워크 분야일 것이다. Ad hoc 네트워크는 기존의 고정된 네트워크의 한계를 뛰어 넘는 네트워크이다. 본 연구에서는 Ad hoc 네트워크의 클러스터 기반의 라우팅 프로토콜에서의 인증에 대한 프로토콜을 멀티 계층으로 설계하였다. CBRP(Cluster Based Routing Protocol)의 라우팅 프로토콜에서는 클러스터간의 인증을 위하여 CH(Cluster Head)간의 인증을 통하여 인증을 하게 된다. CH간의 신뢰성을 위하여 MCH(Main Cluster Head)를 두어 CH간의 신뢰성을 보장함으로써 상호 클러스터간의 인증을 위한 프로토콜을 설계하였다.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.571-573
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• 2007

본 논문에서는 전력계통의 신뢰도를 확률적인 관점에서 접근하고 평가 할 수 있는 신뢰도평가 시스템의 기본 개념과 설계를 소개한다． 확률기반 신뢰도 평가시스템은 Enumeration 기반，Cumulant 기반， Monte-Carlo 시뮬레이션 기반의 세 가지 기법을 사용하여 신뢰도를 평가하도록 설계하였다．

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.6
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• pp.293-297
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• 2021

Calibration of load-resistance factors for the limit state design of front covered caisson breakwaters were presented. Reliability analysis of the breakwaters which are constructed in Korean coast was conducted. Then, partial safety factors and load-resistance factors were sequentially calculated according to target reliability index. Load resistance factors were optimized to give one set of factor for limit state design of breakwater. The breakwaters were redesigned by using the optimal load resistance factor and verified whether reliability indices larger than the target value. Finally, load-resistance factors were compared with foreign country's code for verification.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.535-545
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• 2019

The PBA of ship weapon system should be installed and operated under harsh environmental conditions and so it should be highly reliable to endure the mission profiles during its entire lifetime. In the case of PBA failure during operation, rapid maintenance is highly likely to be difficult due to problems such as supply of parts, which can have a devastating effect on the mission. In order to validate the reliability of PBA, a series of tests are performed with PBA samples, but they require time, testing facilities, samples, expenses and failure analysis if failed. The reliability of PBA is predicted on the basis of specifications such as MIL-HDBK-217F, but this specification does not take into account failure mechanisms for specific design details, environment and usage, interconnects and its characteristics that drive many failures of PBA in the field. Therefore, this study predicts the reliability of PBA using an RPA tool and proposes the RPA methodology as a validation process at the design stage. With RPA, it is now possible to achieve design validation including inherent failure mechanism, identification of weakest link, alternative design options, and test plan development.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.3
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• pp.156-162
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• 2010

When eccentric or inclined load acts on foundation of the port & harbor structures, partial safety factors of bearing capacity limit state were estimated using reliability analysis. Current Korean technical standards of port and harbor structures recommend to estimate the geotechnical bearing capacity using the simplified Bishop method. In practice, however, simple method of comparing ground reaction resistance with allowable bearing capacity has been mostly used by design engineers. While the simple method gives just one number fixed but somewhat convenient, it could not consider the uncertainty of soil properties depending on site by site. Thus, in this paper, partial safety factors for each design variable were determined so that designers do perform reliability-based level 1 design for bearing capacity limit state. For these, reliability index and their sensitivities were gained throughout the first order reliability method(FORM), and the variability of the random variables was also considered. In order to verify partial safety factors determined here, a comparison with foreign design codes was carried out and were found to be reasonable in practical design.

• Proceedings of the Korean Reliability Society Conference
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• 2000.04a
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• pp.247-253
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• 2000

본 논문은 정보 여분(Information Redundancy)에서의 에러 검출 코딩(Error Detect Coding) 기법을 이용하여 3-out-of-6 자체 검사기를 설계하고, 주기적인 코드(Frequency Coding) 주입을 통해 고장-안전 제어 논리를 모델링 했다. 고장-안전 제어 논리 모듈과 TMR(Triple Modular Redundancy)의 단일 모듈간에 대해서 신뢰성 병렬 수치 해석을 수행하였고, 이때 고장-안전 제어 논리가 기존의 하드웨어 여분 기법보다 시스템 소모비용과 기능적 오버헤드가 감소되어 기능신뢰성이 증가되는 결과를 얻었다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.619-621
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• 2003

유비쿼터스 컴퓨팅은 그 발전배경에 있어서 이동성을 강조하고 있다. 개인의 휴대 단말은 점차 작고 잘 보이지 않게 되면서 주변의 컴퓨팅 자원을 활용하는 위탁컴퓨팅 모델이 부각되고 있다. 하지만 개인의 휴대 단말이 악의적인 네트워크 환경이나 위탁컴퓨터에 대해서는 무기력한 것이 사실이다. 이를 보완하기 위해서는 휴대 단말이 신뢰할 수 있는 신뢰 그룹에게 원하는 작업을 위탁할 수 있어야 하고 서버 그룹과 클라이언트 그룹 사이의 서로 다른 기능을 제공해야 한다. 논문은 유비쿼터스 컴퓨팅 환경에서 휴대 단말인 클라이언트들이 신뢰할 수 있는 신뢰 서버들을 효율적으로 관리할 수 있는 비대칭형 그룹 관리 시스템을 설계하고 제안한다.