• 융합보안논문지
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• 제11권1호
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• pp.25-32
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• 2011

본 연구에서는 소프트웨어 제품을 개발하여 테스팅을 하는 과정에서 소프트웨어 관리자들이 소프트웨어 및 검사 도구에 효율적인 학습기법을 이용한 NHPP 소프트웨어 모형에 대하여 연구 하였다. 적용분포는 와이블 분포를 적용한 유한고장 NHPP에 기초하였다. 소프트웨어 오류 탐색 기법은 사전에 알지 못하지만 자동적으로 발견되는 에러를 고려한 영향요인과 사전 경험에 의하여 세밀하게 에러를 발견하기 위하여 테스팅 관리자가 설정해놓은 요인인 학습효과의 특성에 대한 문제를 비교 제시 하였다. 그 결과 학습요인이 자동 에러 탐색요인보다 큰 경우가 대체적으로 효율적인 모형임을 확인 할 수 있었다. 본 논문의 수치적인 예에서는 고장 간격 시간 자료를 적용하고 모수추정 방법은 최우추정법을 이용하고 추세분석을 통하여 자료의 효율성을 입증한 후 평균자승오차와 $R_{sq}$(결정계수)를 이용하여 효율적인 모형을 선택 비교하였다.

• 한국전자통신학회논문지
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• 제18권5호
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• pp.867-876
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• 2023

본 연구에서는 감마족 분포(Erlang, Log-Logistic, Rayleigh)을 적용한 NHPP 소프트웨어 개발 비용 모형의 속성을 새롭게 분석하였고, 모형의 속성을 검증하기 위해 Goel-Okumoto 기본 모형과 비교한 후, 이를 근거로 최적의 모형도 제시하였다. 소프트웨어 신뢰도를 분석하기 위하여 시스템 운영 중 랜덤하게 발생한 고장 시간 데이터를 활용하였고, 모수의 계산은 최우추정법을 사용하여 해결하였다. 다양한 속성 분석(평균값 함수, 개발 비용, 최적의 방출시간)을 통하여 종합적으로 평가한 결과, Rayleigh 모형이 가장 우수한 성능을 가진 모형임을 확인하였다. 본 연구를 통하여, 기존 연구 사례가 없는 감마족 분포를 적용한 소프트웨어 개발비용 모형의 속성을 새롭게 규명하였다. 또한, 개발자들이 초기 단계에서 본 연구 데이터를 효율적으로 활용할 수 있도록 기초적인 설계 데이터도 제시할 수 있었다.

• 한국산학기술학회논문지
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• 제21권11호
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• pp.884-891
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• 2020

교량은 현대 사회에서 중요한 사회기반시설물 중에 하나로 교량의 붕괴는 막대한 인명 피해와 경제적 손실을 일으킬 수 있다. 따라서 교량의 구조적 안전성을 평가하는 것은 매우 중요하며, 이를 위해 교량을 둘러싼 여러 종류의 불확실성 요인들을 고려하는 구조신뢰성 해석이 흔히 사용된다. 본 연구에서는 다양한 하중 조건에서 교량의 안전성을 평가하기 위한 새로운 구조신뢰성 해석 플랫폼을 제안한다. 제안 플랫폼 FERUM-MIDAS는 신뢰성 해석 소프트웨어인 Finite Element Reliability Using MATLAB(FERUM)과 교량 설계/해석에 특화된 상용 소프트웨어인 MIDAS/CIVIL을 연결하여, 자동적인 입출력 데이터 교환을 통해서 구조신뢰성 해석을 수행한다. 나아가 MIDAS/CIVIL의 그래픽 사용자 인터페이스로만 소프트웨어 구동이 가능한 한계점을 극복하기 위하여 FERUM에 별도의 그래픽 사용자 인터페이스 제어 모듈을 추가하였다. 본 연구에서는 제안 플랫폼을 간단한 프레임 예제에 적용하여 대표적인 신뢰성 해석 방법인 FORM(First-Order Reliability Method)과 MCS(Monte Carlo simulation)의 해석 결과를 비교·분석하였으며, 계산된 파괴확률 차이가 5% 미만인 것을 확인하여 제안 플랫폼의 검증을 완료하였다. 이와 더불어 개발된 플랫폼을 활용하여 KL-510 활하중 모델을 고려한 프리스트레스트 콘크리트(pre-stressed concrete, PSC)교의 파괴확률과 신뢰도 지수를 도출하고, 그 결과를 분석하여 교량의 구조적 안전성을 평가하였다. 본 연구에서 제안한 새로운 구조신뢰성 해석 플랫폼을 통해 교량의 효과적인 신뢰도 기반 안전성 평가가 가능할 것으로 기대된다.

• Structural Engineering and Mechanics
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• 제64권4호
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• pp.413-426
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• 2017

Probabilistic methods are used in engineering where a computational model contains random variables. The proposed method under development: Direct Optimized Probabilistic Calculation (DOProC) is highly efficient in terms of computation time and solution accuracy and is mostly faster than in case of other standard probabilistic methods. The novelty of the DOProC lies in an optimized numerical integration that easily handles both correlated and statistically independent random variables and does not require any simulation or approximation technique. DOProC is demonstrated by a collection of deliberately selected simple examples (i) to illustrate the efficiency of individual optimization levels and (ii) to verify it against other highly regarded probabilistic methods (e.g., Monte Carlo). Efficiency and other benefits of the proposed method are grounded on a comparative case study carried out using both the DOProC and MC techniques. The algorithm has been implemented in mentioned software applications, and has been used effectively several times in solving probabilistic tasks and in probabilistic reliability assessment of structures. The article summarizes the principles of this method and demonstrates its basic possibilities on simple examples. The paper presents unpublished details of probabilistic computations based on this method, including a reliability assessment, which provides the user with the probability of failure affected by statistically dependent input random variables. The study also mentions the potential of the optimization procedures under development, including an analysis of their effectiveness on the example of the reliability assessment of a slender column.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.245-248
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• 2000

Modern aircraft composite structures are designed using a damage tolerance philosophy. This design philosophy envisions sufficient strength and structural integrity of the aircraft to sustain major damage and to avoid catastrophic failure. The only reasonable way to treat on the same basis all the conditions and uncertainties participating in the design of damage tolerant composite aircraft structures is to use the probability-based approach. Therefore, the model has been developed to assess the probability of structural failure (POSF) and associated risk taking into account the random mechanical loads, random temperature-humidity conditions, conditions causing damages, as well as structural strength variations due to intrinsic strength scatter, manufacturing defects, operational damages, temperature-humidity conditions. The model enables engineers to establish the relationship between static/residual strength safety margins, production quality control requirements, in-service inspection resolution and criteria, and POSF. This make possible to estimate the cost associated with the mentioned factors and to use this cost as overall criterion. The methodology has been programmed into software.

• Nuclear Engineering and Technology
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• 제55권4호
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• pp.1528-1539
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• 2023

Since the leakage of sodium in an SFR (sodium-cooled fast reactor) causes an explosion upon reaction with air and water, sodium leakages represent an important safety issue. In this study, a novel technique for improving the reliability of sodium leakage detection applying DDVR (dynamic data validation and reconciliation) is proposed and verified to resolve this technical issue. DDVR is an approach that aims to improve the accuracy of a target system in a dynamic state by minimizing random errors, such as from the uncertainty of instruments and the surrounding environment, and by eliminating gross errors, such as instrument failure, miscalibration, or aging, using the spatial redundancy of measurements in a physical model and the reliability information of the instruments. DDVR also makes it possible to estimate the state of unmeasured points. To validate this approach for supporting sodium leakage detection, this study applies experimental data from a sodium leakage detection experiment performed by the Korea Atomic Energy Research Institute. The validation results show that the reliability of sodium leakage detection is improved by cooperation between DDVR and hardware measurements. Based on these findings, technology integrating software and hardware approaches is suggested to improve the reliability of sodium leakage detection by presenting the expected true state of the system.

• Structural Engineering and Mechanics
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• 제85권3호
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• pp.407-417
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• 2023

Precast assembled bridge piers with hybrid connection (PASP) use both tendons and socket connections. To study the seismic performance of PASP, a full-scale in-situ test was performed based on an actual bridge project. The elastic-plastic fiber model of PASP was established using finite element software, and numerical analyses were performed to study the influence of prestress degree and socket depth on the PASP seismic performance. The results show that the typical failure mode of PASP under horizontal load is bending failure dominated by concrete cracking at the joint between the column and cushion cap. The cracking of the pier concrete and opening of joints depend on the prestress degree and socket depth. The prestressing tendons and socket connection can provide enough ductility, strength, restoration capability, and bending strength under small horizontal displacements. Although the bearing capacity and post yield stiffness of the pier can be improved to some extent by increasing the prestressing force, ductility is reduced, and residual deformation is increased. Overall, there are reasonable minimum socket depths to ensure the reliability of the socket connection.

• Nuclear Engineering and Technology
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• 제55권1호
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• pp.119-130
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• 2023

Among the various elements of probabilistic safety assessment (PSA), human failure events (HFEs) and their dependencies are major contributors to the quantification of risk of a nuclear power plant. Currently, the dependency among HFEs is reflected using a post-processing method in PSA, wherein several drawbacks, such as limited propagation of minimal cutsets through the fault tree and improper truncation of minimal cutsets exist. In this paper, we propose a method to model the HFE dependency directly in a fault tree using the if-then-else logic. The proposed method proved to be equivalent to the conventional post-processing method while addressing the drawbacks of the latter. We also developed a software tool to facilitate the implementation of the proposed method considering the need for modeling the dependency between multiple HFEs. We applied the proposed method to a specific case to demonstrate the drawbacks of the conventional post-processing method and the advantages of the proposed method. When applied appropriately under specific conditions, the direct fault-tree modeling of HFE dependency enhances the accuracy of the risk quantification and facilitates the analysis of minimal cutsets.

• Structural Engineering and Mechanics
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• 제66권4호
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• pp.423-438
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• 2018

This pioneer study focuses on finite element modeling and numerical modeling of three types of Reinforced Concrete Haunched Beams (RCHBs). Firstly, twenty RCHBs, consisting of three types, and four prismatic beams which had been tested experimentally were modeled via a nonlinear finite element method (NFEM) based software named as, ATENA. The modeling results were compared with experimental results including load capacity, deflection, crack pattern and mode of failure. The comparison showed a good agreement between the results and thus the model used can be effectively used for further studies of RCHB with high accuracy. Afterwards, new mechanism modes and design code equations were proposed to improve the shear design equation of ACI-318 and to predict the critical effective depth. These equations are the first comprehensive formulas in the literature involving all types of RCHBs. The statistical analysis showed the superiority of the proposed equation to their predecessors where the correlation coefficient, $R^2$ was found to be 0.89 for the proposed equation. Moreover, the new equation was validated using parametric and reliability analyses. The parametric analysis of both experimental and predicted results shows that the inclination angle and the compressive strength were the most influential parameters on the shear strength. The reliability analysis indicates that the accuracy of the new formulation is significantly higher as compared to available design equations and its reliability index is within acceptable limits.

• Advances in aircraft and spacecraft science
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• 제4권1호
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• pp.53-64
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• 2017

Aerospace Launch Vehicles (ALV) are generally designed with high reliability to operate in complete security through fault avoidance practices. However, in spite of such precaution, fault occurring is inevitable. Hence, there is a requirement for on-board fault recovery without significant degradation in the ALV performance. The present study develops an advanced fault recovery strategy to improve the reliability of an Aerospace Launch Vehicle (ALV) navigation system. The proposed strategy contains fault detection features and can reconfigure the system against common faults in the ALV navigation system. For this purpose, fault recovery system is constructed to detect and reconfigure normal navigation faults based on the sliding mode observer (SMO) theory. In the face of pitch channel sensor failure, the original gyro faults are reconstructed using SMO theory and by correcting the faulty measurement, the pitch-rate gyroscope output is constructed to provide fault tolerant navigation solution. The novel aspect of the paper is employing SMO as an online tuning of analytical fault recovery solution against unforeseen variations due to its hardware/software property. In this regard, a nonlinear model of the ALV is simulated using specific navigation failures and the results verified the feasibility of the proposed system. Simulation results and sensitivity analysis show that the proposed techniques can produce more effective estimation results than those of the previous techniques, against sensor failures.