• Journal of Magnetics
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• 제17권1호
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• pp.46-50
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• 2012

A reliability-based optimization method for electromagnetic design is presented to take uncertainties of design parameters into account. The method can provide an optimal design satisfying a specified confidence level in the presence of uncertain parameters. To achieve the goal, the reliability index approach based on the firstorder reliability method is adopted to deal with probabilistic constraint functions and a double-loop optimization algorithm is implemented to obtain an optimum. The proposed method is applied to the TEAM Workshop Problem 22 and its accuracy and efficiency is verified with reference of Monte Carlo simulation results.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.779-783
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• 2008

LRFD Resistance factors for static bearing capacity of driven steel pipe piles were calibrated in the freamework of reliability theory. Reliability analysis was performed by the First Order Reliability Method (FORM) using resistance bias factor statistics.The target reliability indices are selected as 2.0 and 2.33 for group pile case and 2.5 for single pile case, based on the reliability level of the current design practice and considering redundancy of pile group, acceptable risk level, construction quality control, and significance of individual structure.

• Structural Engineering and Mechanics
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• 제3권2호
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• pp.135-144
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• 1995

Since structural systems may fail in any one of several failure modes, computation of system reliability is always difficult. A method using numerical quadrature for computing structural system reliability with either one or more than one failure mode is presented in this paper. Statistically correlated safety margin equations are transformed into a group of uncorrelated variables and the joint density function of these uncorrelated variables can be generated by using the Maximum Entropy Method. Structural system reliability is then obtained by integrating the joint density function with the transformed safety domain enclosed within a set of linear equations. The Gaussian numerical integration method is introduced in order to improve computational accuracy. This method can be used to evaluate structural system reliability for Gaussian or non-Gaussian variables with either linear or nonlinear safety boundaries. It is also valid for implicit safety margins such as computer programs. Both the theory and the examples show that this method is simple in concept and easy to implement.

• 항공우주시스템공학회지
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• 제15권2호
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• pp.16-25
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• 2021

Reliability of fatigue strength on Aircraft Composites(GFRP) Structures was assessed in this paper. Fatigue strength of GFRP was used through the existing fatigue test data with Monte Carlo method. The S_a-N_f curve of composites fatigue strength was assumed as normal distribution and reliability was analyzed using SSIT model. Fatigue stress was designed IAW ASTM F3114-15 with special safety factor of S_sf=1.2~2.0. Reliability was calculated by analytic method and FORM. Sensitivity for the effect of mean and standard deviation of fatigue strength as well as fatigue stability was evaluated. This result can be usefully applied to reliability and fatigue design for composite structures of light weight aircraft.

• 대한기계학회논문집A
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• 제36권2호
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• pp.223-230
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• 2012

취성이 큰 재료의 강도는 일반적으로 정규분포 또는 와이블분포로 설명되어 왔으나 감마분포도적합할 수 있다. 재료의 파손이 가해진 응력의 연속된 값 중 가장 큰 값에 좌우된다면 극치분포를 적용하는 것이 합당하다. 본 논문에서는 재료강도가 감마분포를 따르며 극치분포하는 응력이 작용할 경우 응력-강도 간섭이론에 기반하여 신뢰도 계산식을 제시하였으며, 확률분포 파라미터별 신뢰도와 안전율 및 변동계수와의 관계를 통하여 신뢰도 계산식의 유효성을 입증하였다. 안전율과 변동계수에 기반한 신뢰도 예측방법으로 목표 신뢰도가 설정되었을 때 최소한 요구되는 안전율과 최대로 허용되는 응력의 변동계수를 예측할 수 있다.

• 한국안전학회지
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• 제11권1호
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• pp.16-26
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• 1996

A.Satyanarayana와 다른이들은 [1.2.5]에서 domination이론을 사용하여 네트워크의 정확한 신뢰도 계산을 위한 새로운 topologic formel을 발견하였다. 이들은 이식을 통하여 그래프 G로 표현되는 어떤 시스템이나 네트워크의 신뢰도 계산을 위하여 path 또는 k-tree를 사용한 Inclusion-Exclusion식에 나타나는 항들(=2$^{m}$ -1, m은 path나 k-tree의 수)중 서로 소거되지 않는 항들은 그래프 G의 acyclic k-부분그래프(subgraph)와 1대 1로 상응되며, cyclic-과 k-부분그래프들에 상응되는 항들은 소거되어지거나 Inclusion-Exclusion식에 나타나지 않는 -결국 신뢰도계산에 필요없는- 항들임을 밝혔다. 이들은 이성질을 이용하여 그래프 G의 정확한 신뢰도계산을 위한 빠른 알고리즘을 제시하였다. 이 알고리즘은 결국 그래프 G의 path나 k-tree를 기초로 하는 Inclusion-Exclusion식에서 나타나는 항들중 소거되지 않는 항들에 1:1로 대응하는 acyclic k-subgraph만을 찾아 신뢰도계산을 할수있게 하여 준다. 이때 acyclic k-subgraph들은 각각의 domination을 갖으며, 이들은 Inclusion-Exclusion식에서 대응되는 항의 부호들의 합과 같다. 본 논문에서는 첫째로 신뢰도계산을 위하여 주어진 어떤 그래프 G에서 G를 구성하는 선(edge)을 기초로 하는 어떤 임의로 주어진 family M(G) (예: cutset이나 path, 또는 k-tree 등의 family)에 의한 (부분)그래프의 domination에 대한 성질을 관찰하고 몇가지 식을 유도한후, k-tree의 family K(G)를 기초로 한 어떤 그래프의 domination과 Inclusion-Exclusion식과의 관계를 고찰하고, 이식의 강력함과 응용의 가능성을 A. Satyanarayana의 topologic formel의 재증명을 통하여 보인다.

• Structural Engineering and Mechanics
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• 제62권3호
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• pp.365-372
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• 2017

Reliability analysis is a probabilistic approach to determine a safety level of a system. Reliability is defined as a probability of a system (or a structure, in structural engineering) to functionally perform under given conditions. In the 1960s, Basler defined the reliability index as a measure to elucidate the safety level of the system, which until today is a commonly used parameter. However, the reliability index has been formulated based on the pivotal assumption which assumed that the considered limit state function is normally distributed. Nevertheless, it is not guaranteed that the limit state function of systems follow as normal distributions; therefore, there is a need to define a new reliability index for no-normal distributions. The main contribution of this paper is to define a sophisticated reliability index for limit state functions which their distributions are non-normal. To do so, the new definition of reliability index is introduced for non-normal limit state functions according to the probability functions which are calculated based on the convolution theory. Eventually, as the state of the art, this paper introduces a simplified method to calculate the reliability index for non-normal distributions. The simplified method is developed to generate non-normal limit state in terms of normal distributions using series of Gaussian functions.

• Smart Structures and Systems
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• 제16권2호
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• pp.367-382
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• 2015

This paper aims to conduct the reliability-based assessment of the welded joint in the orthotropic steel bridge deck by use of a mesh-insensitive structural stress (MISS) method, which is an effective numerical procedure to determine the reliable stress distribution adjacent to the weld toe. Both the solid element model and the shell element model are first established to investigate the sensitivity of the element size and the element type in calculating the structural stress under different loading scenarios. In order to achieve realistic condition assessment of the welded joint, the probabilistic approach based on the structural reliability theory is adopted to derive the reliability index and the failure probability by taking into account the uncertainties inherent in the material properties and load conditions. The limit state function is formulated in terms of the structural resistance of the material and the load effect which is described by the structural stress obtained by the MISS method. The reliability index is computed by use of the first-order reliability method (FORM), and compared with a target reliability index to facilitate the safety assessment. The results achieved from this study reveal that the calculation of the structural stress using the MISS method is insensitive to the element size and the element type, and the obtained structural stress results serve as a reliable basis for structural reliability analysis.

• 대한인간공학회:학술대회논문집
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• 대한인간공학회 1996년도 춘계학술대회논문집
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• pp.113-127
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• 1996

In Human Reliability Analysis(HRA), the uncertainties involved in many factors that affect human reliability have to be represented as the quantitative forms. Conventional probability- based human reliability theory is used to evaluate the effect of those uncertainties but it is pointed out that the actual human reliability should be different from that of conventional one. Conventional HRA makes use of error rates, however, it is difficult to collect data enough to estimate these error rates, and the estimates of error rates are dependent only on engineering judgement. In this paper, the error possibility that is proposed by Onisawa is used to represent human reliability, and the error possibility is obtained by use of fuzzy reasoning that plays an important role to clarify the relation between human reliability and human error. Also, assuming these factors are connected to the top event through Fault Tree structure, the influence and correlation of these factors are measured by fuzzy operation. When a fuzzy operation is applied to Fault Tree Analysis, it is possible to simplify the operation applying the logic disjuction and logic conjuction to structure function, and the structure of human reliability can be represented as membership function of the top event. Also, on the basis of the the membership function, the characteristics of human reliability can be evaluated by use of the concept of pattern recognition.

• Journal of Magnetics
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• 제19권1호
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• pp.78-83
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• 2014

This paper proposes an efficient reliability-based optimization method for designing a superconducting magnetic energy system in presence of uncertainty. To evaluate the probability of failure of constraints, samplingbased reliability analysis method is employed, where Monte Carlo simulation is incorporated into dynamic Kriging models. Its main feature is to drastically reduce the numbers of iterative designs and computer simulations during the optimization process without sacrificing the accuracy of reliability analysis. Through comparison with existing methods, the validity of the proposed method is examined with the TEAM Workshop Problem 22.