• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.5
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• pp.285-295
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• 2004

The outage cost assessment has an important position for determination of the optimal level or optimal range of reliability for power system expansion planning. Establishing the worth of service reliability is a very difficult and subjective task. While the utility cost(reliability cost) will generally increase as consumers are provided with higher reliability, the consumer costs(reliability worth) associated with supply interruptions will decrease as the reliability increases. The total costs to society are the sum of these two individual costs and the optimum or target level of reliability is achieved at minimum point of the total cost curve. This paper addresses the role, need and assessment algorithms and methodologies of the outage cost in power system expansion planning. In a case study, the outage cost has been assessed using macro approach for our country 15years(1986-200l) in the case study. Additionally, determination processing of optimum reliability level is presented in another case study with the five buses MRBTS.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.8
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• pp.1318-1326
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• 2008

This paper proposes an alternative methodology for deciding an optimum deterministic reliability level (IRR; Installed Reserve Rate) by using probabilistic reliability criterion (LOLE; Loss of Load Expectation). Additionally, case studies using the proposed method induce the characteristics of relationship between the probabilistic reliability index (LOLE) and deterministic reliability index (IRR) for 2008 and 2010 years in Korea power system. The case study presents a possibility that an optimum IRR level in Korea can be assessed using the proposed method. Korea power system has been using the LOLE criterion to determine the adequacy of installed capacity (ICAP) requirement. The criterion in Korea is that the loss of load expectation shall not exceed the available capacity more than five day in ten years (=0.5[days/year]), The probabilistic reliability evaluation and production cost simulation program which is called PRASim is used in order to evaluate the relationship and optimum IRR in this paper.

• International Journal of Automotive Technology
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• v.6 no.3
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• pp.235-242
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• 2005

This study introduces the Reliability-Based Design Optimization (RBDO) to enhance the kinematic and compliance (K & C) characteristics of automotive suspension system. In previous studies, the deterministic optimization has been performed to enhance the K & C characteristics. Unfortunately, uncertainties in the real world have not been considered in the deterministic optimization. In the design of suspension system, design variables with the uncertainties, such as the bushing stiffness, have a great influence on the variation of the suspension performances. There is a need to quantify these uncertainties and to apply the RBDO to obtain the design, satisfying the target reliability level. In this research, design variables including uncertainties are dealt as random variables and reliability of the suspension performances, which are related the K & C characteristics, are quantified and the RBDO is performed. The RBD-optimum is compared with the deterministic optimum to verify the enhancement in reliability. Thus, the reliability of the suspension performances is estimated and the RBD-optimum, satisfying the target reliability level, is determined.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.103-104
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• 2008

This paper proposes an alternative methodology for deciding an optimum deterministic reliability level (IRR; Installed Reserve Rate) by using probabilistic reliability criterion (LOLE; Loss of Load Expectation). Additionally, case studies using the proposed method induce the characteristics of relationship between the probabilistic reliability index (LOLE) and deterministic reliability index (IRR) for 2008 year in Korea power system. The case study presents a possibility that an optimum IRR level in Korea can be assessed using the proposed method. Korea power system has been using the LOLE criterion to determine the adequacy of installed capacity (ICAP) requirement. The criterion in Korea is that the loss of load expectation shall not exceed the available capacity more than five day in ten years (=0.5[days/year]). The probabilistic reliability evaluation and production cost simulation program which is called PRASim is used in order to evaluate the relationship and optimum IRR in this paper.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.5
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• pp.799-807
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• 2020

This paper deals with identification of probabilistic design using reliability based robust optimization in structure design of automatic salt collector. The thickness sizing variables of main structure member in the automatic salt collector were considered the random design variables including the uncertainty of corrosion that would be an inevitable hazardousness in the saltern work environment. The probabilistic constraint functions were selected from the strength performances of the automatic salt collector. The reliability based robust optimum design problem was formulated such that the random design variables were determined by minimizing the weight of the automatic salt collector subject to the probabilistic strength performance constraints evaluating from reliability analysis. Mean value reliability method and adaptive importance sampling method were applied to the reliability evaluation in the reliability based robust optimization. The three sigma level quality was considered robustness in side constraints. The probabilistic optimum design results according to the reliability analysis methods were compared to deterministic optimum design results. The reliability based robust optimization using the mean value reliability method showed the most rational results for the probabilistic optimum structure design of the automatic salt collector.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.211-214
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• 2005

This research studied robust design of composite structure under combined loading of bending and torsion. DOE (Design of Experiment) technique was used to find important design factors. The results show that the beam height, beam width, layer thickness and stack angle of outer-layer are important design parameter. The $2^{nd}$ DOE and RSM (Response Surface Model) were conducted to obtain optimum design. Multi-island genetic algorithm was used to optimum design. An approximate value of 6.65 mm in deflection was expected under optimum condition. Six sigma robust design was conducted to find out guideline for control range of design parameter. To acquire six sigma level reliability, the sigma level reliability, the standard deviation of design parameter should be controlled within 2.5 % of average design value.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.840-845
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• 2004

The reliability analysis for nonnormal distributions using the three level DOE(design of experiments) method was developed by Seo and Kwak in 2002. Although this method estimates only up to the first four moments(mean, standard deviation, skewness, and kurtosis) of the system response function, the result and the type of probability distribution determined by using the Pearson system are shown very good. However the accuracy is low in case of nonlinear performance function and sometimes, the level calculated is outside of the region in which the random variable is defined. In this article we suggest a modified three level DOE method to overcome these weaknesses and to obtain optimum choice for 3 levels and weights to handle nonnormal distributions. Furthermore we extend it to finding the optimum choice for 5 levels and weights to increase the accuracy in case of nonlinear performance function. A systematic procedure for reliability analysis is then proposed by using the Pearson system.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1090-1097
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• 2008

This study conducted the decision method of lateral flow in abutment structures founded on the soft soils and the reliability analysis on the foundation pile for abutment. On the basis of the results, this study proposed the reliability design model. Reliability analysis was conducted by applying second moment method, point estimation method, and expected total cost minimization to lateral movement index, lateral movement decision index, modified lateral movement decision index, and circular failure safety factor for the decision criteria of lateral flow. The reliability index by analysis method had a similar tendency each other. Point estimation method was found as a practical method in the aspect of convenience because it could conduct the analysis only by mean and standard deviation as well as the partial derivative on random variables was not necessary. Optimum reliability index and optimum safety according to increasing in failure factors and load ratio were analyzed and loads and resistance factors of the design criteria of optimum reliability were estimated. It presented rational design model which can consider construction level and stability and economical efficiency overall.

• Structural Engineering and Mechanics
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• v.70 no.1
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• pp.81-96
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• 2019

In this paper, a hybrid uncertain model is applied to system reliability based design optimization (RBDO) of trusses. All random variables are described by random distributions but some key distribution parameters of them which lack information are defined by variation intervals. For system RBDO of trusses, the first order reliability method, as well as monotonicity analysis and the branch and bound method, are utilized to determine the system failure probability; and Improved (${\mu}+{\lambda}$) constrained differential evolution (ICDE) is employed for the optimization process. System reliability assessment of several numerical examples and system RBDO of different truss structures are proposed to verify our results. Moreover, the effect of different classes of interval distribution parameters on the optimum weight of the structure and the reliability index are also investigated. The results indicate that the weight of the structure is increased by increasing the uncertainty level. Moreover, it is shown that for a certain random variable, the optimum weight is more increased by the translation interval parameters than the rotation ones.

• International Journal of Reliability and Applications
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• v.15 no.1
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• pp.23-50
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• 2014

This paper deals with formulation of optimum multi-objective modified step-stress accelerated life test (ALT) plan for Burr type-XII distribution under type-I censoring. Since it is impractical to estimate only one objective parameter after conducting costly ALT tests; also, it is not desirable to assume instantaneous changes in stress levels because of limited capacity of test equipments and the presence of undesirable failure modes, therefore, an optimum multi-objective modified step-stress ALT plan has been designed. The optimal test plan consists in determining the optimum low stress level and optimal time at which stress starts linearly increasing from low stress by minimizing the weighted sum of the asymptotic variances of the maximum likelihood estimator of quantile lifetimes at design constant stress. The method developed has been illustrated using an example. Sensitivity analysis has been carried out. Comparative study has also been done to highlight the merits of the proposed model.