• Journal of the Korea Society for Simulation
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• v.8 no.3
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• pp.77-89
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• 1999

Simulating rare events, such as probability of cell loss in ATM networks, machine failure in highly reliable systems, requires huge simulation efforts due to the low chance of occurrence. Importance Sampling (IS) has been applied to accelerate the occurrence of rare events. However, it has a drawback of effective biasing scheme to make the estimator of IS unbiased. Adaptive Importance Sampling (AIS) employs an estimated sampling distribution of IS to the system of interest during the course of simulation. We propose Nonparametric Adaptive Importance Sampling (NAIS) technique which is nonparametrical version of AIS. We test NAIS to estimate a probability of rare event in M/M/1 queueing model. Comparing with classical Monte Carlo simulation, the computational efficiency and variance reductions gained via NAIS are substantial. A possible extension of NAIS regarding with random number generation is also discussed.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1093-1101
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• 2002

Continuous fiber ceramic composites (CFCCs) have advantages over monolithic ceramics : Silicon Nitride composites are not well used for application because of their low fracture toughness and fracture strength, but CFCCs exhibit increased toughness for damage tolerance, and relatively high stiffness in spite of low specific weight. Thus it is important to characterize the fracture resistance and properties of new CFCCs materials. Tensile and flexural tests were carried out for mechanical properties and the fracture resistance behavior of a SCS6 fiber reinforced Si$_3$N$_4$ matrix CFCC was evaluated. The results indicated that CFCC composite exhibit a rising R curve behavior in flexural test. The fracture toughness was about 4.8 MPa$.$m$\^$1/2 , which resulted in a higher value of the fracture toughness because of fiber bridging. Mechanical properties as like the elastic modulus, proportional limit and the ultimate strength in a flexural test are greater than those in a tensile test. Also a numerical modeling of failure process was accomplished for a flexural test. This numerical results provided a good simulation of the cumulative fracture process of the fiber and matrix in CFCCs.

• Journal of Korean Society for Quality Management
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• v.26 no.2
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• pp.27-38
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• 1998

Consider a life testing experiment in which multiple two-component shared parallel systems are put on test, and the test is terminated at a specified number of system failures. The bivariate data obtained from such a system-level life testing can be classified into three classes: 1) the case of failed two components with known failure times, 2) the case of censored two components, and 3) the case of one censored component and the other failed component of which the failure time might be known or unknown. Under this censoring scheme and the assumption of Freund's bivariate exponential life distribution, the maximum likelihood estimators are obtained. Results of comparative studies based on Monte Carlo simulation are presented.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2004.05a
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• pp.81-85
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• 2004

This paper describes the testing facility to demonstrate the performance of the distribution class circuit breakers and switchgears and the testing methods. The field-test evaluation system consists of two parts. One is the distribution system for simulation of the condition on interruption mode of switches which are installed in the system and tested by the AFG(Artificial Fault Generator) and the thunderbolt generator just like in the real field. The other is a laboratory for confirmation or the important characteristics regarding to the insulation, gas, environment durability of equipment. For the fatal failure mode, a FMEA(Failure Modes and Effects Analysis) technique which is a kind of a structural analysis to consider a counter-plan was emploved.

• Communications for Statistical Applications and Methods
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• v.26 no.2
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• pp.191-203
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• 2019

The problem of examining how well an assumed distribution fits the data of a sample is of significant and must be examined prior to any inferential process. The observed failure time data of items are often not wholly available in reliability and life-testing studies. Lowering the expense and period associated with tests is important in statistical tests with censored data. Goodness-of-fit tests for perfect data can no longer be used when the observed failure time data are progressive Type II censored (PC) data. Therefore, we propose goodness-of-fit test statistics and a graphical method based on generalized Lorenz curve for PC data from a location-scale distribution. The power of the proposed tests is then assessed through Monte Carlo simulations. Finally, we analyzed two real data set for illustrative purposes.

• JSTS:Journal of Semiconductor Technology and Science
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• v.13 no.1
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• pp.71-78
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• 2013

In highly reliable and durable systems, failures due to aging might result in catastrophes. Aging monitoring techniques to prevent catastrophes by predicting such a failure are required. Aging can be monitored by performing a delay test at faster clocks than functional clock in field and checking the current delay state from the test clock frequencies at which the delay test is passed or failed. In this paper, we focus on test clock control scheme for a system-on-chip (SoC) with multiple clock domains. We describe limitations of existing at-speed test clock control methods and present an on-chip faster-than-at-speed test clock control scheme for intra/inter-clock domain test. Experimental results show our simulation results and area analysis. With a simple control scheme, with low area overhead, and without any modification of scan architecture, the proposed method enables faster-than-at-speed test of SoCs with multiple clock domains.

• Composites Research
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• v.34 no.6
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• pp.337-344
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• 2021

In this study, the progressive failure behavior of the composite fan blade dovetail element under tensile loading is numerically investigated through finite element(FE) simulation. The accuracy of prediction by FE simulation is verified through tensile testing. The dovetail element is one of the joints for coupling the fan blade with the disk in a turbofan engine. The dovetail element is usually made of a metal material such as titanium, but the application of composite material is being studied for weight reduction reasons. However, manufacturing defects such as drop-off ply and resin pocket inevitably occur in realizing complex shapes of the fan blade made by composite materials. To investigate the effect of these manufacturing defects on the composite fan blade dovetail element, we performed numerical simulation with FE model to compare the prediction of the FE model and the tensile test results. At this time, the cohesive zone model is used to simulate the delamination behavior. Finally, we found that FE simulation results agree with test results when considering thermal residual stress and through-thickness compression enhancement effect.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.3
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• pp.405-413
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• 2011

Defense Systems Test Center in ADD supports increasingly various missile test requirements such as higher altitude event, multi target operation and low-altitude, high velocity target tracking. In this paper, we have proposed the development of instrumentation radar tracking status simulator based on virtual reality. This simulator can predict the tracking status and risk of failure using several modeling algorithms. It consists of target model, radar model, environment model and several algorithms includes the multipath interference effects. Simulation results show that the predict tracking status and signal are similar to the test results of the live flight test. This simulator predicts and analyze all of the status and critical parameters such as the optimal site location, servo response, optimal flight trajectory, LOS(Line of Sight). This simulator provides the mission plan with a powerful M&S tool to rehearse and analyze instrumentation tracking radar measurement plan for live flight test at DSTC(Defense Systems Test Center).

• Transactions of Materials Processing
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• v.20 no.2
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• pp.167-172
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• 2011

The numerical simulation of the Forming Limit Diagram(FLD) test was carried out to calculate the limiting dome height(LDH: ISO12004-2) for aluminum alloy sheet Al6061-T6. The finite element analysis was used as an effective method for evaluating formability and diagnosing possible production problems in sheet stamping operations. To predict fracture during the stamping process, several failure models such as Cockcroft-Latham, Rice-Tracey, Brozzo and ESI-Wilkins-Kamoulakos(EWK) criteria were applied. The predicted results were discussed and compared with the experiments for Al6061-T6.

• Communications for Statistical Applications and Methods
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• v.23 no.1
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• pp.57-70
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• 2016

Type-II progressive censoring is one of the censoring methods frequently used in clinical studies, reliability trials, quality control of products and industrial experiments. Sometimes in Type-II progressive censoring experiments, the failure rate is low so the waiting time to observe the $m^{th}$ failure will be very long; however, the experimenter may have to terminate the experiment before a predetermined time. In this article, if two generalized types of Type-II progressive censoring are reminded, we then make some changes in the removal method of Type-II progressive censoring such that without reducing the deduction quality, the termination time of the experiment decreases. This can be done with decreasing withdraws throughout the steps of the experiment with a special reasonable method. A simulation study is done and the results are tabulated at the end of this article for a comparison between introduced method and Type-II progressive censoring.