• 품질경영학회지
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• 제23권2호
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• pp.43-52
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• 1995

A replacement policy under two types of failures, repairable or irrepairable, is considered, In the policy, the system is replaced at the n-th failure if all the previous (n-1) failures are repairable; Otherwise it is replaced at the first irrepairable failure. Assuming that the j-th failure is repairable with probability ${\alpha}_j$ and minimal repairs are performed for repairable failures between replacements, we derive the expected cost rate through the application of NHPP in order to determine the optimal number $n^*$. The policy includes some previous studies as special cases.

• 한국국방경영분석학회지
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• 제22권1호
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• pp.114-128
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• 1996

In this paper, a life distribution fitting method based on generalized phase-type distributions(GPH) is presented. By fitting the life distribution to a GPH, we can utilize various useful properties of the GPH. Two different approaches are used according to the properties of the given failure time data. One is an approximation to a GPH through the piecewise Weibull failure rate(PWF) model and the other is a direct approximation to a GPH using the empirical distribution function. Two numerical examples are also presented. In the first example, both of the two approaches are utilized and compared for an incomplete data set. And in the second example, the direct approximation method from an empirical distribution is utilized for the analysis of a complete data set. In both cases, we could confirm the validity of the proposed method.

• 대한치과보철학회지
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• 제41권6호
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• pp.714-719
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• 2003

Conical crown-retained denture (CCRD) has been used as a very effective treatment method in cases with few remaining teeth with heterogeneous prognosis. However, in spite of many advantages of CCRD, high technical failure rate was a problem to be considered. Incorrect path of insertion and excessive retention were thought to be the main cause of technical failure and to result from laboratory procedure with a coping misfit and/or a coping transfer error. In order to prevent this error, secure anchoring of inner coping and re-examination and milling of convergence angle were recommended on the master model from pick-up impression.

• 한국안전학회지
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• 제20권3호
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• pp.19-26
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• 2005

There are three reasoning method in fault diagnosis process. The shallow reasoning is based on the experiential knowledge and deep reasoning is based on physical model. Hybrid reasoning is mixing two type reasoning. This study describes about fault train embodiment of screw type air compressor that is used widely in industrial facilities by using various experimental method and shallow reasoning. We investigate macroscopic failure cause of air compressor through naked eye observation and then microscopic failure cause by various experimental method. We composed fault train with fault knowledge based on empirical data and scientific data that is acquired through several experiments. It is possible to analysis system reliability and failure rate with these fault train.

• 한국신뢰성학회지:신뢰성응용연구
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• 제17권4호
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• pp.316-324
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• 2017

Purpose: The purpose of this study is to determine the replacement cycle applied age replacement policy by reliability analysis based on railway vehicle contactor's failure history data. Method: We performed reliability analysis based on railway vehicle contactor's failure history data. We found a suitable distribution by goodness of fit test and predicted the reliability through estimation of scale & shape parameter. Considering cost information we determined the replacement cycle that minimize the opportunity cost. Result: Suitable distribution was the Weibull and scale parameter & shape parameter are estimated by reliability analysis. The replacement cycle was predicted and MTTF, $B_6$ percentile life were suggested additionally. Conclusion: We confirmed that failure rate type of railway vehicle contactor is degradation model having a time dependent characteristic and examined the replacement cycle in our country's operating environment. We expect that this study result contribute to railway operation agency for maintenance policy decision.

• 한국음향학회지
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• 제39권2호
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• pp.131-136
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• 2020

음성 인식기를 대기모드에서 동작 모드로 전환하기 위해 발화하는 짧은 단어를 기동어(Wake Up Word, WUW)라고 하며, 음성 인식기를 실제로 사용하는 사용자가 지정한 기동어를 사용자 정의 기동어라고 한다. 본 논문에서는 이러한 사용자 정의 기동어를 인식하기 위해 기존의 Gaussian Mixture Model-Hidden Markov Model(GMM-HMM) 기반의 시스템, Linear Discriminant Analysis(LDA)를 적용한 LDA-GMM-HMM 기반의 시스템과, LDA-GMM-HMM 모델에서 GMM을 Deep Neural Network(DNN)로 대체한 LDA-DNN-HMM 기반의 시스템을 제작하고 각 시스템의 사용자 정의 기동어 인식 성능 및 비기동어 거절 성능을 비교한다. 또한 기동어 인식기의 체감 성능을 향상시키고자 각 모델에 threshold를 적용하여 기동어 인식 실패율을 약 10 % 수준으로 감소 시킨 후에 비기동어(non-WUW)의 거절 실패율을 비교 평가한다. Threshold 적용시에 LDA-DNN-HMM 기반의 시스템의 경우 기동어 인식 실패율 9.84 % 수준에서 비기동어 거절 실패율이 0.0058 %의 인식 성능을 나타내어 LDA-GMM-HMM 시스템 보다 약 4.82배 향상된 비기동어 거절 성능을 나타낸다. 이러한 결과는 본 논문에서 제작한 LDA-DNN-HMM 모델이 사용자 정의 기동어 인식 시스템을 구축하는데 효과적임을 입증한다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제13권4호
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• pp.229-239
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• 2013

This paper reports a manner to use a Bayesian approach to derive the optimal replacement policy. In order to produce a system with minimal repair warranty, a replacement model with the extended warranty is considered. Within the warranty period, the failed system is minimally repaired by the manufacturer at no cost to the end-user. The failure time is assumed to follow a Weibull distribution with unknown parameters. The expected cost rate per unit time, from the end-user's viewpoints, is induced by the Bayesian approach, and the optimal replacement policy to minimize the cost rate is proposed. Finally, a numerical example illustrating to derive the optimal replacement policy based on the Bayesian approach is described.

• 한국군사과학기술학회지
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• 제17권1호
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• pp.41-49
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• 2014

In this paper, we consider a method to access the number of aircraft requirement which is a strategic variable in national security. This problem becomes more important considering the F-X and KF-X project in ROKAF. Traditionally, ATO(Air Tasking Order) and fighting power index have been used to evaluate the number of aircrafts required in ROKAF. However, those methods considers static aspect of aircraft requirement. This paper deals with a model to accommodate dynamic feature of aircraft requirement using absorbing Markov chain. In conclusion, we suggest a dynamic model to evaluate the number of aircrafts required with key decision variables such as destroying rate, failure rate and repair rate.

• Structural Engineering and Mechanics
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• 제62권6호
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• pp.663-674
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• 2017

This paper presents an approach for evaluating performance of prestressed concrete (PC) bridge girders exposed to fire. A finite element based numerical model for tracing the response of fire exposed T girders is developed in ANSYS. The analysis is carried out in three stages, namely, fire temperature calculation, cross sectional temperature evaluation, and then strength, deformation and effective prestress analysis on girders exposed to elevated temperatures. The applicability of the computer program in tracing the response of PC bridge girders from the initial preloading stage to failure stage, due to combined effects of fire and structure loading, is demonstrated through a case study, and validated by test data of a scaled PC box girder under ISO834 fire condition. Results from the case study show that fire severity has a significant influence on the fire resistance of PC T girders and hydrocarbon fire is most dangerous for the girder. The prestress loss caused by elevated temperature is about 10% under hydrocarbon fire till the girder failure, which can lead to the increase in deflection of the PC girder. The rate of deflection failure criterion is suggested to determine the failure of PC T girder under fire.

• 시스템엔지니어링학술지
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• 제10권1호
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• pp.43-48
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• 2014

The door system for railway vehicles is the critical device directly influences on safety and satisfaction of passengers, Recently, electrical type of passenger door system is widely used for EMU type train instead of pneumatic type of passenger door system. The estimation of MTBF and failure rates for electrical type door system is essential. The manufacturor simply provides intrinsic reliability data for the railway operator. But actual reliability data based on operation and maintenance data is not complying with intrinsic reliability. In this study, operation and failure data associated with electrical door system were analyzed in order to determine actual MTBF and failure data. Intrinsic reliability data and service reliability data were studied to finallize much more practical and reliable actual reliability. Relax 2011 was used to predict intrinsic reliability and 217Plus model was also used to estimate of actual reliability data based on field data. Furthermore, it is necessary to keep studying on reliability prediction methodology and applying it in the field and doing research on improvement of reliability through feedback as well.