• 한국신뢰성학회지:신뢰성응용연구
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• 제18권2호
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• pp.130-142
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• 2018

Purpose: The purpose of this study is to introduce regression method in the presence of competing risks and to show how you can use the method with hypothetical data. Methods: Survival analysis has been widely used in biostatistics division. But the same method has not been utilized in reliability division. Especially competing risks, where more than a couple of causes of failure occur and the occurrence of one event precludes the occurrence of the other events, are scattered in reliability field. But they are not utilized in the area of reliability or they are analysed in the wrong way. Specifically Kaplan-Meier method is used to calculate the probability of failure in the presence of competing risks, thereby overestimating the real probability of failure. Hence, cumulative incidence function is introduced. In addition, sample competing risks data are analysed using cumulative incidence function along with some graphs. Lastly we compare cumulative incidence functions with regression type analysis briefly. Results: We used cumulative incidence function to calculate the survival probability or failure probability in the presence of competing risks. We also drew some useful graphs depicting the failure trend over the lifetime. Conclusion: This research shows that Kaplan-Meier method is not appropriate for the evaluation of survival or failure over the course of lifetime in the presence of competing risks. Cumulative incidence function is shown to be useful in stead. Some graphs using the cumulative incidence functions are also shown to be informative.

• Steel and Composite Structures
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• 제42권1호
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• pp.59-74
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• 2022

This study introduces a general reliability-based, performance-based design framework to design frames regarding their uncertainties and user-defined design goals. The Iterative-R method extracted from the main framework can designate a proper R (i.e., response modification factor) satisfying the design goal regarding target reliability index and pre-defined probability of collapse. The proposed methodology is based on FEMA P-695 and can be used for all systems that FEMA P-695 applies. To exemplify the method, multiple three-dimensional, four-story steel special moment-resisting frames are considered. Closed-form relationships are fitted between frames' responses and the modeling parameters. Those fits are used to construct limit state functions to apply reliability analysis methods for design safety assessment and the selection of proper R. The frameworks' unique feature is to consider arbitrarily defined probability density functions of frames' modeling parameters with an insignificant analysis burden. This characteristic enables the alteration in those parameters' distributions to meet the design goal. Furthermore, with sensitivity analysis, the most impactful parameters are identifiable for possible improvements to meet the design goal. In the studied examples, it is revealed that a proper R for frames with different levels of uncertainties could be significantly different from suggested values in design codes, alarming the importance of considering the stochastic behavior of elements' nonlinear behavior.

• International Journal of Reliability and Applications
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• 제2권3호
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• pp.199-207
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• 2001

The failure rate functions between successive failures are of concatenated form. We allow the parameters of failure rate function change after a certain failure and its fixing. We confine out attention to a model wherein the interfailure times are described by its failure rate function. We suggest an adaptive failure rate function with a change-point under the assumption that interfailure times are record value statistics from a Weibull distribution. The proposed model will be applied through a practical example of software failure data.

• Communications for Statistical Applications and Methods
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• 제20권6호
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• pp.467-474
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• 2013

It is common to measure multiple coverage metrics during software testing. Software reliability growth models and coverage growth functions have been applied to each coverage metric to evaluate software reliability; however, analysis results for the individual coverage metrics may conflict with each other. This paper proposes the virtual coverage metric of a normalized first principal component in order to avoid conflicting cases. The use of the virtual coverage metric causes a negligible loss of information.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전력기술부문
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• pp.143-146
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• 2004

This paper presents a method to improve reliability by dispersed generation (DG) installation considering load types and interruption cost. The objective functions such as power losses cost, operation cost of DGS, power buy cost and interruption cost are minimized for reliability improvement and efficient operation. The several indices for reliability evaluation are improved by dispersed generation system installation.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권6호
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• pp.577-588
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• 2016

Due to the uncertainties related to the flaw assessment parameters, such as flaw size, fracture toughness, loading spectrum and so on, the probability concept is preferred over deterministic one in flaw assessment. In this study, efforts have been made to develop the reliability based flaw assessment procedure which combines the flaw assessment procedure of BS7910 and first-and second-order reliability methods (FORM/SORM). Both crack length and depth of semi-elliptical surface crack at weld toe were handled as random variable whose probability distribution was defined as Gaussian with certain means and standard deviations. Then the limit state functions from static rupture and fatigue perspective were estimated using FORM and SORM in joint probability space of crack depth and length. The validity of predicted limit state functions were checked by comparing it with those obtained by Monte Carlo simulation. It was confirmed that the developed methodology worked perfectly in predicting the limit state functions without time-consuming Monte Carlo simulation.

• 한국철도학회논문집
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• 제3권3호
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• pp.147-153
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• 2000

The train control and monitoring system (TCMS) is an on board computer system in railway vehicles performing the control, supervisory and diagnostic functions of the complete train system. This system replaces a lot of hard-wired relays and minimizes the necessary vehicle wiring thus increasing the reliability of the train. It is also one of more important equipment on vehicle to implement much higher safety and reliability train system. We studied a software design technique of TCMS using a CASE tool that is a kind of safety critical software engineering tool (SCADE). This tool has mainly four functions such as the graphical editor, the document maker, tile automatically code generator, and the test simulator. The several functions of TCMS are implemented in this software easily programmed using a functional block diagram and a graphic programming language. We applied to automatically generated TCMS modules on the SCADE each functional block for the Standard type EMU in Korea. We performed the combination test using TCMS simulator and the running test in Seoul subway 7 Line. We proved that this technique is more useful for the software design of TCMS in urban transit

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.188-194
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• 2011

The purpose of this paper is to explain the implementation method in order to enhance stability and reliability of embedded system. In this research, Texas Instrument (TI)'s TMS570 MCU(Micro Controller Unit) is used to satisfy the standard of stability that is IEC 61508. IEC 61508 suggest SIL(Safety Integrity Level) from 1 to 4 and TMS570 is satisfied SIL3. Also, TMS570 can provide several stability functions can be used in realtime system. To use such functions, this paper suggest the solution about the defect that can be used in realtime system. In basic way TMR(Triple Modular Redundancy) suggested in addition to explain about the way to improve safety and reliability. Also this paper will suggest the method that reinforce the stability of calculation by using multiplex voter and memory.

• 전기학회논문지
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• 제58권3호
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• pp.444-449
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• 2009

This paper introduces a method to establish performance criteria of the in-house power supply system in nuclear power plants. The performance criteria of the system is presented in terms of the number of function failures and amount of the out-of-service time that can be allowed commensurate with the probabilistic safety assessment results of the nuclear power plants. To obtain the performance criteria such as reliability and availability, the functions of the system were analyzed and probabilistic assessment results were utilized. This method provides quantitative guidelines in selecting and monitoring system functions to determine an adequate level of maintenance quality in order to ensure the probabilistic goals for the safety of the nuclear power plants.

• 한국신뢰성학회지:신뢰성응용연구
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• 제3권1호
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• pp.1-12
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• 2003

A continuum structure function(CSF) is a non-decreasing mapping from the unit hypercube to the unit interval. A Barlow-Wu type CSF is a CSF whose behaviour is modeled by its underlying binary structure, which is based on the multistate structure functions suggested by Barlow and Wu(1978). As the measures of importance of a system component for a Barlow-Wu type CSF, the structural and reliability importance of a component at system level ${\alpha}$ (0< ${\alpha}$ <1) are defined and their properties are deduced. Computational results are discussed as well for illustrative purpose.