• Nuclear Engineering and Technology
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• 제51권2호
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• pp.444-452
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• 2019

To assess the availability of a nuclear power plant's dynamic systems, it is necessary to consider the impact of dynamic interactions, such as components, software, and operating processes. However, there is currently no simple, easy-to-use tool for assessing the availability of these dynamic systems. The existing method, such as Markov chains, derives an accurate solution but has difficulty in modeling the system. When using conventional fault trees, the reliability of a system with dynamic characteristics cannot be evaluated accurately because the fault trees consider reliability of a specific operating configuration of the system. The dynamic reliability graph with general gates (DRGGG) allows an intuitive modeling similar to the actual system configuration, which can reduce the human errors that can occur during modeling of the target system. However, because the current DRGGG is able to evaluate the dynamic system in terms of only reliability without repair, a new evaluation method that can calculate the availability of the dynamic system with repair is proposed through this study. The proposed method extends the DRGGG by adding the repair condition to the dynamic gates. As a result of comparing the proposed method with Markov chains regarding a simple verification model, it is confirmed that the quantified value converges to the solution.

• Nuclear Engineering and Technology
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• 제55권3호
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• pp.801-813
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• 2023

The events at Three Mile Island in the United States brought about fundamental changes in the ways that simulation would be used in nuclear operations. The need for research simulators was identified to scientifically study human-centered risk and make recommendations for process control system designs. This paper documents the human factors research conducted at the Human Systems and Simulation Laboratory (HSSL) since its inception in 2010 at Idaho National Laboratory. The facility's primary purposes are to provide support to utilities for system upgrades and to validate modernized control room concepts. In the last decade, however, as nuclear industry needs have evolved, so too have the purposes of the HSSL. Thus, beyond control room modernization, human factors researchers have evaluated the security of nuclear infrastructure from cyber adversaries and evaluated human-in-the-loop simulations for joint operations with an integrated hydrogen generation plant. Lastly, our review presents research using human reliability analysis techniques with data collected from HSSL-based studies and concludes with potential future directions for the HSSL, including severe accident management and advanced control room technologies.

• 제어로봇시스템학회논문지
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• 제17권1호
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• pp.72-77
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• 2011

The checkpointing scheme is a well-known technique to cope with transient faults in digital systems. This paper proposes an adaptive checkpointing scheme for the reliability improvement of real-time control systems with concurrent fault detection capability. With concurrent fault detection capability the effect of transient faults are assumed to be detected with no latency. The proposed adaptive checkpointing scheme is based on the reliability analysis of an equidistant checkpointing scheme. Numerical data show the proposed adaptive scheme outperforms the equidistant scheme from a reliability point of view.

• 대한임베디드공학회논문지
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• 제7권5호
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• pp.255-265
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• 2012

A cyber-physical system(CPS) is a collection of cyber and physical components that interact with each other to achieve a particular application. Here, the CPS is emerged the reliability and security problems. Particularly, the defect of reliability in the data/control transmission under the CPS can lead to serious damage. We discuss the reliability and security problem on CPS architecture. Then we would suggest the considerations of cyber security in industrial control systems built with CPS.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1616-1625
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• 2007

Recently, embedded systems role as control systems instead of mechanical control systems in many parts of vehicles. In cases that embedded systems are used controling the electric signal, it is important to secure the reliability of a software within embedded systems. In this paper, the test platform for securing the reliability and real-time characteristic of the embedded system that controls electric signal of All Wheel Steering Control System in a Bi-modal tram is proposed. The platform is built on a HIL (Hardware In the Loop) architecture. Through the HIL platform, various vehicle conditions, driver activities and environment conditions can be successfully tested without actual driving, hence improving the reliability of the embedded system for the All Wheel Steering Control System.

• 한국CDE학회논문집
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• 제18권2호
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• pp.138-147
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• 2013

The liquefaction process system is regarded as primary among all topside systems in LNG FPSO. This liquefaction process system is composed of many types of equipment. LNG equipment on offshore plants has quite different demands on the equipment compared to traditional onshore LNG plants, so the reliability analysis of this process system needs to be performed. This study investigates how DEVS formalism for discrete event simulation can be used to reliability analysis of the liquefaction cycle for LNG FPSO. The reliability analysis method based on DEVS formalism could be better model for reflecting the system configuration than the conventional reliability analysis methods, such as fault tree analysis and event tree analysis.

• 품질경영학회지
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• 제32권4호
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• pp.125-139
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• 2004

Generally, parallel redundancy is used to improve reliability in many systems. However, redundancy increases system cost, weight, volume, power, etc. Due to limited availability of these resources, the system designer has to maximize reliability subject to various constraints or minimize resources while satisfying the minimum requirement of system reliability. This paper presents GAs (Genetic Algorithms) to solve redundancy allocation in series-parallel systems. To apply the GAs to this problem, we propose a genetic representation, the method for initial population construction, evaluation and genetic operators. Especially, to improve the performance of GAs, we develop heuristic operators (heuristic crossover, heuristic mutation) using the reliability-resource information of the chromosome. Experiments are carried out to evaluate the performance of the proposed algorithm. The performance comparison between the proposed algorithm and a pervious method shows that our approach is more efficient.

• 시스템엔지니어링학술지
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• 제12권1호
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• pp.105-112
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• 2016

An aircraft must be designed to minimize system failure rate for obtaining the aircraft safety, because the aircraft system failure causes a fatal accident. The safety of the aircraft system can be predicted by analyzing availability, reliability, and maintainability of the system. In this study, the reliability and the maintainability of the hydraulic system are analysed except the availability, and therefore the reliability and the maintainability analysis process and the results are presented for a helicopter hydraulic system. For prediction of the system reliability, the failure rate model presented in MIL-HDBK-217F is used, and MTBF is calculated by using the Part Stress Analysis Prediction and quality/temperature/environmental factors described in NPRD-95 and MIL-HDBK-338B. The maintainability is predicted by FMECA(Failure Mode, Effect & Criticality Analysis) based on MIL-STD-1629A.

• 한국전문물리치료학회지
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• 제8권3호
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• pp.35-41
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• 2001

In-shoe measurement systems allow the clinician and researcher to examine the pressure parameters within the shoe. The purpose of this study was to investigate the test-retest reliability of plantar pressures using the Parotec system over speeds and plantar regions. Seventeen healthy subjects were recruited for the study. Sampling rate was 100 Hz, and data of six variables (pressure on medial heel, lateral heel, 1st metatarsal head, 5th metatarsal head, and great toe and total impulse) were collected in four different gait speed (1.0 m/sec, 1.5 m/sec, 2.0 m/sec, and comfortable walking speed) in each day. The result indicates fair to excellent reliability between the two day test. Intraclass correlation coefficients (ICCs) ranged from .693 to .979, and range of reliability was similar depending on the speed and plantar region. In most cases, data recorded by the Parotec systems provide good evidence for the reliability.

• 제어로봇시스템학회논문지
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• 제20권4호
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• pp.443-448
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• 2014

Soft errors in memory devices that caused by radiation are the main threat from a reliability point of view. This threat can be commonly overcome with the combination of SEC (Single-Error Correction) codes and scrubbing technique. The interleaving architecture can give memory devices the ability of tolerating these soft errors, especially against multiple-bit soft errors. And the interleaving distance plays a key role in building the tolerance against multiple-bit soft errors. This paper proposes a reliability model of an interleaved memory device which suffers from multiple-bit soft errors and are protected by a combination of SEC code and scrubbing. The proposed model shows how the interleaving distance works to improve the reliability and can be used to make a decision in determining optimal scrubbing technique to meet the demands in reliability.