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Risk importance measures in the dynamic flowgraph methodology

RELIABILITY ENGINEERING & SYSTEM SAFETY 2013年第Oct.期118卷 35-50页

作者： Tyrvainen, T. VTT Tech Res Ctr Finland FI-02044 Espoo Finland

This paper presents new risk importance measures applicable to a dynamic reliability analysis approach with multi-state components. dynamic reliability analysis methods are needed because traditional methods, such as fault tree analysis, can describe system's dynamical behaviour only in limited manner. dynamic flowgraph methodology (DFM) is an approach used for analysing systems with time dependencies and feedback loops. The aim of DFM is to identify root causes of a top event, usually representing the system's failure. Components of DFM models are analysed at discrete time points and they can have multiple states. Traditional risk importance measures developed for static and binary logic are not applicable to DFM as such. Some importance measures have previously been developed for DFM but their ability to describe how components contribute to the top event is fairly limited. The paper formulates dynamic risk importance measures that measure the importances of states of components and take the time-aspect of DFM into account in a logical way that supports the interpretation of results. dynamic risk importance measures are developed as generalisations of the Fussell-Vesely importance and the risk increase factor. (c) 2013 Elsevier Ltd. All rights reserved.

关键词： dynamic flowgraph methodology Risk importance measure Multi-state

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Reliability modeling of networked control systems using dynamic flowgraph methodology

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RELIABILITY ENGINEERING & SYSTEM SAFETY 2010年第11期95卷 1202-1209页

作者： Al-Dabbagh, Ahmad W. Lu, Lixuan Univ Ontario Inst Technol Fac Energy Syst & Nucl Sci Oshawa ON L1H 7K4 Canada

The recent trend in deploying communication networks in digital control systems to form Networked Control Systems (NCSs) brings the need for utilizing dynamic methods to assess the reliability of these systems. The methods should be able to capture the behaviour and interaction of the hardware, the software and the communication network in the NCSs. They should also be able to incorporate time dependency and multi-state behaviour. In this paper, it is demonstrated how the dynamic flowgraph methodology (DFM) can be a promising method to fulfill these requirements. The behaviour and the effect of the communication network on NCS performance is emphasized. The information provided by analysis of the implemented model facilitates the improvement of the control system performance. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Reliability assessment dynamic flowgraph methodology Networked control system

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Solving dynamic flowgraph methodology models using binary decision diagrams

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RELIABILITY ENGINEERING & SYSTEM SAFETY 2013年 111卷 206-216页

作者： Bjorkman, Kim VTT Tech Res Ctr Finland FI-02044 Espoo Finland

dynamic flowgraph methodology (DFM) is a computationally challenging approach to the reliability analysis of dynamic systems with feedback loops. To improve the computational efficiency of DFM modelling, we propose a new approach, based on binary decision diagrams (BDDs), to solving DFM models. The objective of DFM analysis is to identify the root causes of a postulated top event. The result is a set of prime implicants that represent system faults resulting from diverse combinations of software logic errors, hardware failures, human errors and adverse environmental conditions. Two approaches to solving prime implicants have been implemented in software called YADRAT. The first approach is based on meta-products, and the second on zero-suppressed BDDs (ZBDD). Both approaches have been used previously in fault tree analysis. In this work, the ideas of prime implicant computations are adapted to a dynamic reliability analysis approach combined with multi-valued logic. The computational efforts required for the two approaches are compared by analysing three example systems. The results of the comparison show that BDDs are applicable in DFM computation and that in particular the ZBDD-based approach can solve moderately sized DFM models in a reasonable time. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Binary decision diagram dynamic flowgraph methodology dynamic reliability analysis Multi-valued logic Prime implicant

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Field Programmable Gate Array Reliability Analysis Using the dynamic flowgraph methodology

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NUCLEAR ENGINEERING AND TECHNOLOGY 2016年第5期48卷 1192-1205页

作者： McNelles, Phillip Lu, Lixuan Univ Ontario Inst Technol UOIT Fac Energy Syst & Nucl Sci 2000 Simcoe St North Oshawa ON L1H 7K4 Canada

Field programmable gate array (FPGA)-based systems are thought to be a practical option to replace certain obsolete instrumentation and control systems in nuclear power plants. An FPGA is a type of integrated circuit, which is programmed after being manufactured. FPGAs have some advantages over other electronic technologies, such as analog circuits, microprocessors, and Programmable Logic Controllers (PLCs), for nuclear instrumentation and control, and safety system applications. However, safety-related issues for FPGA-based systems remain to be verified. Owing to this, modeling FPGA-based systems for safety assessment has now become an important point of research. One potential methodology is the dynamic flowgraph methodology (DFM). It has been used for modeling software/hardware interactions in modern control systems. In this paper, FPGA logic was analyzed using DFM. Four aspects of FPGAs are investigated: the "IEEE 1164 standard," registers (D flip-flops), configurable logic blocks, and an FPGA-based signal compensator. The ModelSim simulations confirmed that DFM was able to accurately model those four FPGA properties, proving that DFM has the potential to be used in the modeling of FPGA-based systems. Furthermore, advantages of DFM over traditional reliability analysis methods and FPGA simulators are presented, along with a discussion of potential issues with using DFM for FPGA-based system modeling. Copyright (C) 2016, Published by Elsevier Korea LLC on behalf of Korean Nuclear Society.

关键词： dynamic flowgraph methodology Field Programmable Gate Array Instrumentation and Control Nuclear Power Plant Reliability

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Implementing dynamic flowgraph methodology models with logic programs

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PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART O-JOURNAL OF RISK AND RELIABILITY 2013年第3期227卷 302-314页

作者： Karanta, Ilkka VTT FI-02044 Espoo Finland

The dynamic flowgraph methodology is a promising way to find the prime implicants of a top event for a dynamic system possibly containing digital subsystems. This article demonstrates how to express dynamic flowgraph methodology models as logic programs, and top events as queries to those programs, in a natural and comprehensible way. Computation of the logic program lists the prime implicants of a top event in the system. We also present and implement an algorithm for computing the probability of the top event from its prime implicants. Together, computation of prime implicants and calculation of top event probability from these constitute a complete way of finding a system's failure probability. Logic programs, implemented in this article in the leading logic programming language Prolog, enable rapid prototyping of dynamic flowgraph methodology models. The logic programming framework introduced here could also be utilized in teaching dynamic flowgraph methodology in risk analysis courses.

关键词： dynamic flowgraph methodology logic programming Prolog dynamic probabilistic risk analysis

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RESEARCH ON THE RELIABILITY OF DIGITAL INSTRUMENTATION AND CONTROL SYSTEM OF NUCLEAR POWER PLANT BASED ON dynamic flowgraph methodology 25

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25th International Conference on Nuclear Engineering

作者： Chen Zhuo Zhao Bo Yang Jian Sun Jin-long CHINA NUCL POWER ENGN CO LTD Beijing Peoples R China

ISBN: (纸本)9780791857854

With the development of information and computer technology, the Digital Instrumentation and Control (I&C) System has been widely used in nuclear power plants, which leads the tendency of NPPS' construction and rebuilding on digital I&C system. As an approximate approach, conventional fault tree approach has been used quite often in the analysis of nuclear power plants' Probability Safety Assessment (PSA), which combine with system components' failure modes in order to modeling the digital system's failure. However, for the reason that conventional fault tree approach has a great disadvantage on analyzing the reliability of digital I&C system, which may not be able to fully describe the dynamic behavior of digital I&C system with significant hardware/software/human action process interaction, multi-failure modes and logic loops, it cannot carry on effective modeling and evaluation of digital I&C system. Therefore it is necessary to establish some dynamic approaches to modeling digital I&C system. As a new probability safety analysis method, dynamic flowgraph methodology (DFM) can model the relationship between time sequence and system variables because of its dynamic property. Therefore, DFM can be used to analyze the impact of software failure, hardware failure and external environment, which are closely related to the reliability of the whole system. In the first place, this paper introduces the theoretical basis, model elements and the modeling procedures of DFM and demonstrates how dynamic flowgraph methodology (DFM) can be applied to Reactor Protection System with interactions between hardware/software and physical properties of a controlled process. Meanwhile, in this case, DFM and fault tree methodologies are both used to conduct the PSA for the same top event by calculating the probability of it and finding out the prime implicants of DFM and minimal cutsets of conventional fault tree. During the process of analysis, we mainly evaluate the reliability of rea

关键词： dynamic flowgraph methodology Fault Tree Digital I&C system Reactor Protection System

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dynamic flowgraph modeling of process and control systems of a nuclear-based hydrogen production plant

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2010年第18期35卷 9569-9580页

作者： Al-Dabbagh, Ahmad W. Lu, Lixuan Univ Ontario Inst Technol Fac Energy Syst & Nucl Sci Fac Engn & Appl Sci Oshawa ON L1H 7K4 Canada

Modeling and analysis of system reliability facilitate the identification of areas of potential improvement. The dynamic flowgraph methodology (DFM) is an emerging discrete modeling framework that allows for capturing time dependent behaviour, switching logic and multi-state representation of system components. The objective of this research is to demonstrate the process of dynamic flowgraph modeling of a nuclear-based hydrogen production plant with the copper chlorine (Cu-Cl) cycle. Modeling of the thermochemical process of the Cu-Cl cycle in conjunction with a networked control system proposed for monitoring and control of the process is provided. This forms the basis for future component selection. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

关键词： Process reliability dynamic flowgraph methodology Nuclear-based hydrogen production Copper-chlorine cycle Networked control system

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A BENCHMARK SYSTEM FOR COMPARING RELIABILITY MODELING APPROACHES FOR DIGITAL INSTRUMENTATION AND CONTROL SYSTEMS

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NUCLEAR TECHNOLOGY 2009年第1期165卷 53-95页

作者： Kirschenbaum, Jason Bucci, Paolo Stovsky, Michael Mandelli, Diego Aldemir, Tunc Yau, Michael Guarro, Sergio Ekici, Eylem Arndt, Steven A. Ohio State Univ Nucl Engn Program Scott Lab 427 Columbus OH 43102 USA Ohio State Univ Dept Comp Sci & Engn Dreese Labs 395 Columbus OH 43210 USA Ohio State Univ Dept Elect & Comp Engn Dreese Labs 320 Columbus OH 43210 USA US Nucl Regulatory Commiss Off Nucl Regulatory Res Washington DC 20555 USA

There is an accelerating trend to upgrade and replace nuclear power plant analog instrumentation and control systems with digital systems. While various methodologies are available for the reliability modeling of these systems for plant probabilistic risk assessments, there is no benchmark system that can be used as the basis for methodology comparison. A system representative of the steam generator feedwater control systems in pressurized water reactors is proposed for such a comparison. dynamic reliability modeling of the benchmark system for an example initiating event is illustrated using the Markov/cell-to-cell mapping technique and dynamic flowgraph methodologies.

关键词： Markov dynamic flowgraph methodology dynamic PRA

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Prime implicants in dynamic reliability analysis

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RELIABILITY ENGINEERING & SYSTEM SAFETY 2016年 146卷 39-46页

作者： Tyrvainen, Tero VTT Tech Res Ctr Finland Lifetime Management FI-02044 Espoo Finland

This paper develops an improved definition of a prime implicant for the needs of dynamic reliability analysis. Reliability analyses often aim to identify minimal cut sets or prime implicants, which are minimal conditions that cause an undesired top event, such as a system's failure. dynamic reliability analysis methods take the time-dependent behaviour of a system into account. This means that the state of a component can change in the analysed time frame and prime implicants can include the failure of a component at different time points. There can also be dynamic constraints on a component's behaviour. For example, a component can be non-repairable in the given time frame. If a non-repairable component needs to be failed at a certain time point to cause the top event, we consider that the condition that it is failed at the latest possible time point is minimal, and the condition in which it fails earlier non-minimal. The traditional definition of a prime implicant does not account for this type of time-related minimality. In this paper, a new definition is introduced and illustrated using a dynamic flowgraph methodology model. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Prime implicant dynamic reliability analysis dynamic flowgraph methodology

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Hybrid DFM - Petri net approach for dynamic reliability analysis of smart transmitters

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QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL 2023年第6期39卷 2438-2453页

作者： Garg, Vipul Vinod, Gopika Prasad, Mahendra Santhosh, T. V. Shrestha, N. B. Chattopadhyay, J. Bhabha Atom Res Ctr Reactor Safety Div Mumbai India

Smart transmitters are increasingly being deployed in safety critical systems. Although the processing and diagnostic features provided by digital systems are advantageous, it introduces additional complexity in reliability modelling of systems. The conventional Fault Tree Analysis (FTA) method for system reliability analysis has its shortcomings in modelling digital systems, to incorporate its dynamic system interaction and failure modes in detail. This is because some of the failure modes may arise due to the dynamic interactions between the modules of the system. dynamic flowgraph methodology (DFM) was identified as one of the optimistic approaches to handle these interactions. DFM approach combines multi-valued logic modelling and analysis capabilities to handle systems consisting of components that have multiple degraded states and exhibit dynamic behaviour. However, only few DFM tools have been developed and some of them are not available in public domain. The DFM approach relies heavily on development and implementation of its decision tables. The logic information present within the decision tables can be meticulously implemented using Petri Nets. Also, there are plenty of free Petri Nets tools available online. Thus, the idea of DFM was used in this work to capture the dynamic interactions by developing decision tables. The decision tables were transformed into the Petri Net models to perform the analysis. The paper demonstrates the potential of the hybrid DFM - Petri Net approach for dynamic reliability analysis of smart transmitter.

关键词： Petri Nets dynamic Reliability dynamic flowgraph methodology

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