Reliability analysis of dynamic systems by translating temporal fault trees into Bayesian networks

Classical combinatorial fault trees can be used to assess combinations of failures but are unable to capture sequences of faults, which are important in complex dynamic systems. A number of proposed techniques extend fault tree analysis for dynamic systems. One of such technique, Pandora, introduces temporal gates to capture the sequencing of events and allows qualitative analysis of temporal fault trees. Pandora can be easily integrated in model-based design and analysis techniques. It is, therefore, useful to explore the possible avenues for quantitative analysis of Pandora temporal fault trees, and we identify Bayesian Networks as a possible framework for such analysis. We describe how Pandora fault trees can be translated to Bayesian Networks for dynamic dependability analysis and demonstrate the process on a simplified fuel system model. The conversion facilitates predictive reliability analysis of Pandora fault trees, but also opens the way for post-hoc diagnostic analysis of failures

Fault Tree Analysis: a survey of the state-of-the-art in modeling, analysis and tools

Fault tree analysis (FTA) is a very prominent method to analyze the risks related to safety and economically critical assets, like power plants, airplanes, data centers and web shops. FTA methods comprise of a wide variety of modelling and analysis techniques, supported by a wide range of software tools. This paper surveys over 150 papers on fault tree analysis, providing an in-depth overview of the state-of-the-art in FTA. Concretely, we review standard fault trees, as well as extensions such as dynamic FT, repairable FT, and extended FT. For these models, we review both qualitative analysis methods, like cut sets and common cause failures, and quantitative techniques, including a wide variety of stochastic methods to compute failure probabilities. Numerous examples illustrate the various approaches, and tables present a quick overview of results

EEMCS final report for the causal modeling for air transport safety (CATS) project

This document reports on the work realized by the DIAM in relation to the completion of the CATS model as presented in Figure 1.6 and tries to explain some of the steps taken for its completion. The project spans over a period of time of three years. Intermediate reports have been presented throughout the project’s progress. These are presented in Appendix 1. In this report the continuous‐discrete distribution‐free BBNs are briefly discussed. The human reliability models developed for dealing with dependence in the model variables are described and the software application UniNet is presente

ASTRA Plus User Manual

This report describes the user interface and the main commands to perform system dependability analysis by means of ASTRA Plus. This package implements the analysis methods developed at the Institute for the Protection and Security of the Citizen from mid-2008. ASTRA Plus is composed of the Fault Tree Analysis (FTA) module and of the Concurrent Importance and Sensitivity Analysis (CISA) module. The FTA module contains three different methods for solving a fault tree; all are based on the state of the art approach of Binary Decision Diagrams (BDD). These three methods allow the user to analyse fault trees of increasing complexity (i.e. increasing number of basic events and gates). In particular the third method, which is based on functional decomposition, allow performing the analysis of fault trees of very high complexity. The CISA module is based on a new methodology for system design improvement. The key operation is the calculation of Global Importance Measures of basic events considering all system fault trees. This allows identifying the weakest part of the system with reference to all top-events. Then the on-line sensitivity analysis allows the user to rapidly identify the set of suitable design improvements from which the best cost-effective one can be selected.JRC.G.6-Security technology assessmen

DFTCalc: a tool for efficient fault tree analysis (extended version)

Effective risk management is a key to ensure that our nuclear power plants, medical equipment, and power grids are dependable; and is often required by law. Fault Tree Analysis (FTA) is a widely used methodology here, computing important dependability measures like system reliability. This paper presents DFTCalc, a powerful tool for FTA, providing (1) efficient fault tree modelling via compact representations; (2) effective analysis, allowing a wide range of dependability properties to be analysed (3) efficient analysis, via state-of-the-art stochastic techniques; and (4) a flexible and extensible framework, where gates can easily be changed or added. Technically, DFTCalc is realised via stochastic model checking, an innovative technique offering a wide plethora of pow- erful analysis techniques, including aggressive compression techniques to keep the underlying state space small

ASTRA 3.x: Theoretical Manual

This report describes the main algorithms implemented in ASTRA 3.x to analyse coherent and non-coherent fault trees. ASTRA 3.x is fully based on the state-of-the-art of Binary Decision Diagrams (BDD) approach. In case of non-coherent fault trees ASTRA 3.x dynamically assigns to each node of the graph a label that identifies the type of the associated variable in order to drive the application of the most suitable analysis algorithms. The resulting BDD is referred to as Labelled BDD (LBDD). Exact values of the unavailability, expected number of failure and repair are calculated; the unreliability upper bound is automatically determined under given conditions. Several importance measures of basic events are also provided. From the LBDD a ZBDD embedding all MCS is obtained from which a subset of Significant Minimal Cut Sets (SMCS) is determined through the application of the cut-off techniques. An important issue is related to the analysis of safety related systems according to the IEC 61508 international standard. In order to simplify the fault tree modelling and analysis a new component type has been defined allowing determining, for any configuration, the PFDavg and PFHavg values. The Staggered testing policy is also applicable besides the Sequential testing implicitly considered by the IEC standardJRC.G.6-Security technology assessmen