Quantitative evaluation of Pandora Temporal Fault Trees via Petri Nets

© 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Using classical combinatorial fault trees, analysts are able to assess the effects of combinations of failures on system behaviour but are unable to capture sequence dependent dynamic behaviour. Pandora introduces temporal gates and temporal laws to fault trees to allow sequence-dependent dynamic analysis of events. Pandora can be easily integrated in model-based design and analysis techniques; however, the combinatorial quantification techniques used to solve classical fault trees cannot be applied to temporal fault trees. Temporal fault trees capture state and therefore require a state space solution for quantification of probability. In this paper, we identify Petri Nets as a possible framework for quantifying temporal trees. We describe how Pandora fault trees can be mapped to Petri Nets for dynamic dependability analysis and demonstrate the process on a fault tolerant fuel distribution system model

Rich Interfaces for Dependability: Compositional Methods for Dynamic Fault Trees and Arcade models

This paper discusses two behavioural interfaces for reliability analysis: dynamic fault trees, which model the system reliability in terms of the reliability of its components and Arcade, which models the system reliability at an architectural level. For both formalisms, the reliability is analyzed by transforming the DFT or Arcade model to a set of input-output Markov Chains. By using compositional aggregation techniques based on weak bisimilarity, significant reductions in the state space can be obtained

DFTCalc: a tool for efficient fault tree analysis

Effective risk management is a key to ensure that our nuclear power plants, medical equipment, and power grids are dependable; and it 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 powerful analysis techniques, including aggressive compression techniques to keep the underlying state space small

Systematic approach furthering confirmation measures of safety critical automotive systems

Different system elements are developed independently from diverse suppliers and teams before being integrated together into safety critical automotive systems such as steering or braking systems by a manufacturer. It must be guaranteed that, despite this independent development, the achievement of the safety requirements for the overall system can be demonstrated. The necessary agreements and the integration of the necessary safety information for the overall system generate higher extra costs. In order to reduce development time and cost, systematic reuse can be a solution to engineering the required artifacts. Reassessment represents an additional source of cost. Even small modifications of a system or exchanging a component after it has been certified necessitates a reassessment. The effort required for reassessment, in many cases reaches the original effort of certification for the complete system or even exceeds it. To minimize the effort and cost of a reassessment, this paper introduces a theoretical foundation of a model-based engineering approach to reuse a safety case and change only the modified parts. This paper presents a reusability framework to support the distributed development environment together with the different composition scenarios with respect to ISO26262. A further benefit of this approach is that for development of variants in product-line, the Safety assessment process can now be easily expressed and managed

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

Integrating satisfiability solving in the assessment of system reliability modeled by dynamic fault trees

International audienceFault trees (FTs) and their extensions are diagrammatic formalisms that are commonly used for reliability assessment and that represent the structure function of systems. The structure function determines tie sets and cut sets, and minimal tie sets are instrumental for assessing systems reliability. In a previous paper, we used satisfiability (SAT) techniques to compute tie sets from the structure function. In this paper we define minimal tie sets with sequences (MTSSs) as an extension of minimal tie sets for analyzing dynamic fault trees (DFTs), and we extend our previous techniques for computing MTSSs. We illustrate our approach using a standard case study and assess its performance over several industrial-size benchmarks

Efficient Modelling and Generation of Markov Automata (extended version)

This paper introduces a framework for the efficient modelling and generation of Markov automata. It consists of (1) the data-rich process-algebraic language MAPA, allowing concise modelling of systems with nondeterminism, probability and Markovian timing; (2) a restricted form of the language, the MLPPE, enabling easy state space generation and parallel composition; and (3) several syntactic reduction techniques on the MLPPE format, for generating equivalent but smaller models. Technically, the framework relies on an encoding of MAPA into the existing prCRL language for probabilistic automata. First, we identify a class of transformations on prCRL that can be lifted to the Markovian realm using our encoding. Then, we employ this result to reuse prCRL's linearisation procedure to transform any MAPA specification to an equivalent MLPPE, and to lift three prCRL reduction techniques to MAPA. Additionally, we define two novel reduction techniques for MLPPEs. All our techniques treat data as well as Markovian and interactive behaviour in a fully symbolic manner, working on specifications instead of models and thus reducing state spaces prior to their construction. The framework has been implemented in our tool SCOOP, and a case study on polling systems and mutual exclusion protocols shows its practical applicability

A Methodology for Hierarchical Reliability Analysis of Combat Systems Using FTA and BBN

전투 시스템의 취약점을 분석하여 신뢰성을 높이기 위한 많은 연구가 있다. 전투 시스템의 신뢰성을 분석하기 위해서는 전투 시스템에 대한 다양한 위협 요인을 고려하여야 한다. 대부분의 전투 시스템 신뢰성 분석은 충돌에 관련된 위협을 토대로 신뢰성을 분석하였다. 하지만 충돌과 더불어 에너지, 충격, 진동 등의 다양한 위협이 존재한다. 최근 에너지, 충격, 진동 등의 각각의 위협에 대한 연구와 더불어 이러한 위협들을 동시에 고려해야할 필요성이 대두되었다. 하지만 다양한 위협을 동시에 고려하는 것에 대한 직접적인 방법은 연구되지 않았다. 이에 전투시스템의 신뢰성 분석을 위하여 충돌뿐만 아니라 에너지, 충격, 진동 등 다양한 위협을 동시에 고려하는 방법이 필요하다. 또한, 구성 요소간의 의존적인 관계를 모두 표현할 수 있는 분석 기법을 이용하여 전투 시스템의 신뢰성을 분석하여야 한다. 본 논문에서는 각 요소의 특징들에 따라 FTA 기법과 BBN을 사용하여 계층적으로 신뢰성을 분석하는 방법을 제안한다. 제안하는 방법은 2개의 계층으로 구성되어 있다. 하위 계층에서는 FTA 기법을 이용하여 전투 시스템의 각 구성 요소의 고장 확률을 도출한다. 구성 요소의 고장 확률은 구성 요소가 가질 수 있는 다양한 위협을 동시에 고려하여 분석된다. 상위 계층에서는 하위 계층에서 도출된 구성 요소의 고장 확률을 기반으로 기능 수준(function-level)의 상실 확률을 분석하여 전투 시스템의 신뢰성을 분석한다. 이때 구성 요소들의 고장에 대한 종속적 관계를 고려하기 위하여 BBN을 이용한다. 이러한 방법의 효용성을 검증하기 위하여 대상 시스템을 정의하고 제안하는 방법을 이용하여 사례 연구를 진행한다. 사례 연구에서는 제안하는 분석 방법에 대한 계산을 자동화하기 위해 개발한 프로그램을 이용한다. |There are many studies to analyze the vulnerability of combat system to improve reliability. To analyze the reliability of a combat system, various threats affecting the combat system should be considered. Most reliability analysis of the combat system analyzed reliability based on impact-related threats. However, there are various threats such as energy, shock, and vibration as well as impact. Recently, it is necessary to simultaneously consider the threats, in addition to studying various threats such as fire, shock, and energy. However, no method of integrating the threats has been studied. In order to analyze the reliability of the combat system, it is necessary to take an integrated approach to energy, shock, vibration, and impact. In addition, the reliability of the combat system should be analyzed using reliability techniques that can express all of the dependency relationships between components. In this paper, we propose a method to analyze reliability using FTA and BBN hierarchically according to the features of each element. This method consists of two layers: a lower layer and a upper layer. In the lower layer, the failure probability of each component of the combat system is analyzed using the FTA. The failure probability of a component is analyzed considering the possible threats of the component. In the upper layer, the loss probability of function-level is analyzed based on the failure probability of the components derived from the lower layer. And the reliability of combat system is analyzed using loss probability of function. BBN is used to consider the dependence of the failure of components. To verify utility of the proposed method, we defines the target system and analyzes reliability of the system through the case study. we uses a program developed to automate the calculation of the proposed analysis method.제 1 장 서 론 1 제 2 장 관련 연구 4 2.1 FTA 기법 4 2.2 BBN 8 2.3 FTA 기법과 BBN의 비교 11 제 3 장 FTA와 BBN을 이용한 전투 시스템의 계층적 신뢰성 분석 13 3.1 계층적 신뢰성 분석 방법 13 3.2 하위 계층 : 구성 요소별 고장 확률 분석 16 3.3 상위 계층 : 기능 수준의 상실 확률 분석 18 제 4 장 사례 연구 27 4.1 분석 대상 27 4.2 신뢰성 분석 30 제 5 장 결 론 44 참고문헌 45Maste

Method for evaluating an extended fault tree to analyse the dependability of complex systems: application to a satellite-based railway system

Evaluating dependability of complex systems requires the evolution of the system states over time to be analysed. The problem is to develop modelling approaches that take adequately the evolution of the different operating and failed states of the system components into account. The Fault Tree (FT) is a well- known method that efficiently analyse the failure causes of a system and serves for reliability and availability evaluations. As FT is not adapted to dynamic systems with repairable multi-state compo- nents, extensions of FT (eFT) have been developed. However efficient quantitative evaluation processes of eFT are missing. Petri nets have the advantage of allowing such evaluation but their construction is difficult to manage and their simulation performances are unsatisfactory. Therefore, we propose in this paper a new powerful process to analyse quantitatively eFT. This is based on the use of PN method, which relies on the failed states highlighted by the eFT, combined with a new analytical modelling approach for critical events that depend on time duration. The performances of the new process are demonstrated through a theoretical example of eFT and the practical use of the method is shown on a satellite-based railway system