A Nested Petri Net – Fault Tree Approach for System Dependency Modelling

The Dynamic and Dependent Tree Theory (D²T²) provides a safety analysis framework able to model complex features of engineering systems, such as dynamic behaviour, complex maintenance strategies or components dependencies which cannot be represented in traditional Fault Tree methods. This is achieved through the tailored integration of flexible modelling techniques, such as Petri Nets and Markov Models, within the Fault Tree framework: differently from similar approaches (e.g., Dynamic Fault Trees), the D²T² methodology does not impose any restriction on the location or type of dependencies. However, when these involve multiple components, such as in the case of redundant trains, the resulting Petri Nets or Markov Models can become rapidly large and convoluted, putting strain on the analyst. This work proposes a generalization of the D²T² methodology based on the nesting of Petri Nets and Fault Trees models: the use of the first is extended to represent dynamic or complex relationship involving entire sets of components (e.g., trains or subsystems represented by section of the main Fault Tree) rather then merely individual ones, dramatically reducing the complexity of the user-defined models. A simple case study is proposed to demonstrate the approach, and the results obtained investigated throughout together with the potential for automatic generation of the dependency models.

Keywords: Fault trees, Safety analysis, Component dependency, Degradation, Markov models, Petri nets.

Download PDF