Dynamic flowgraph methodology and its applications

Dynamic flowgraph methodology (DFM) is method for the reliability analysis of dynamic systems with time-dependencies and feedback loops. As in fault tree analysis, the aim of DFM is to identify which conditions can cause a top event, which can be, for example, the system's failure. DFM has been most often applied to different digital control systems. One reason for this is that a DFM model can represent the interactions between a control system and the controlled process. Components of DFM models are analysed at discrete time points and they can have multiple states. The reason for the development of DFM is that traditional methods, such as fault tree analysis, can describe the system's dynamic behaviour only in a limited manner. DFM can more accurately represent system's evolution in time. This report gives an overview of the DFM method and presents the applications of DFM that are found in literature. The application areas include digital control and safety systems in nuclear power plants, space systems, hydrogen production plants, human performance, networked control systems and field programmable gate arrays. In most of the applications, DFM has been used to analyse how control system failures can cause some physical variable, e.g. water level or pressure, to have too low or high value. Generally, DFM has been found useful within the application areas. Most of the presented models have been quite moderately sized, though larger models exist too.