Resilient system design for Prognosis and Health Monitoring of an ocean power generator

In this paper we introduce a new methodology that integrates system resilience engineering and hazard analysis into complex system design. We then demonstrate its performance by applying it to the design of a Prognosis and Health Monitoring (PHM) system for an ocean current power generator. Three common methodologies for system hazard analysis were tested by applying them to the PHM system´s network topology architecture; STAMP-based Process Analysis (STPA), Hazard and Operability Analysis (HAZOP), and a Resilience Engineering, Heuristic-based approach. While all three approaches adequately revealed most PHM system hazards, which assisted in identifying the means with which to mitigate them, none of the approaches fully addressed the multi-state dimensionality of the sub-components of the system, missing risky and hazardous scenarios. We developed the System Hazard Indication and Extraction Learning Diagnosis (SHIELD) methodology for system hazard analysis and resilient design. SHIELD integrates state space analysis into the hazard analysis process in order to facilitate the location of undiscovered hazard scenarios. Our approach uses recursive, top-down system decomposition with subsystem, interface, and process cycle identification. Then, a bottom-up recursive evaluation is completed where we analyze the subsystem state space and state transitions with regard to hazards/failures in process cycles. This yields a comprehensive list of failure states and scenarios. Finally, a top-down prioritized application of resilient engineering heuristics which address hazard scenarios is prescribed. This final phase results in a comprehensive, complete analysis of complex system architectures forcing resilience into the final system design.