Modeling of function failure propagation across uncoupled systems

The design of modern complex engineered systems must rapidly and accurately be developed to satisfy customer needs while accomplishing required functions with a minimum number of failures. Failure analysis in the conceptual stage of design, including the propagation of failures, has expanded in recent years to account for failures in functional modeling. However, function failure propagation across uncoupled functions and subsystems has not been fully addressed; failures are known to cross these boundaries in complex systems. To address this research gap, a functional model based geometric method of predicting and mitigating functional failure propagation across systems, which are uncoupled during nominal use cases, is presented. Geometric relationships including function location and physical properties are established between uncoupled functions to serve as failure propagation flow paths. Mitigation options are developed based upon the geometric relationships and a path toward physical functional layout is provided to limit failure propagation across uncoupled subsystems. The model-based geometric method of predicting and mitigating functional failure propagation across uncoupled engineered systems guides designers toward improved protection and isolation of cross-subsystem failure propagation. The proposed method is validated using the case study of a pressurized water nuclear reactor modeled using APROS, a first principal simulator. Results identified that the top 10 failures exceeded those of PRA in importance based on the probability of failure.