Fault Tree Ring-Closure Handling in Failure Propagation Models
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Solution Overview
Problem
Existing safety-critical systems face challenges in handling loops within failure propagation models that use Boolean logic, as these models cannot contain loops, leading to issues in identifying and mitigating ring closures, which are problematic in complex systems with multi-dimensional loops and multiple entry/exit points.
Innovation Solution
A computer-implemented method for modeling multi-component control or actuator systems using a fault tree, where failure propagation paths are back-traced to identify and replace ring closures with predefined expressions, allowing for the handling of complex loops and improving safety assurance in safety-critical systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If loops are removed from failure propagation models to maintain Boolean logic validity, then the models become computationally manageable, but the ability to accurately represent complex systems with multi-dimensional loops is lost
Solution Approach 1:
The patent segments the failure propagation model into multiple evaluation passes, where each pass handles a subset of the system's loops. By dividing the complex system into manageable segments that can be evaluated separately, the method maintains Boolean logic validity while preserving the representation of multi-dimensional loops across multiple evaluation stages.
Solution Approach 2:
The patent implements periodic action through multiple evaluation passes over the fault tree. Instead of a single evaluation, the system periodically re-evaluates the fault tree with updated loop handling, allowing accurate representation of complex loops while maintaining computational manageability through iterative refinement.
2Reliability
If ring closures are detected and handled in fault trees, then safety assurance is improved, but computational cost increases
Solution Approach 1:
The patent applies preliminary action by detecting ring closures before they propagate through the entire fault tree evaluation. By identifying and handling ring closures in advance during the evaluation process, the method improves safety assurance while limiting computational effort to only the necessary portions of the fault tree.
Solution Approach 2:
The patent extracts ring closures from the fault tree evaluation process by identifying them as separate entities that can be handled independently. This extraction allows the main fault tree evaluation to proceed efficiently while ring closures are processed separately, improving safety assurance without proportionally increasing overall computational effort.
3Productivity
If automatic composition of failure propagation models is used, then system integration is accelerated, but loops cannot be prevented during composition
Solution Approach 1:
The patent applies inversion by reversing the traditional approach: instead of trying to prevent loops during automatic composition, it allows loops to form naturally during rapid system integration and then handles them through multiple evaluation passes. This inversion maintains high productivity during composition while managing loop complexity in the evaluation phase.
Solution Approach 2:
The patent implements dynamics by making the failure propagation model adaptive to loops that emerge during automatic composition. The model dynamically adjusts through multiple evaluation passes, handling the complexity of generated loops while maintaining the productivity benefits of automatic system integration.
Data Source
AI summary
Modeling a multi-component control or actuator system using a fault tree is provided, which solves the problem of ring closures included in a fault tree. To identify ring closures, failure propagation paths are back-traced and is checked if the respective failure propagation path forms a ring closure.