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  • 1
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    Multiple Fault Isolation in Redundant Systems (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: We consider the problem of sequencing tests to isolate multiple faults in redundant (fault-tolerant) systems with minimum expected testing cost (time). It can be shown that single faults and minimal faults, i.e., minimum number of failures with a failure signature different from the union of failure signatures of individual failures, together with their failure signatures, constitute the necessary information for fault diagnosis in redundant systems. In this paper, we develop an algorithm to find all the minimal faults and their failure signatures. Then, we extend the Sure diagnostic strategies [1] of our previous work to diagnose multiple faults in redundant systems. The proposed algorithms and strategies are illustrated using several examples.
    Keywords: Quality Assurance and Reliability
    Type: Multiple Fault Isolation in Redundant Systems; NASA/CR-97-205940
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  • 2
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    Sequential Testing Algorithms for Multiple Fault Diagnosis (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: In this paper, we consider the problem of constructing optimal and near-optimal test sequencing algorithms for multiple fault diagnosis. The computational complexity of solving the optimal multiple-fault isolation problem is super-exponential, that is, it is much more difficult than the single-fault isolation problem, which, by itself, is NP-hard. By employing concepts from information theory and AND/OR graph search, we present several test sequencing algorithms for the multiple fault isolation problem. These algorithms provide a trade-off between the degree of suboptimality and computational complexity. Furthermore, we present novel diagnostic strategies that generate a diagnostic directed graph (digraph), instead of a diagnostic tree, for multiple fault diagnosis. Using this approach, the storage complexity of the overall diagnostic strategy reduces substantially. The algorithms developed herein have been successfully applied to several real-world systems. Computational results indicate that the size of a multiple fault strategy is strictly related to the structure of the system.
    Keywords: Quality Assurance and Reliability
    Type: Multiple Fault Isolation in Redundant Systems; NASA/CR-97-205940
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  • 3
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    Algorithms for Multiple Fault Diagnosis With Unreliable Tests (1997)
    In:  CASI
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    Publication Date: 2004-12-03
    Description: In this paper, we consider the problem of constructing optimal and near-optimal multiple fault diagnosis (MFD) in bipartite systems with unreliable (imperfect) tests. It is known that exact computation of conditional probabilities for multiple fault diagnosis is NP-hard. The novel feature of our diagnostic algorithms is the use of Lagrangian relaxation and subgradient optimization methods to provide: (1) near optimal solutions for the MFD problem, and (2) upper bounds for an optimal branch-and-bound algorithm. The proposed method is illustrated using several examples. Computational results indicate that: (1) our algorithm has superior computational performance to the existing algorithms (approximately three orders of magnitude improvement), (2) the near optimal algorithm generates the most likely candidates with a very high accuracy, and (3) our algorithm can find the most likely candidates in systems with as many as 1000 faults.
    Keywords: Quality Assurance and Reliability
    Type: Multiple Fault Isolation in Redundant Systems; NASA/CR-97-205940
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  • 4
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    Sequential Test Strategies for Multiple Fault Isolation (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: In this paper, we consider the problem of constructing near optimal test sequencing algorithms for diagnosing multiple faults in redundant (fault-tolerant) systems. The computational complexity of solving the optimal multiple-fault isolation problem is super-exponential, that is, it is much more difficult than the single-fault isolation problem, which, by itself, is NP-hard. By employing concepts from information theory and Lagrangian relaxation, we present several static and dynamic (on-line or interactive) test sequencing algorithms for the multiple fault isolation problem that provide a trade-off between the degree of suboptimality and computational complexity. Furthermore, we present novel diagnostic strategies that generate a static diagnostic directed graph (digraph), instead of a static diagnostic tree, for multiple fault diagnosis. Using this approach, the storage complexity of the overall diagnostic strategy reduces substantially. Computational results based on real-world systems indicate that the size of a static multiple fault strategy is strictly related to the structure of the system, and that the use of an on-line multiple fault strategy can diagnose faults in systems with as many as 10,000 failure sources.
    Keywords: Quality Assurance and Reliability
    Type: Multiple Fault Isolation in Redundant Systems; NASA/CR-97-205940
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  • 5
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    Multiple Fault Isolation in Redundant Systems (1997)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Fault diagnosis in large-scale systems that are products of modern technology present formidable challenges to manufacturers and users. This is due to large number of failure sources in such systems and the need to quickly isolate and rectify failures with minimal down time. In addition, for fault-tolerant systems and systems with infrequent opportunity for maintenance (e.g., Hubble telescope, space station), the assumption of at most a single fault in the system is unrealistic. In this project, we have developed novel block and sequential diagnostic strategies to isolate multiple faults in the shortest possible time without making the unrealistic single fault assumption.
    Keywords: Quality Assurance and Reliability
    Type: NASA/CR-97-205940 , NAS 1.26:205940 , Multiple Fault Isolation in Redundant Systems
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  • 6
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    A quantitative analysis of the F18 flight control system (1993)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper presents an informal quantitative analysis of the F18 flight control system (FCS). The analysis technique combines a coverage model with a fault tree model. To demonstrate the method's extensive capabilities, we replace the fault tree with a digraph model of the F18 FCS, the only model available to us. The substitution shows that while digraphs have primarily been used for qualitative analysis, they can also be used for quantitative analysis. Based on our assumptions and the particular failure rates assigned to the F18 FCS components, we show that coverage does have a significant effect on the system's reliability and thus it is important to include coverage in the reliability analysis.
    Keywords: AIRCRAFT INSTRUMENTATION
    Type: AIAA PAPER 93-4574 , In: AIAA Computing in Aerospace Conference, 9th, San Diego, CA, Oct. 19-21, 1993, Technical Papers. Pt. 1 (A94-11401 01-62); p. 668-675.
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  • 7
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    Characterization of Model-Based Reasoning Strategies for Use in IVHM Architectures (2003)
    In:  CASI
    Details
    Publication Date: 2018-06-06
    Description: Open architectures are gaining popularity for Integrated Vehicle Health Management (IVHM) applications due to the diversity of subsystem health monitoring strategies in use and the need to integrate a variety of techniques at the system health management level. The basic concept of an open architecture suggests that whatever monitoring or reasoning strategy a subsystem wishes to deploy, the system architecture will support the needs of that subsystem and will be capable of transmitting subsystem health status across subsystem boundaries and up to the system level for system-wide fault identification and diagnosis. There is a need to understand the capabilities of various reasoning engines and how they, coupled with intelligent monitoring techniques, can support fault detection and system level fault management. Researchers in IVHM at NASA Ames Research Center are supporting the development of an IVHM system for liquefying-fuel hybrid rockets. In the initial stage of this project, a few readily available reasoning engines were studied to assess candidate technologies for application in next generation launch systems. Three tools representing the spectrum of model-based reasoning approaches, from a quantitative simulation based approach to a graph-based fault propagation technique, were applied to model the behavior of the Hybrid Combustion Facility testbed at Ames. This paper summarizes the characterization of the modeling process for each of the techniques.
    Keywords: Computer Programming and Software
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  • 8
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    Stage Separation Failure: Model Based Diagnostics and Prognostics (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Safety of the next-generation space flight vehicles requires development of an in-flight Failure Detection and Prognostic (FD&P) system. Development of such system is challenging task that involves analysis of many hard hitting engineering problems across the board. In this paper we report progress in the development of FD&P for the re-contact fault between upper stage nozzle and the inter-stage caused by the first stage and upper stage separation failure. A high-fidelity models and analytical estimations are applied to analyze the following sequence of events: (i) structural dynamics of the nozzle extension during the impact; (ii) structural stability of the deformed nozzle in the presence of the pressure and temperature loads induced by the hot gas flow during engine start up; and (iii) the fault induced thrust changes in the steady burning regime. The diagnostic is based on the measurements of the impact torque. The prognostic is based on the analysis of the correlation between the actuator signal and fault-induced changes in the nozzle structural stability and thrust.
    Keywords: Spacecraft Design, Testing and Performance
    Type: ARC-E-DAA-TN1719 , Annual Conference of the Prognostics and Health Management Society, 2010 (PHM 2010); Oct 10, 2010 - Oct 14, 2010; Portland, OR; United States
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  • 9
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    Modeling and Diagnostic Software for Liquefying-Fuel Rockets (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A report presents a study of five modeling and diagnostic computer programs considered for use in an integrated vehicle health management (IVHM) system during testing of liquefying-fuel hybrid rocket engines in the Hybrid Combustion Facility (HCF) at NASA Ames Research Center. Three of the programs -- TEAMS, L2, and RODON -- are model-based reasoning (or diagnostic) programs. The other two programs -- ICS and IMS -- do not attempt to isolate the causes of failures but can be used for detecting faults. In the study, qualitative models (in TEAMS and L2) and quantitative models (in RODON) having varying scope and completeness were created. Each of the models captured the structure and behavior of the HCF as a physical system. It was noted that in the cases of the qualitative models, the temporal aspects of the behavior of the HCF and the abstraction of sensor data are handled outside of the models, and it is necessary to develop additional code for this purpose. A need for additional code was also noted in the case of the quantitative model, though the amount of development effort needed was found to be less than that for the qualitative models.
    Keywords: Computer Programming and Software
    Type: ARC-15341-1 , NASA Tech Briefs, June 2005; 32
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  • 10
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    Using Auto-Generated Diagnostic Trees to Support Test Procedures (2011)
    In:  Other Sources
    Details
    Publication Date: 2019-08-13
    Description: No abstract available
    Keywords: Quality Assurance and Reliability
    Type: NASA OSMA SARP Technical Interchange Meeting; Aug 04, 2011 - Aug 10, 2011; Washington, D.C.; United States
    Format: text
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