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Fault Tree Analysis Based on Dynamic Uncertain Causality Graph

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Presentation on theme: "Fault Tree Analysis Based on Dynamic Uncertain Causality Graph"— Presentation transcript:

1 Fault Tree Analysis Based on Dynamic Uncertain Causality Graph
Zhenxu Zhou Prof. Qin Zhang Institute of Nuclear and New Energy Technology (INET) Tsinghua University

2 Outline Background Intro to DUCG Methodology Examples
Summary and Conclusion

3 Background-Fault Tree Analysis (FTA)
A deductive method consists of qualitative analysis and quantitative analysis Commonly used tools in PSA Widely applied in nuclear power plants (NPP) space systems chemical plants A fault tree

4 Background-Some Problems in FTA
1. Dependencies and circular loops(CLs) Dependencies are caused by shared components shared utilities among and within FTs CLs are caused by mutual or circular dependencies In NPPs, mainly dependencies of support systems not major concerns not well explored

5 Background-Some Problems in FTA
2. Large scales increase in the exponential order 3. Repeated representations additional calculations 4. Non-deterministic causalities may be uncertain not well addressed

6 Background-Other approaches
Binary Decision Diagram (BDD) Bayesian Network (BN) Petri Net (PN) Dependencies CLs Non-deterministic causalities Efficiency~Order~NP Complete Dependencies CLs Non-deterministic causalities Efficiency~Conditional Probability Tables Dependencies CLs Non-deterministic causalities Efficiency~ State Reachability Graphs

7 Outline Background Intro to DUCG Methodology Examples
Summary and Conclusion

8 repeated representations deterministic causalities
Intro to DUCG Dynamic Uncertain Causality Graph (DUCG) is proposed by Prof. Qin Zhang DUCG can deal with dynamics uncertainties CLs has been applied in NPPs space systems chemical plants medical expert system An example of DUCG Able to analyze FTs and solve the issues: dependency CLs large scales repeated representations deterministic causalities

9 Outline Background Intro to DUCG Methodology Examples
Summary and Conclusion

10 Methodology-Mapping Algorithm
Algorithm 1 mapFaultTreeIntoDUCG 01. for each Event in FaultTree do 02. if Event.Type == Basic || Event.Type == Undeveloped then 03. if flow_add.sourceRef.type !=B do 04. currentDUCG.addNode(new XVariable(name=Event.name, probability=Event.probability)) 05. elseif Event.Type == Intermediate || Event.Type == Top then 06. currentDUCG.addNode(new XVariable(name=Event.name, probability= Event.probability)) 07. elseif Event.Type == House then 08. currentDUCG.change(Event.Logic,Event.UpperLogic) 09. endfor 10. for each LogicGate in FaultTree do 11. currentDUCG.addGate(LogicGate.Type, LogicGate.In, LogicGate.Out ) 12. endfor

11 Methodology-Event Mapping
FT DUCG No direct mapping relation.

12 Methodology-Numerical Mapping
House events: commonly used to control whether some special events happen or not have a fixed probability of 0 or 1, expected to occur have direct effects on its logic gates

13 Methodology-Logic Mapping
OR Gate AND Gate 2/3 Gate NOT Gate

14 Methodology-Modelling Improvements
Break Circular Loops (CLs) Assumption 4 in DUCG: Any state of a variable cannot be the cause of any state of the same variable at the same time. A fault tree with CL

15 Methodology-Modelling Improvements
Common Cause Failures (CCF) Represent CCF Gates Adding a NOT Gate (the output of given CCF Gate as its input) to the input of TE Modifying the corresponding P variable with parameter LCCF CCF AND Gate

16 Methodology-Modelling Improvements
Multi-state Events Use M-DUCG instead Statistically Dependencies Are removed because of logic operations before numerical calculations Non-deterministic Causalities Specify the probabilities with Pn;i or Fn;i

17 Methodology-Analysis Improvements
Importance Analysis Extend importance measures to entire system.

18 Methodology-Analysis Improvements
Failure Prediction Fault Diagnosis

19 Outline Background Intro to DUCG Methodology Examples
Summary and Conclusion

20 Example 1 How? If we replace house event B1 with a basic event:
If B10 occurs and B21 doesn’t occur, X61 won’t occur. Corresponding logic gate will be removed which leading to X61 = B51. House event with AND-AND Gate How? Use Z-type variable and modifying LGSs accordingly.

21 Example 2 A feed-control system
Disjoint Sum of Products A feed-control system The importance measurements of each basic events

22 Outline Background Intro to DUCG Methodology Examples
Summary and Conclusion

23 Summary and Conclusion
Compared to classical FTA when dependencies/CLs exist, the results are exact involves uncertainties extends to multi-state variables handles CCF shows how to conduct importance analysis base of online fault diagnosis and failure prediction

24 Thank you for your attention!


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