Research On The TMSDG Methods Of Fault Diagnosis And Fault Risk Assessment For Aircraft

When fault diagnosis is conducted in system of Civil aircraft，especially in the newlydeveloped aircraft，There are many complex faults with multiple coupling influencing factors, andsymptoms. It is difficult to build accurate quantitative models and lack of prior knowledge.Tosolve these problems and conduct effective fault isolation of ircraft multi-condition process thispaper proposed A new qualitative description model—process dynamic signed directed graph(TMSDG) based on SDG which has the ability to accommodate large-scale deep knowledge andhandle complicated cause-effect relationship, Four Problem are studied as below:(1)The definition of TMSDG model is given. TMSDG model is built by combining SDGmodel to the system structure, introducing the stage conditions, unmeasured nodes in SDG.TMSDG not only inherits the characteristics of SDG model but also has the capacity of containinglarge-scale potential information such as structure, test and maintenance. which can support bothautomatic diagnosis and interactive diagnosis.TMSDG can meet the actual needs of change ofoperation conditions. According the characteristics of transmission between hierarchies of failuremodes a hierarchical modeling method which can make modeling easier is studied. the TMSDGmodel has good encapsulation, reusability, so it can support complex system diagnosis and civilaviation maintenance system(2)A hierarchical diagnostic strategy based on TMSDG is studied．First, the specificconditions of failure are determined and the corresponding single-state stable SDG models arereconstructed. Then, possible fault sources are reasoned based on single-state stable SDG modelby introducing the fault-fault dependence matrix, with accessibility theory and the compatibilitycalculation principle. Last,The final diagnosis algorithm integrated multiple modes of thediagnosis. Hierarchical diagnostic strategy avoids the symbols assumption and symbols correctionof unmeasurement nodes, greatly improving the efficiency of diagnosis and diagnosis accuracy.The further reduce redundancy solution, and to improve the diagnostic accuracy.(3)A multi-value AND/OR graph is presented to describe the test sequencing problem ofaircraft system and a diagnosis tree generation algorithm based on maximum unit informationentropy is studied. In the given algorithm,the complicated status association and fault-testdependency of complex system fault are modeled and multi-value AND/OR graph with maximuminformation gain per unit cost of the test is developed considering fault probability and testing cost.The AND/OR graph is a fault diagnosis strategy which can effectively help maintenance man tolocate the fault at lower maintenance costs. The generated diagnostic strategy ensures faultisolation with desired precision at desired maintenance level，which meets the requirements ofcivil aircraft maintenance system．(4)A fault risk assessment algorithm based on gray clustering is proposed．For theidentified failure modes, the deterioration trend are predicted by isolating the event tree and faulttree from TMSDG model. This method improves accuracy of risk valuation since the event treesare regarded as risk evaluation objects. It solves the uncertainties problem and inconsistenciesproblem in traditional FMEA risk assessment. The assessment results includes not only riskpriority of fault mode, but also more practical detailed analysis, which can help to set upmaintenance strategy, improvement measures and enhance the ability of eliminating or control ingthese dangerous in the whole life cycle. Finally, Based on theoretical analysis，an intelligent Fault diagnosis system is developed andan aircraft bleed system is employed as an object to validate the proposed method. The case resultsproves the effectivity and utility of this model.