Research On Availability Analysis Approach For The Display System Of Integrated Modular Avionics System

Aircraft cockpit display system is the main way of displaying aircraft status and flight information,and plays an important role in improving flight quality,ensuring flight reliability and safety,and improving pilot’s driving experience.With the development of science and technology,the highly reliable display system of the integrated modular avionics system with a redundant backup architecture has become a development trend,and it has integrated more and more information,leading to a higher complexity of communication links and logic.The traditional safety and availability analysis methods are insufficient to describe the fault causal relationships in the system,the availability analysis is becoming more and more difficult,and even there are situations where the functional availability cannot be accurately analyzed.Therefore,the development of new theoretical methods and techniques for functional availability analysis of the display system of integrated modular avionics system has significant theoretical and practical value,including avoiding over-design or under-design of the system,verifying whether the system function meets the airworthiness requirements,and providing design basis for aircraft development.This thesis focuses on the display system of the integrated modular avionics system.For the availability analysis of display system function based on the traditional availability analysis methods,there are repeated modeling and calculations,inaccurate evaluations,state space explosion,inconsistency between availability analysis models and system design models,and other limitations.To overcome these limitations,this thesis uses the fault causal relationships to describe the fault propagation between equipments,and carries out researches of the qualitative and quantitative evaluation of static determinate fault causal relationships,fuzzy fault causal relationships,dynamic fault causal relationships,and availability analysis based on system communication and design model.The main innovations are as follows:1.This thesis proposes a safety analysis method based on the fault dependent matrix.This method constructs an availability analysis model based on the fault dependent matrix,designs an algorithm to obtain cut-set,and then obtains the failure mode combinations and availability probability of the system’s function failure.Simulation results verify that the proposed method has less modeling workload and smaller storage space.Furthermore,compared with the traditional fault tree analysis method,it avoids the repeated construction of the fault causal relationships in the display system.2.The thesis constructs an availability analysis process based on the fuzzy fault dependent matrix by combing the fuzzy fault tree analysis and safety analysis method based on the fault dependent matrix.At first,an inaccurate failure rate of the equipment and uncertain fault causal relationships of the system are expressed as fault fuzzy number and fuzzy fault causal rate that obey triangular membership functions.Then,the availability analysis model based on the fuzzy fault dependent matrix is constructed.Finally,the analysis order of the failure modes and analysis results can be obtained from the constructed model.Simulation results show that the constructed process can evaluate the worst-case,the best-case,and the most-possible case of the system function availability,providing more accurate analysis results for designers to improve and perfect the display system.3.The thesis designs an availability analysis process combining analytical and simulation analysis methods.During the analytical process,a dynamic fault tree that is refined into dynamic fault sub-tree and static fault sub-tree is used to construct an analytical model describing the dynamic fault causal relationships in the system firstly.Then the Markov analysis and the binary decision diagram method are used for analysis,and results presented by the two methods are summarized eventually to obtain the availability.During the simulation process,the dynamic fault dependent matrix is constructed to describe the dynamic fault causal relationships of the system functions at first,and then a limited number of Monte Carlo simulations are performed to obtain an approximate quantitative evaluation of the availability.The case study shows that the analytical analysis method can reduce the calculation amount compared with the traditional dynamic fault tree analysis,and provide a more accurate analysis result than the static fault tree analysis.In addition,the proposed method can obtain approximate availability probability of the failure condition which meets the airworthiness requirement whether or not the state space explosion occurs.4.The thesis proposes an availability analysis method based on the Interface Control Document(ICD)of the display system.The ICD file is converted into the Alta Rica(a formal language for availability modeling)model firstly,then the availability attributes and fault causal relationships are added to complete the qualitative and quantitative assessment of system availability.Simulation results show that compared with the remodeling method based on Simfia software and the fault tree analysis method based on Relex software,the proposed method here can reduce the construction work of the availability analysis model and the inconsistent between availability analysis model and system design model.5.The thesis proposes an availability analysis method for the design model based on the display system.For the system design model built using the Enterprise Architecture(EA),which is a system design modeling tool,an availability analysis model is created based on the description rules for availability attributes and fault causal relationships designed in this paper.Then availability analysis is performed by automatically generating the fault dependent matrix from the file exported by the EA.The case study shows that this method can enable safety engineers and system design engineers to share the same model,ensure the consistency between the availability analysis model and the system design model,and facilitate reuse of the availability analysis model when the system changes and iterates,which is closer to the actual engineering application.The part of the expression for fault causal relationships of the proposed method has been applied to the development tools developed by domestic key display systems.