Safety And Reliability Analysis For The Doors Of Civil Aircraft

Increasingly,modernized civil aircraft becomes a popular way for passages and goods transportation due to its high speed and payload.Among the most significant criterions of civil aircraft,i.e.,safety,economy and amenity,safety is the priority that should be considered preliminary.The safety of the cabin door,as one of the most critical components on the aircraft,has been required by the airworthiness provisions.This dissertation conducts a series of the correlated research and analysis on the safety and reliability of civil aircraft door systems,where the specific steps and processes of safety analysis are established.Furthermore,the locking reliability of typical locking mechanism on civil aircrafts is studied in view of the over-center locking principle.Eventually,two improved cuckoo search algorithms with a specific aim for structural reliability are proposed.The main contents and innovations of this thesis are six-fold:1.The basic theories of safety analysis methods of civil aircraft cabin door systems are listed,including Functional Hazardous Analysis(FHA),Failure Mode and Effects Analysis(FMEA),Fault Tree Analysis(FTA)and Common Cause Analysis(CCA),where the logical relationship between the aforementioned methods is proposed.Additionally,the reliability analysis models and methods which are involved with the bottom events of the main failure modes are proposed.Then,based on the above safety analysis methods and combined with guidance files of SAE ARP4761,the specific steps of the cabin doors safety analysis are developed.2.The preliminary safety analysis is addressed using a forward cargo door as a test bed.Firstly,three main failure modes of the cargo door,viz.“inadvertent opening”,“opening prevented” and “erroneous indication of indication system”,which are obtained by the FHA.Secondly,failures at level I and II are observed by FMEA,and those failures provide the bottom events for further FTA.Thirdly,the main failure modes are qualitatively analyzed by FTA,and the reliability modeling and analysis methods of the bottom events in fault trees are proposed.Finally,minimum cut sets of each fault tree and the solving methods of failure probability of top events are established.The research work in this part forms the main safety and reliability qualitative analysis methods,and can solve the qualitative safety analysis problem of the doors of civil aircraft.3.A comprehensive investigation is addressed on the principle of “over-center locking” mechanisms,where a reliability analytical model is developed accordingly.By isolating the wear performances of hinge joint and bearings,a wear model of self-lubricating rod end bearing is proposed.In addition,the over-center locking reliability under the influence of initial gap and wear according to the "effective lever length theory" and "continuous contact model" is identified.An engineering application is used to illustrate the feasibility and rationality of the proposed method.The research work in this part can principally provide guidance on the design,production and usage of the over-center locking-based mechanism.4.To overcome the complexity and inefficiency in the process of reliability analysis on spatial mechanism's over-center locking,this thesis combines the genetic algorithm and Newton method for the sake of solving the optimization problem which is transformed from the nonlinear equations of over-center angle.In order to accurately obtain the variance of the over-center locking angle in a short computational time,the nonlinear equations are replaced by the well-trained neural networks using the outstanding nonlinear mapping ability of artificial neural networks.The efficiency and accuracy of the proposed method is demonstrated via an engineering application.Further attentions have been contributed on the influence of the neural network's main parameters on the failure probabilities of the spatial mechanism.Results derived the recommended values of the main parameters are obtained.The outcomes of this part can provide guidance to the reliability analysis of civil aircraft mechanisms utilizing the spatial mechanism to lock.5.One of the swarm intelligence optimization algorithms named the cuckoo search algorithm is studied,and the improved forms of the algorithm are utilized in the reliability analysis of the structure and mechanism of cabin doors.The significant parameters which affect the global search and local search capabilities in the cuckoo search algorithm are tuned properly in different ways.Meanwhile,the search equation in the algorithm has been modified to enhance its local search ability.The improved cuckoo search algorithms combined with artificial neural network respond surface method is proposed to solve reliability problems,and the proposed improved cuckoo search algorithms can reduce the computation expense and improve the accuracy of the solutions in reliability analysis.Several numerical and engineering applications demonstrate the accuracy and efficiency of the established algorithms.6.The quantitative reliability analysis for the main failure mode of the forward cargo door is carried out.Based on the proposed over-center locking reliability analysis methods of typical mechanisms,reliability analysis of cargo door locking mechanism,vent door mechanism and safety pin mechanism are conducted.Besides,the influence of the gaps and wear for the above three mechanisms is evaluated.Then,the failure probability of the hook structure is calculated by the improved cuckoo search algorithm accurately.Moreover,the fatigue strength failure probability of crucial bolts and lugs under the handle load and the probability of erroneous indication of three indication systems are obtained.Finally,the calculated results are compared with security indicators to make sure that whether they can meet the safety requirements or not.The research contents of this section can provide reference to the quantitative analysis of cabin doors' airworthiness.