Dynamic Modeling And Airworthiness Compliance Analysis For Large Commercial Aircraft Structure

This desertation focuses on the dynamic strength problems in development process of the domestic commercial aircraft.Theoritical analysis,finite element(FE)techniques and experiment are used for assisting the structural dynamic and airworthiness compliance analysis.In order to satisfy the experiments and simulation technique rules for structural dynamic and strength in airworthiness regulations,several key techniques and methods are presented in this desertation.The reseach experince in this manuscript will benefit to the dynamic analysis and strength evaluation techniques for both current domestic commercial aircraft and its subsequent versions.Major works of this desertation are listed as follows:(1)The error caused by geometric simpilification is analized by comparing several different type of analytical models that are built by using different simplification critieon.The “L” shape section,which is one of the widely used shape of the stringer in airframe structures,is taken into account in this research.The equivalent FE model of the “L” shape stringer considering computational efficiency and accuracy is presented based on the deformation modes and stress distribution of the detailed FE model.The equivalent model for modelling bolt connection structure is presented either.(2)The degrees of freedom(DOFs)reduction method based on component synthesis technique for localized nonlinear systems is proposed.Considering the airframe structure as the linear system,the airframe FE model are converted to modal space and expressed by a few modal coordinates,while the model of the landing gear system,which is considered as the nonlinear component,is still expressed by the ordinary physical coordinates.By using the synthesis method,the nonlinear component and the linear component are combined together in the hybrid coordinates form.By this way,the total DOFs of the aircraft model is greatly reduced,thus lead to less computational cost when conducting the dynamic response or mode analysis for the aircraft.(3)Based on the relative items in the airworthy requirement,the bird strike FE model of the ARJ21-700 passenger aircraft is constructed.Bird strike analysis has been conducted for the tail wing box of the aircraft,as well as the corresponding verification experiment.The different bird strike locations on the tail wing box are considered,and damage caused by the bird strike has been investigated.The factors which have siginificant effection to the numerical results of the FE model have been determined.A method for improving the bird strike resistance performance of the aircraft is proposed.(4)Acoustic fatigue life is a very important problem to the larger passenger aircraft.According to the aviation regulation item about the fatigue life caused by noise,the acoustic fatigue analysis which is used to determine the possible fatigue part of a larger passenger aircraft has been conducted.The input of the fatigue analysis is the engine noise.Base on the analytical results,the test piece has been determined.The acoustic fatigue test has been carried out to verify the validation of the fatigue life of the aircraft.(5)Based on the stress mode analysis,a method for detecting the stress raiser of the airframe structure under white noise exciting is proposed.Then,the fatigue life predict method for the structure under vibration environment is proposed.The crack on the tail wind's fairing supporting structure of the ARJ21-700 aircraft has been investigated by using the proposed method.Based on the numericalresults,the improvement design for the supporting structure has been proposed,and the fatigue life of the improved structure has been validated by using both analytical and experiment method.(6)The FE model of the ARJ21-700 aircraft and its fuel lines system are estabilished for the aircraft force-landing analysis.In order to accurately describe the deformation and damage caused by the impact under force-landing situation,the fuel lines system is modeled in a very detail form,including with the models of the flexible joints between the fuel lines.Numerical simulation,which is used to evaluate the strength of the fuel line system under force-landing situation,has been conducted after determing the technique restrictions required in the CCAR/FAR 25.994 rules.The stress raiser and impact force limitation of the ARJ21-700 aricraft's fuel line system under the force-landing situation is determined by using the FE analysis.