Compliant Assembly Variation Analysis Of Aeronautical Thin-Walled Structure Based On The Substructuring Technique

The complex structure of airframe and the large number of parts in it make its assembly process time consuming,workload taking,and a major part of the overall airplane manufacturing process.The assembly variation casts significant influence not only on the aerodynamic characteristics and structural reliability of the manufactured airframe,but also on the efficiency of its manufacturing process.Assembly variation analysis is an effective theoretical tool to analyze and control the propagation of assembly variations.Currently,the assembly variation analysis on airframe is mainly conducted with the traditional kinematics-based methods,which however can only deal with the locating process.Most of the parts in airframe are of thin-walled structure,have complex interactions with each other and undergo significant deformation in their assembly process.The mechanics-based compliant assembly variation analysis method can take more product and process factors into account and get more accurate results.However,the existing compliant assembly variation analysis methods have tedious modeling process,neglect the simultaneously arising stresses,and take no account of the stiffness variation in assembly process,which make them not well-suited for the assembly variation analysis of aeronautical thin-walled structure.Compliant assembly variation analysis methods in the full sense were developed with some kind of model reduction technique,to reduce the large amount of computation that comes from the combination of finite element method and statistical analysis.As a typical model condensation technique,the substructuring technique can flexibly set the condensation conditions,completely recover the condensed information and make amendments of the condensed model,which make it possible to overcome the limitations of current compliant assembly variation analysis methods.Based on the substructuring technique,and in light of the assembly process of aeronautical thinwalled structure,this dissertation formulates the efficient modeling of deviation propagation,conducts collective variation analysis of assembly deviations and assembly stresses with the Deviation Propagation Model(DPM),and further,taking into account the structural stiffness variation due to residual assembly stresses,the relative update of substructure is discussed and an update-substructure based nonlinear analysis algorithm is developed.All these eventually establish an innovative compliant assembly variation analysis method for aeronautical thin-walled structure.The main contents and contributions of this dissertation are as follows:(1)Modeling of deviation propagation of thin-walled structure assembly using substructuresIn light of the assembly process of aeronautical thin-walled structure,and combining the condensation flexibility of substructuring technique,an efficient modeling method for deviation propagation is proposed.Firstly,by discussing the multistep assembly process oriented substructure generation and the repetitive structure oriented substructure transformation,the substructuring method of compliant parts is proposed;then based on the part substructures,and by decomposing the assembly process into element subprocesses and introducing the additional assembly boundary conditions,the deviation propagation modeling method for typical assembly process of aeronautical thin-walled structure is developed;and finally,with Monte Carlo(MC)simulation on the constructed DPM,statistical variation analysis is conducted.With a great reduction of model size and without loss of accuracy,the proposed method largely reduces the number of finite element analysis runs needed in the modeling process and significantly improves the modeling efficiency.(2)Collaborative variation analysis of assembly deviations and assembly stressesIn light of the comprehensive demand of high geometric accuracy and low stress level of aeronautical thin-walled structure assembly,and combining the information completeness of substructuring technique,a collective variation analysis method of both assembly deviations and assembly stresses is proposed.Firstly,by introducing the Output Transformation Matrices(OTMs)into the part substructure system,analysis of assembly stress based on the recovery from assembly deviation is achieved;and further,the transformation of OTMs and the evaluation of assembly stresses are discussed;then finally,statistical analysis of both assembly deviations and assembly stresses is conducted by integrating the stress analysis into the MC simulation based statistical variation analysis.The proposed method achieves collective variation analysis of assembly deviations and assembly stresses with the same substructure-based DPM and extends the scope of analysis.(3)Substructure updates considering the stress stiffening effect of thin-walled structuresIn light of the stress stiffening effect in thin-wall structure assembly process,and combining the amendability of substructure,the structural stiffness variation due to residual assembly stresses is analyzed,and taken into account in the compliant assembly variation analysis by updating the substructures.An update-substructurebased nonlinear analysis algorithm is developed: the Neumann series are adopted to improve the substructure updating efficiency;a piecewise-linear strategy is proposed for the solution of nonlinear DPM;and low discrepancy sequence is introduced as a substitute for the pseudo random sequence used in MC simulation to accelerate its convergence.The proposed method takes stiffness variation into account in the substructure-based DPM and enhances its applicability in nonlinear conditions.(4)Assembly experiments of aeronautical thin-walled structure and accuracy validation of developed methodTwo sets of assembly experiment are conducted to validate the simulating accuracy of the developed method.The experiments are performed on a set of simplified panel subassembly and a set of side fuselage panel subassembly,respectively.The experiments are designed concerning the part structure,fixture layout,assembly process and measuring scheme.The postprocessing method of measuring data is discussed.And finally,validation is made by comparison of the measured data and simulated results.In the simplified panel subassembly experiment,it is observed from the views of predicting the magnitudes,spatial distribution and process evolution of assembly deviations respectively that the developed method has a very high accuracy.And in the side fuselage panel subassembly experiment,it is showed that the simulating accuracy of the developed method can meet the engineering demands in complex engineering conditions.(5)ApplicationsBased on the above research,computation programs for the conduction of substructure-based compliant assembly variation analysis are developed,concerning the information input and preprocessing,deviation propagation modeling of assembly process,MC simulation,substructure updating,and postprocessing and output.The developed programs are applied to practical engineering cases such as the exhaust pipe mounting.From a comprehensive view of controlling both geometric accuracy and residual stress,different designs of assembly schemes,tolerance schemes and part structure are quantitatively analyzed and compared,providing an effective guidance to the airframe product and process design for assembly quality.The research in this dissertation achieves efficient,comprehensive and accurate analysis of the thin-walled structure assembly variation.The proposed method can apply not only to airframe,but also to other thin-walled mechanical products.