Compliant Assembly Deviation Modeling And Deformation Compatibility Calculation Of Large Scale Thin-walled Structure

Large scale thin-walled structure constitutes the framework of aircraft,launch vehicle and space station,which is the main load-carrying structure in these equipment.Therefore the assembly deviation of thin-walled structure has a great influence on the performance of the whole structure.A precision description of deviation of thin-walled structure is difficult to achieve due to its weak stiffness and large geometry nonlinear deformation.The rotation deformation of thin-walled structure could not be calculated accurately with conventional deviation models.The coupling of assembly deviations propagation is very strong due to the enclosed feature of thin-walled structure,which makes the prediction and compensation of assembly deviation very difficult.For the lack of the transfer rule of assembly deviation,the ‘trial and error’ method is always applied for the control of assembly deviation in engineering field,which affects the assembly quality and efficiency in practical application.Aiming at the deviation modeling and deformaiton compatibility calculation of large scale thin-walled structures,several new higher-order beam/plate element models and stiffened plate element are proposed based on the absolute nodal coordinate formulation(ANCF).These models could be used for the accurate description of large rotation deformation of structures.The ANCF method is introduced to the assembly variation analysis of thin-walled structures for the first time in this thesis,with which the mechanical calculation model for deformation compatibility of structure assembly is established.Several typical deviation models are defined due to the geometrical feature of thin-walled structures.Based on the transfer function model and quality index system of assembly deviation established in this study,the transfermation and accumulation rules of bias field for closed thinwalled structures under various parameters are studied quantitatively.A vertical assembly experimental platform for thin-walled structures is designed,with which the assembly of thin-walled structures and deviation measurement experiments are conducted for the verification of the effectiveness of the method proposed in this study.Main research contents of this thesis focuses on the following parts:1)Design of new stiffened plate element models based on the ANCFA new irregular quadrilateral plate element is established by modifying the shape function of the conventional plate element,with which the distortion problem in the description of complex surfaces can be solved.To circumvent Poisson and shear locking problems associated with the conventional ANCF elements,several new higher-order beam/plate element models are proposed.High order polynomials are employed to the element displacement function,as well as higher-order slope coordinates which could enrich cross-section deformation mode and interpolation order are introduced.The effectiveness of new elements to improve the accuracy and efficiency in numerical simulation are verified.By considering the arrangement form and geometric constraints of stiffeners,the equation of deformation compatibility and coordinate transformation matrix between beam and plate elements are deduced.Moreover a universal method for establishing stiffened plate elements with various geometrical continuities and performances is proposed.The effectiveness and performance of various stiffened plate elements are studied with several numerical simulations.2)Calculation model of deformation compatibility for large scale thinwalled structure under overconstraint clamping conditionThe stiffness matrix of initial curved element is deduced by considering material anisotropy and geometrical nonlinearity of large scale aluminum alloy thin-walled structure.The ANCF method is applied to the calculation of deformation compatibility of thin-walled structures for the first time.With the help of slope coordinates of ANCF elements the large rotation deformation of thinwalled structures could be described accurately.Several basic deviation models are proposed according to geometrical features of thin-walled structures,with which arbitrary deviations structure could be obtained.Based on these deviation models the assembly deviation transfer law of thin-walled structures could be studied quantitatively.A calculation model of deformation compatibility for large scale thin-walled structures is established based on the quasi static hypothesis.The mapping relation between structure elastic energy and initial deviation is analyzed by using fitting function.Based on above study a deviation transfer model is proposed,which lays the theoretical foundations for fast and accurate calculation of assembly deviation for thin-walled structures.3)Calculation and analysis of deformation compatibility for compliant assembly of large scale closed thin-walled structureA mechanical calculation model of deformation compatibility for large scale closed thin-walled structures assembly is established,which contains four steps including positioning,clamping,sizing and assembling.An assembly quality evaluation index system is proposed,which is constituted by mathematic models of profile tolerance,generatrix straightness,roundness and cylindricity.The transformation and accumulation rules of deviation field during the assembly of closed thin-walled structure are investigated with numerical simulations,as well as the effects of initial deviation,assembly sequence,constraint form and geometric parameters on the assembly quality are analyzed.The influence of stiffness mutation caused by the last closed connection step on the deviation redistribution is also investigated,which provides the theoretical basis for deviation prediction and compensation in engineering fields.4)Experiment verification for deformation compatibility of thin-walled structures compliant assemblyA vertical assembly experimental platform and several fixtures for thin-walled structures are designed,as well as the experimental processes for structure assembly and deviation measurement are developed.Based on this platform,assembly experiments are conducted for large diameter-thick ratio thin-walled structures with various dimensions.The appearance morphology of structure before/after assembly is measured by using the laser scanning device.The deviations of structure before/after assembly are evaluated by using the evaluation index of profile tolerance.Assembly deviations of the same thin-walled structures obtained by the new method proposed in this thesis and the conventional method are compared with that of the experiment results,which proves that the new method has higher precision and efficiency when dealing with the calculation of deformation compatibility for large diameter-thick ratio thin-walled structures assembly.The new method could be applied for optimization of structure maching before assembly,which avoids the trial and error process in engineering fields.A set of assembly deviation modeling and deformation compatibility calculation method for large scale thin-walled structures is formed in this thesis,which provides basic theory and technical method for deviation prediction and compensation of large scale thin-walled structures assembly.