Modeling And Analysis Of Assembly Deviation For Heavy Rocket Tank Dome

The dome of heavy rocket fuel tank is composed of large thin-walled structures with non-uniform thickness and unequal opposite sides,and the quality of assembly affects the reliability and bearing capacity of the final products.The non-uniform stiffness distribution of irregular large thinwalled structures leads to non-linear warping deformation during the process of machining and assembly,and it results in a continuous field distribution of deviations in space;Besides,the initial deviation is random distribution due to the fluctuation of actual processing parameters.The deviation description and the analysis model of assembly deviation based on the key feature points are not applicable for irregular large thin-walled structures.It is of great significance to improve the assembly quality and to guide the actual production of the heavy rocket fuel tank dome by proposing an accurate model for the initial random deviation description of irregular large thin-walled structures and carrying out the relationship between the initial deviation of scalloped segment structures and the assembly deviation of tank dome.In this paper,A high-order continuous surface fitting method based on the random deviation information of key feature points is proposed to accurately describe the irregular large thin-walled structures with random deviation.The irregular high-order shell element and its composite element are constructed based on the absolute nodal coordinate formulation,and a new discrete method for irregular large thin-walled structures is established to accurately calculate the deformation by the combination of new elements.The compatible deformation calculation model for irregular large thinwalled structures is proposed based on the assembly static equilibrium equation,and the assembly deviation calculation model for the enclosed structure of fuel tank dome is derived.The geometric accuracy index system is proposed to evaluate the quality of hierarchical assembly for the tank dome.The hierarchical assembly process of the heavy rocket tank dome is simulated by using the model proposed and the comparison with the results of FEM numerical analysis verifies the accuracy of the model.The research in this paper provides theoretical guidance for the design of scalloped segment structures in future heavy rocket tank dome and the prediction and control of assembly deviation.The main research contents of this paper are listed as follow.(1)Accurate description model of random deviation for irregular large thin-walled structureGeometric accuracy index is established to evaluate the quality of irregular large thin-walled structure and the key feature points are defined with consideration of its geometric features.A new fitting method for highorder continuous surface is proposed based on the geometric information of key feature points.Random deviation values with normal distribution are generated based on different geometric accuracy index.Profile fitting model of irregular large thin-walled structures with random deviations is constructed by using the key feature points with random deviation to provide initial input for the assembly deviation analysis.The deviation vector of the discrete point set on the fitting profile is calculated to accurately describe the random deviation field of irregular large thin-walled structures.(2)Modeling of irregular large thin-walled structure based on high-order composite shell elementA new irregular high-order shell element and its composite element based on the absolute nodal coordinate formulation(ANCF)are proposed to accurately calculate the deformation of irregular large thin-walled structures with higher-order slope coordinates and improved shape function,which considers the continuity of the elements at the contact interface.A discrete method of irregular large thin-walled structure is proposed to solve the problem of node connection and deformation coupling between elements with different thickness by using the combination of irregular high-order elements and composite elements.The assembly deformation calculation model for irregular large thin-walled structures is proposed based on the assembly static equilibrium equation.The convergence and accuracy of the new elements are proved by numerical simulation.The influence of the thickened area on assembly deviation and stiffness of scalloped segment structures is studied with the new calculation model,which provides suitable model for assembly deviation calculation of tank dome.(3)Calculation and analysis of assembly deviation for heavy rocket tank domeThe conversion relationship between the point on deviation fitting profile and the node of irregular high-order shell element is proposed based on the random deviation description and discrete model of irregular large thin-walled structures,and the scalloped segment structures with different initial random deviations are constructed.An assembly deviation calculation model of enclosed structure is established for the hierarchical assembly process of the heavy rocket tank dome,and a hierarchical evaluation system of geometric accuracy index is proposed according to the assembly process.The influence of the scalloped segment structures with different geometric accuracy index and different assembly sequence on the assembly deviation of the tank dome are studied.The accuracy of the calculation model for the assembly deviation of enclose structure is verified by comparing the results with numerical analysis.