| Cable-network antennas are a new type of large flexible space structures developed in the requirement of space missions, which have the vital significance for various space applications such as high-resolution electronic reconnaissance and high-quality satellite communication. This breed of antenna structures, with the advantages of light structural mass, high stowing ability and large aperture application range, denotes an ideal structural form of spaceborne deployable antennas. However, its shape accuracy is the main effect factor of the antenna performance. During the stages of design, manufacture and in-orbit flying, there exist many kinds of factors influencing the surface accuracy. Since such antenna has the features of shape-force intercoupling and displacementstress nonlinearity, analyzing the shape error characteristics becomes an extremely challenging topic, and yet there are a little of relevant literature regarding the research on high precision mesh configuration determining theory and systematic shape- error analysis methodology. Aiming at the urgent requirement of future space applications for cable-network antennas with lager aperture and higher surface precision, this dissertation systematically addresses a study on the mesh configuration theory, nonlinear dynamic modeling and shape error analysis of spaceborne large cable-network antennas through the aspects of theoretical analysis, numerical simulation and ground experiment. The main work of this dissertation can be summarized as below:1. The basic theoretical question of mesh configuration determining for cablenetwork antenna structures has been studied, and high precision mesh configuration determining methods based on the basic theory have been proposed.(1) By synthetically considering all the factors having effect on the final mesh configuration, such as geometric topological forms, boundary connection conditions and shape determining criterion, etc., a theoretical foundation of mesh design and configuration determination for complex cable-net structures has been constructed.Two approaches, namely the cyclosymmetry method and the topological mapping method, are proposed for designing the mesh geometric topological forms, and three shape forming criteria, named as the equal force-density, equal force and equal length criterion respectively, are set up, and thus the theoretical foundation for determining the mesh configurations of complex cable-net structures is formatted.(2) By treating the tension provided by the vertical tension ties as the external forces, a basic mesh configuration determining method is proposed. Then, taking the flexibility of the ring truss structure into account, an exact mesh configuration determining method considering the effect of truss deformation is proposed. Furthermore, focusing on the entire antenna structure, an integrated high precision mesh configuration determining method is proposed, which is applicable to both prime-focus and offset parabolic antennas.(3) Numerical simulation analysis regarding the proposed innovative methods such as the cyclosymmetry method and the topological mapping method are carried out. The results demonstrate that: the cyclosymmetry method is suited to generate arbitrary polygon-faceted meshes; the topological mapping method is appropriate for generating triangle-faceted meshes with different mesh-grid density; and the exact mesh configuration determining method considering the effect of truss deformation is suitable for the mesh generation of cable-network antennas operating at high frequencies.2. The nonlinear dynamic modeling for cable-network antenna structures has been studied.(1) Using the geometric nonlinear finite element(FE) theory, the nonlinear element model of cables with internal tension and that of truss rods with internal compression are respectively deduced, in which the influence of the structural internal forces on the stiffness matrix is well considered.(2) According to the idea of ―first the element, then the component, and then the system‖, the geometric nonlinear FE model of the entire cable-network antenna structure with internal forces is established.(3) The structural dynamic characteristics and their influencing factors are analyzed. The results show that: improving the internal tensions can increase the structural stiffness and thus raise the system natural frequencies, while accounting for the internal compressions of the support truss, the natural frequencies of the entire antenna structure is decreased slightly.3. The methodologies for analyzing shape errors of cable-network antenna structures has been studied.(1) Focusing on the shape error problem due to the variation of cables, two computing models, named as tensile cable-net model and tension truss model respectively, are presented. The tensile cable-net model has considered the internal tension variation caused by the change of cable length, which has a high computational accuracy; while the tension truss model is relatively simple and has a relative high solving efficiency.(2) Aiming at the mesh distortion problem due to the in-orbit flying conditions of the antenna, two deformation predicting mothods, namely the iterative method based on the FE model and the iterative method based on the entire tangent stiffness model, are set up. Research demonstrates that: the FE model-based iterative method can exactly predict the deformation of antennas under various loads in out space, but its computing process is complicated, while the entire tangent stiffness model-based iterative method does not require the process of FE assembling and is much easier to solve, but it only can be applicable to the single cable-net structure.(3) Taking advantage of the proposed computing and predicting models, numerical simulation about the shape error analysis due to the cable length manufacturing error and in-orbit flying conditions are conducted. The results illustrate that: the cable-length error will cause a decrease of surface accuracy in a certain degree; for those loads coming from space environments, the disturbing loads such as the disturbing force due to the nonspherical shape of the earth has little effect on the shape accuracy so that can be neglected, while thermal loads have a significant effect on the antenna surface precision; the change of spacecraft flying conditions such as rapid orbit maneuver also greatly influences the shape precision of the antenna.4. The experimental research on the mesh deformation characteristics of cable-network antenna structures has been conducted.(1) According to the proposed mesh configuration determining method, a prototype workpiece of cable-network antenna with aperture of 1.225 m is designed and fabricated, and the structural deformation measuring experimental system for the cable-network antenna structure is built.(2) Experiments for measuring the surface accuracy and the mesh distortions of the cable-network antenna are carried out. The experimental results demonstrate that: the measured value of the surface accuracy conforms to the designed value, thus the effectiveness of the proposed mesh configuration determining method has been illustrated; the relative error of the deformation measured value to the predicted value is very small, thus the correctness of the proposed deformation predicting model has been verified.The above researches could provide theories and methodologies for the mesh configuration determining, dynamic characteristic analysis and shape error characteristic investigation of this type of large complex flexible space structures, and provide theoretical reference and technical support for the design, manufacture and application of the spaceborne large cable-network antenna structure. |
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