| Space mesh deployable antenna is a kind of space deployable system composed of the deployable mechanism,the metal reflecting surface and the cable net structure.With the development of spacecraft structures in the direction of large diameters,The mesh deployable antenna becomes a hot research spot of many countries.However,at present,the space antenna has problems of large mass,low stiffness and low shape accuracy,which restricts the application of large deployable antennas in space missions.In this paper,through the application of flexible cables,a cable-rib tensioned deployable antenna is innovatively designed.Compared with the traditional truss articulated deployable antennas,it exhibits higher stiffness and lighter weight.This study take the large-caliber cable-rib tensioned deployable antenna as the research object,conduct deeply exploration on the key technologies such as deployment mechanism design,nonlinear mechanical modeling,structural parameter optimization,cable net form finding and precision adjustment,and simulation experiment.Considering the large-caliber requirement of space net deployable antenna,this study proposed a cable-rib tensioned deployable antenna mechanism.Considering the requirements of the focal length ration,deployment function,and folding rate of the antenna system,the relationship between the geometric model of the deployable unit and the geometric parameters is established.Besides,a index was established to evaluate the number of units of mechanism,and the optimal number of unit is determined.The stiffness-based cable importance analysis method is proposed,and the arrangement form of the tensioned cables in the antenna mechanism is determined.Moreover,the mathematical models of prestressed cable and beam element are established,and the nonlinear influence of pretension on cable and beam element is analyzed.The results lay a theoretical foundation for the subsequent analysis of the overall stiffness of the cable-rib structure.To predict the dynamic characteristics of the antenna structrue after deployed,based on the geometric nonlinear finite element method,the geometric nonlinear stiffness term,which is related to the pretension distribution of the structure,is added to the traditional model,and established the analysis model of nonlinear cable element and beam element with pretension respectively.The iterative process of the element stiffness matrix and internal force is given.Through the node coordinate matrix and the component connection matrix,the component vector matrix of the deployable mechanism is established,and the functional relationship between the mathematical model and the structural parameters of the antenna deployable mechanism is determined.The geometric nonlinear dynamic model of the cable-rib tensioned antenna is established by adding zero processing and matrix transformation.The eigenvalue decomposition problem is solved by subspace iterative method.The modal analysis of the deployable structure is carried out,and the natural frequency and mode shape are obtained.Results show that the pretension of the cable plays an important role in the stiffness of the whole structural system,reflecting the nonlinear characteristics of the cable-rib tensioned antenna.The method can be applied to the dynamic modeling and solving of any prestressed structure and cable-beam structure.Due to the application of a large number of tensioned cables in the antenna mechanism,the distribution and magnitude of the pretension of the tensioned cable are directly related to the performance of the deployable antenna.Therefore,a pretension design method is proposed in this paper,which is different from the conventional force density method.Based on the nonlinear finite element method and genetic algorithm,this paper considers the influence of the flexible deformation of the antenna structure.Taking the shape accuracy and stiffness of the antenna structure as a constraint condition,and the pretension value of each tensioned cable as the design variable,this study establishes the pretension distribution optimization model of the tensioned cable.Simulation analysis is performed.A structural parameter optimization method is proposed to achieve the maximum stiffness/mass ratio of the antenna under natural frequency constraints.The numerical simulation results demonstrate the effectiveness of the proposed method.Based on this,the detailed design of the antenna structure scheme is carried out.To determine the cable net structure of the antenna,this paper proposes a mesh division method considering the sag effect,analyzes the error of the parabolic surface fitting accuracy of the cable net,and determines the ideal length of each cable segment of the antenna parabolic cable net structure.Then,through the node coordinate matrix and the component connection matrix,a parametric mathematical model of the cable net structure is established.On this basis,based on the force density method and the nonlinear finite element method,a method for determining the configuration of the cable net considering the deformation of the deployment mechanism is proposed.By taking the force density of each cable section as the design variable,and the surface accuracy of the cable net structure and the uniformity of internal tension as the optimization target,the iterative optimization model of antenna cable net structure is established.The model also analyzes the deformation of the deployable structure as a parameter in the process of shape finding,and establishes the cable net shape forming finding optimization model under boundary deformation.Compared with the traditional method,the proposed form finding method considering the deformation influence of the deployable structure can significantly improve the shape accuracy.Finally,to solve the problem of the accuracy adjustment of the cable net structure,a cable net precision adjustment optimization model based on the node adjustment method is established,which realizes the rapid adjustment of the cable net accuracy.To verify the feasibility and theoretical correctness of the proposed deployable antenna,a experimental prototypes was designed according to the deployable principle of the mechanism.The experimental research on the deployment accuracy,static stiffness,dynamic stiffness and mesh surface accuracy of the cable-rib deployable antenna was carried out.The experimental results show that the mechanism has good deployable performance.The dynamic test results and the measurement results of the mesh surface accuracy are compared with the theoretical model analysis results to verify the correctness of the theoretical model. |
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