Structural Design,Analysis And Active Shape Control For Space-borne Radial Rib Mesh Antenna

In recent years,with the growing demand for satellite mobile communication and the in-depth research in the fields of earth observation,radio astronomy and electronic surveillance,the design requirements of the antenna gain are higher and higher,and the requirement of antenna aperture is larger and larger.However,due to the limitation of loading space of carrier rocket,the deployable structure is the best way to realize large antenna aperture.Among various deployable space-borne antennas,the cable-net antennas have been widely concerned by researchers in various countries due to their characteristics of high folding ratio,light weight and wide adaptive aperture range.The Chinese researchers have carried out a lot of works on the perimeter truss mesh antenna.However,there are few researches on the new generation of radial rib cable-net antennas which have better performance and wide application.Focusing on the radial rib cable-net antenna and aiming at how to reduce the design errors and in-orbit errors,this thesis studied geometric design,form-finding analysis,electromechanical coupling dynamics modelling and active shape control.The research of this paper provides new design ideas and methods to develop a new generation of radial rib mesh antenna with large diameter and high accuracy,and also lays a systematic theoretical foundation for the engineering application of radial rib cable-net antenna.The main work of this paper is summarized as follows:(1)Combined with the characteristics of geodesics and equilateral triangles,a quasi-equilateral triangle grid method is proposed based on iteration strategy of node coordinates.The proposed reflector cable-net is superior to other methods in terms of the total length of the cable,the uniformity of the cable elements and the precision of the cable-net surface,especially when the focal diameter ratio of the reflector surface is smaller.Two kinds of reflector surface cable-net under different boundary constraints are generated using the quasi-equilateral triangle grid method,and then two kinds of radial rib cable-net antenna geometry configurations are designed,in which the 6 rib reflector surface grid is more uniform and the 12 rib configuration has higher utilization ratio of reflector surface.(2)A hybrid form-finding analysis method for determining the equilibrium configuration of the radial rib mesh antenna is presented.For the reflector cable-net,the minimum norm method is used to find the optimal distribution of pretension according to the designed cable-net configuration.While for the rear cable-net which has no precision requirement of the shape surface,the force density and non-linear programming were combined to carry out form-finding and force-finding analysis.This strategy of structure splitting and from-finding step by step releases some geometric constraints of the rear net and reduces the difficulty of each form-finding analysis,which makes the method more flexible and applicable.The results show that this hybrid method can effectively deal with the problem of form-finding and force-finding analysis for the radial rib mesh antenna,and obtain reasonable pretension distribution.In order to reduce the deformation effect of pretension on the radial ribs,a kind of radial rib support structure with auxiliary cable is also proposed.(3)The electromechanical coupling dynamic model of the radial rib mesh antenna with PZT actuators is established.For the deployed radial rib mesh antenna,the passive cable element and the radial rib element are modeled by two nodal bar element and space beam element respectively,while the dynamic finite element model of PZT actuator element is derived based on the piezoelectric constitutive equation and Hamiltonian principle.The electromechanical coupling dynamic model of the whole structure of the mesh antenna is obtained by integrating the element models under the global coordinate system.The results show that a larger base frequency of the structure can be obtained by applying the fixed constraint on the ends of the auxiliary bar,which can meet the general design requirements.After the actuator is added,the modal frequency of the structure decreases,and the higher pretension can make the modal frequency of the structure larger.(4)An active shape control method for radial rib mesh antenna based on improved fast model predictive control(IFMPC)is proposed.Using the Newmark-? method,the dynamic equation of the radial rib mesh antenna is expressed as dynamic explicit format,which solves the problem of large storage and low efficiency caused by matrix exponential operation in traditional model predictive control.On this basis,a strategy of variable weighting coefficient matrix and a fast calculation method of control coefficient matrix are presented to further shorten the control time and improve the calculation efficiency.The simulation results show that this method is suitable for solving large-scale structural shape control problems,can significantly reduce the residual vibration generated in the shape control process,and has good robustness to the interference in the control process.