Thermally Induced Vibrations Of Deployable-net-reflector

The deployable cable-network antenna has become a promising option for antenna of spacecraft, due to the features of high packaging efficiency, light weight as well as high precision. During the life cycle of a deployable antenna from design to the in-orbit operation, very different mechanics plays the essential role in different states, such as form-finding of tensegrity structures, multi-flexible body dynamics, structural vibration, etc. In this thesis, we numerically investigate the thermal-induced vibrations of cable-network antenna at its fully deployed state under solar radiation. In order to build appropriate pretension in the cables, the form-finding problem is also studied.First, the existing form-finding methods are reviewed with an emphasis on force density method, which is adopted in this thesis for form-finding analysis of independent cable network with fixed boundary nodes. We show that the pretension state and node position of antenna cable reflector will be far away from the form-finding design with the truss frame become more flexible, which is the consequence of antennas with larger diameter or lighter weight.We then proposed a method of form-finding procedure to produce the desired shape of cable reflector considering the large deformation of the antenna’s truss frame. The formfinding is actually an iterating process between the traditional force density method and the finite element analysis with geometrical non-linearity. The form-finding algorithm is realized in the commercial finite element software ANSYS, and then cable reflectors of three typical topologies are analyzed with the proposed method. Based on the results, the proposed formfinding method can maintain the accurate parabolic reflector shape even when the truss frame has significant distortion, showing superiority than the traditional methods considering fixed boundary or small deformation of frame.Based on the form-finding process, the dynamic analysis model of whole antenna with pretensioned cable net is built. In ANSYS environment, a non-standard coupled thermalmechanical procedure is developed to calculate the thermal induced vibration of the antenna with high efficiency. The analysis establishes temperature exchange between transient structural analyzing using beam/cable elements and thermal analysis using shell elements, in order to effectively simulate the temperature gradient in beam section which is essential for the determination of thermal moment. The method is verified by several well studied simple cases. Then the thermally induced vibrations of deployable antenna are simulated under four typical thermal radiation directions, both cases with and without pretensioned cable reflector are analyzed and compared. The results show that the whole antenna structure will generate average deformation of millimeter level under solar radiation, but the vibrating amplitude around the average deformation is very small. The average deformation gets stable until the heat conduction arrives at the balance across the antenna. It is also found that the pretensioned cable changes significantly the deformation modes of the antenna under radiation loads, also the average deformation and vibrating amplitude of the frame are both reduced for the for investigated radiation cases. Meanwhile, the nodes of cable reflector also displace in the same order of magnitude with the frame.