Approximate Dynamic Modeling Of A Large Full Steerable Reflector Antenna

The very large full steerable reflector antenna with 110m diameters in Qitai, Xinjiang Province- QTT (QiTai Telescope) is the largest telescope of the world under researching. One of its important performance indexes is the pointing accuracy. In order to meet this index, the pointing control is needed. But the total degrees of freedom are too large to control in time. So this paper mainly focuses on the approximate dynamic modeling for this antenna.1. The finite element of the antenna is established considering the structure demand and design requirement of QTT. The mass of the panel is equivalent to mass elements on the nodes of beam element. The large gear is built using shell element. Beam element is used to simulate the gear meshing. Four groups of short beam element and shell element connection simulate the roller and the constraints. Thus QTT finite element model is established, and analysis illustrates that the model is correct under static and dynamic load.2. The main modes are selected. Due to the complexity structure of QTT, the complete dynamic model of the antenna is difficult to control in time, model reduction is needed. From different aspects, the reduction is based on modal mass, energy response and norms of system transfer function in frequency domain. The approximate dynamic model of the 20 bar truss structure in plane is established based on the above methods. The advantage and disadvantage of these methods are analyzed.3. The approximate model is established. (1) The simplified model of QTT is established in consideration with its actual sizes. (2)Based on the transfer function method, the main mode affecting the antenna pointing errors are selected, for the QTT and its simplify model. (3)The approximate dynamic model of the simplified model and QTT are established using ANSYS and ADMAS. Finally, pointing error calculation formula is deduced.4. The simulation of the approximation dynamic model is made. (1)The simulation of the approximate and the total dynamic model of the simplified model of QTT have made to prove the validity of the mode selection. (2)The simulation of tracking a moving target based on the approximate model of QTT has made. The dynamic response and real-time tracking error of the antenna are gotten. The research in this paper lays a solid base for the researches on the pointing control of the very large full steerable reflector antennas in future.