Study On Non-linear Statics,Kinematics And Dynamics Of Cable And Cabin System For Large Radio Telescope

FAST (Five hundred meter Aperture Spherical Telescope) is a project of constructing the largest radio telescope of the world in Guizhou Province, China. Optomechatronics on Synthetic Design for Feed Support and Control System, with higher precision and low cost, is applied in the FAST project. Cable-suspension sustaining feed system characterized with the flexibility, as a parallel mechanics, is largely different from other rigid parallel manipulator commonly known as the Stewart platform. With a huge working space, low cost and less requirement of environments, this new type parallel mechanics has been a hot point in the field of parallel manipulator, simultaneously, as a key technology and the most challenging part of FAST, it has been focused in by the astronomer and antenna experts all over the world. However, at present time, it is still open, the existing studies have not established uniformed theories and methods yet. The purpose of this dissertation is to study the related theories and methods on establishing mathematics, mechanics and computational models of non-linear statics, kinematics and dynamics for cable-suspension feed system. There are seven chapters in this dissertation as follows.Chapter 1 PrefaceThe research background and target of new generation large radio telescope are presented. The technical features and research contents of cable-suspension feed system are described. The current study on parallel cable mechanics is reviewed. Several issues that have been studied and the progresses have been made in this dissertation are proposed.Chapter 2 Non-linear static analysis of the cable-suspension systemNon-linear static mathematics and computational model of cable-suspension feed system is established. Pseudo-drag problem of flexible cable is described and the critical criterion is deduced. The problems of solution space and unique solution of system are defined and discussed. Two optimization principles are proposed to distribute the load ideally among cables, thereby avoid pseudo-drag. Based on the movement laws of cabin, and considering the force condition in cables, a 8-cable suspension feed system, which can completely remove the no solution surfaces in 6-cable system, is presented and designed by means of adding 2 down-ward cables. A solving method, whose feasibility is proved, is developedfor static equilibrium equations of the cabin.Chapter 3 Research on driving forces in the cable-suspension feed systemDynamics equilibrium equations of the feed cabin are deduced. Inverse kinematic and dynamic mathematics and computational model are established by discretizing cable into flexible cable-rob body. When cable interacted under the load both of gravity and inertia force, derivative equation of cable's defection curve in space is deduced to study cable's rigidity movement, and flexible deformation is also determined by finite element method. An iterative algorithm of rigid-flexible body is developed to compute driving force of system if the position, posture, velocity and acceleration of feed cabin are known.Chapter 4 Time-dependent computational simulation of the response of cable-suspension feed system in gusty windBased on the time-independent structure finite element method, and with consideration of the movement laws of cabin, a 3-D time-dependent structure finite element model formulated by a new method named ISS method (Instantaneous Structure Supposition method) to deal with the vibration response of cable-suspension feed system in gusty wind is presented. In the model, all sources of geometric non-linearity, cable sag and changes of cable geometry due to large displacement, are fully considered. In time domain, turbulent wind load is simulated by applying cosine series. The Newmark- P step-by-step numerical integration algorithm is used to calculate the response behavior of system when feed cabin locates at a certain position (typical location) and when feed cabin moves along a certain trace (time-dependent structure). Compared with the data...