| Five-hundred-meter aperture spherical riado telescope (FAST) is expected to be the largest telescope among those telescopes in the plan or under construction in the world. FAST pioneers a new model for constructing the giant telescope. The reflector structure as the main part of FAST is essentially a lightweight and complex cable-net structure with a super-long span and a real-time adjustable shape. Though the results in structure scheme, shape-state optimization, shape-changing strategy and etc, have been achieved during the 13-year preliminary research. However, the key issues of structural safety and accuracy control is still not studied in-depth in the previous research, and obviously, these issues will have a significant impact on the construction, running and maintenance of FAST. The research on these issues is urgent for the construction of FAST, and also has a broad application in other similar giant radio telescopes because it is nearly at blank stage for those structures. Therefore, the research is of obviously engineering applicatoin value and theoretical innovation significance, and needs in-depth study. The main contents in this paper are shown as following.1. Simulation and effect analysis of non-uniform solar temperature field of FASTThe finite element model of FAST in the actual environment for structural temperature field analysis is established, with the factors of solar radiation, shadow in surrounding environment, periodic air temperature and etc taken into consideration at the same time. The non-uniform solar temperature field is computed using the transient analysis method, and subsequently, the RMS values of fitting of the reflecting surface for working paraboloids in different locations of the spherical cap under sunshine are analyzed. The results show that the impact of the non-uniform solar temperature field on RMS values should not be ignored. Finally the control method of RMS value under sunshine is proposed according to the structural features and characteristics of the temperature field.2. Parameter sensitivity analysis of FAST structureThe advantages and disadvantages of various methods for parameter sensitivity analysis are summarized and analyzed. According to the characteristics of FAST reflector structure, the paremeter sensitivity analysis method based on random sampling and correlation is proposed, and in order to solve the calculation difficulty induced by random sampling and matrix operations of large-scale parameters, the LHS sampling method and correlation coefficient significance test method, are introduced. The probability-0statistic models of FAST structural parameters are established based on practical situation, and the influence of structural parameter random errors on RMS value is obtained by a great lot of computations. Finally, suggestions for accuracy control of structural parameters are presented.3. Shape-changing fatigue analysis of FAST structureThe requirement analysis of fatigue life is carried out according to the working mode of longtime sky survey and independent random tracing observation, and the computation method of shape-changing fatigue stresses is proposed and programmed based on sofewares of MATLAB and ANSYS. And then the simiplication method of life-cycle stress course is put forward, the realtime rainflow counting method for random and variable amplitude stress course is programmed. Subsequently, the structural fatigue life is calculated by numerical simulation based on S-N test curve and Miner linear cumulative damage method, and the statistical distribution of fatigue life and fatigue risk zone are obtained. Finally, the fatigue property of strand cable and steel rod is tested.4. Fault diagnosis and safety assessment of FAST structureThree basic modes of structural failure are presented according to the structural features and the active shape-changing work mode, and the method for structural fault diagnosis is proposed and studied to realize the on-line diagnosis of structural fault region and off-line diagnosis of failure members. The method for structural safety assessment is proposed, which is aimed at the two leading indicators of structural long-term safety, the residual fatigue life and the static safety stock. Then the two methods are programmed and validated by numerical simulation.5. Development and integration of structural health monitoring system of FASTThe frame, functions and monitored variables of the system are determined according to the characteristics of FAST reflector structure. The optimal lectotype and location of sensors are analyzed, the hardware for acquisition is selected in reason, and the transmission wiring scheme is designed. The integrated software system for health monitoring is developed with the functions of automatization and visualization, synthetically using softwares of LabVIEW, MATLAB, ANSYS, Delphi and etc, and wherein the core modules for active shape-changing analysis, structural fault diagnosis and safety assessment and ect are programmed. The monitoring system has already been applied in the stretch forming test of FAST 30m model.
|
PDF Full Text Request