Wind Resistant Performance And Lightweight Design Of Tower Solar Power Heliostat

Heliostats are significant devices that track the motion of the sun and reflect the sun's rays to a collector in the top of a tower. In the tower solar thermal power plant, hundreds of heliostats are employed for receiving sufficient solar energy, and the construction of which expends more than half of the total cost of the power system, thus heliostats are the most important investment element. Because the tower solar power plants are usually located in open fields where the heliostat is thoroughly exposed to the strong wind, structural deformation occur easily which makes light spot defocus in the collector, thus reducing concentration efficiency and generated output. Even worse the wind-induced overturn and structural failure of heliostat maybe happen. Consequently, a research for the wind resistant performance and lightweight design of the heliostat under strong wind has great significance to improve the safe reliability and durability of the heliostat as well as reduce the power plant cost.This project is supported by the National Natural Science Foundation of China(NO. 51075407) and Chongqing Graduate Student Research Innovation Project(NO. CYB14010). The wind field characteristics, wind-induced response and lightweight design of the heliostat are researched. The major contribution of the work is summarized as followings.(1) A numerical wind tunnel model is established based on the computational fluid dynamics method. The wind field characteristics of the heliostat in 100 positions are investigated to obtain the variation law of the mean wind pressure distributions with the changes of the elevation angle and azimuth angle, and the cause of which is explained. Furthermore, the wind load coefficients, resultant force coefficients and resultant moment coefficients of the heliostat in different positions are analyzed to evaluate the positions with maximum coefficients. According to the power spectrum of fluctuating wind speed and AR model, the time history samples of fluctuating wind speed and the corresponding power spectral densities are derived by Matlab. Meanwhile, the reasonableness and accuracy of the results are validated.(2) Based on the elastic thin plate deflection theory, the mechanical models of the reflector under different boundary conditions are investigated by using small deflection bending model and large deflection bending model, respectively. And then the finite element model is established to verify the correctness of the theoretical model. Moreover, the deflection to thickness ratios of the reflector, which is influenced by wind pressure on reflector and length to thickness ratios are analyzed.(3) In view of the sensitivity of dependence and computational inefficiency in traditional optimization methods for lightweight design of the heliostat, an approximate optimization approach combining response surface model with sequential quadratic programming is proposed to deal with the lightweight design of the heliostat which has nonlinear response with the action of wind based on guaranteeing the strength, stiffness and dynamic property of the heliostat. The static wind load and fluctuating wind frequency are respectively obtained by the numerical wind tunnel model and Davenport power spectrum. The Latin hypercube experimental design scheme and response surface method are combined to construct the second-order response surface models by fitting with 15 design parameters. Furthermore, the response surface models are optimized by using the sequential quadratic programming.(4) In the process of the wind resistant design of the heliostat, only longitudinal wind is considered and vertical and transverse winds are neglected. For this reason, power spectrums of fluctuating wind pressure in different wind directions and AR model are proposed to simulate time history samples for 3D wind field. And then the mean wind loads and fluctuating wind loads are applied to the finite element model of the heliostat. The effects of each direction component of the wind field on heliostat are investigated by evaluating dynamic characteristics and wind-induced dynamic responses of the heliostat in the five positions.(5) The wind load coefficients in various survival stow positions are calculated by the numerical wind tunnel model. In order to explore the best survival stow position for the heliostat under the strong wind, eigenvalue buckling analysis method is introduced to predict the critical wind load theoretically. Considering the impact of the nonlinearity and initial geometrical imperfection, the nonlinear post-buckling behaviors of the heliostat are investigated by load-displacement curves in the full equilibrium process. Eventually, combining B-R criterion with equivalent displacement principle the dynamic critical wind speed and load amplitude coefficient are evaluated.