Study On Wind Turbine Blade Layers Optimization Design Under Extreme Loads

Blade Structural design on Large-scale wind turbine blade mainly focuses on blade layers design. Carrying out the study on the blade layers optimization is meaningful for reducing the blade cost, making up the functional defects of existing analysis software and improving the efficiency of blade design. Because during the process of blade layers design, many design requirements, variables and objectives need to consider, it is complex to build the optimal design model. Especially, computing the ultimate bending moment, maximum blade tip deflection, ultimate strength and other design requirements which are related to the load are complicated and time-consuming, they need to deeply research and build proper models. Hence, this article will study on the optimization algorithms used for the blade layers optimization and some design requirements, which aims to build a wind turbine blade layers optimization design model under extreme loads to be used in different blade layers design. The following research works have been finished.Firstly, based on the modified single-objective particle swarm optimization by the author, an improved multi-objective particle swarm optimization, which is integrated with the niche technology, is established for the characteristics of multi-objective, multi-constraint during the design process of wind turbine blade layers. Calculation results of the testing functions show that it has strong multi-objective optimization capability and can be used as a optimal design tool for wind turbine blade layers.Secondly, the relationship between actual blade layers and the structural characteristics of blade are built and tested. Test results show that using the PreLayers and PreComp together for computing the blade structural properties is feasible. In addition, computed results by using the curve relationship to express the blade stiffness distribution are closer to the experimental values than using the linear relationship. This has some instructive for setting up the blade finite element model in the future. Then the influence of the blade layers parameters on the sectional stiffness and its reason are analyzed. The researches show that without increasing the sectional mass-line-density, the bigger of the sectional thick of the position at which the layers locate, the greater contribution for the flapwise stiffness. This conclusion provides guidance for the blade stiffness design.Thirdly, a blade natural frequency calculating model and a mass calculating model, which are integrated with the PreLayers and PreComp software, are built by programming and verified. Then the influence of the blade layers parameters on the first-order flapwise frequency are analyzed. The results show that the blade layers moving toward the blade root will improve the first-order flapwise frequency without increasing the blade mass. It provides guidance for the blade frequency design.Fourthly, the reasons for generating the extreme loads are analyzed. A theoretical boundary curve equation between the normal force coefficient Cn and the attack angle a is set up when the attack angle is at the range of0.0to90.0degree. Some new demands are put forward for designing low-load airfoils. In addition, the relationships of wind turbine parameters with the inflow angle and the inflow angle are obtained when the local blade tip speed ratio (TSR) is bigger (λr≥4). And there is a conclusion that the inflow velocity V0will be closer to Ωr while the local TSR becomes bigger. Through the further analysis, another conclusion, which is that the augment of rotor speed will easier produce the extreme load compared with the augment of Cn, is gotten. According to it, some requirements are proposed to control the extreme load. Then, based on the above researching and analyzing results, combined with the improved PSO algorithm, a new extreme load prediction model ELPM is developed. The computation results show that, ELPM can be used to predict the exteme loads for wind turbine blades. Finally, according to the extreme loads from the ELPM, a simple and reasonable method for calculating the maximum blade tip deflection and the ultimate strength is given.Fifthly, based on the above research results, a wind turbine blade layers optimization design model under extreme loads is eventually established. In this model, PreLayers can build the parametric modeling for different blades; free variables, objective function and constraints can be changes according to different design objectives and requirements; and this model can consider most of the design requirements, such as mass, frequency, maximum blade tip deflection, ultimate strength requirements and so on. Results from applicating this model show that this model can be used in different blades for designing blade layers.