Adaptive Bend-Torsional Coupling Wind Turbine Blade Design Imitating the Topology Structure of Natural Plant Leaves

In the wind turbine system, the size of the blade is determined by the level of single output power. With the rise of offshore wind turbines (Breton & Moe, 2009), the output power of commercial blade has reached 5MW, and the length of the blade is over 100m. The design and manufacture limit of large-scale wind turbine is facing severe challenges, and as a result, wind turbine blade has become a research focus of scholars from all over the world. In a poor working environment, the problems of large blades in the following two aspects, which occur in the process of operation, will become more and more prominent. 1. In the operation, the blade should bear a good rigidity in order to minimize the destruction that random wind load and gust may cause to the blade (Bishop et al, 1999). Knut (1999) points out that due to the increasing length of wind turbine blade, the blade becomes more vulnerable to the unpredictable destruction caused by random gusts and ultimate wind load. And since the fatigue test of the blade has its limitations, therefore, he proposed a kind of random probability model based on bad working conditions to predict the fatigue life and reliability of the series of blades (Ronold & Larsen, 2000). Christoph (2006) points out that the length and weight of large-scale blade have an increasing impact on the bending load withstood internally. Meanwhile, it becomes more and more difficult for the large blades, which are subjected to wind, rain, moisture, and other adverse environmental effects, to meet the design requirements of a 20-year basic fatigue life. In order to predict the fatigue life of blade more accurately, apart from the unidirectional fiber, he has also made some research on the S-N curve of the off-axis fiber which bears the shear load. In addition, the research on the blade fatigue and damage mechanism has also been attached importance to by domestic and foreign researchers. For example, Daniel (2008), Raif (2008) and other scholars have delved into the fatigue and destruction data and the interlayer destruction mechanism of glass fiber and carbon fiber. They point out that both the technology of blade fiber manufacture and the adaptability of the blade have an important impact on the fatigue and destruction of the blade. Thus with the wind turbine blade becoming lager and larger, it becomes more and more difficult to maintain the rigidity of the blade. Even within the rated wind speed, the instability of the wind speed produces a serious varied load to the blade, increasing the