Structure Design Of Composite Wind Turbine Blade

The blade is one of the most important parts and more complicated load for wind turbine. Based on better designed blade, higher power coefficient is obtained and better economic profit can be gained. Considered the operate characters of the wind turbine and the advantages of composite material with high strength, low density, corrosion resistant and so on, fiber reinforced composites is the main material of blade. However, the design of composite wind turbine blade must be based on the strong theory to ensure that the structure design is feasible, rational and economical.The micromechanics Bridging Model constitutive theory of composite materials, was fully considered the impact of the nonlinear characteristic of matrix material on structural strength. And the theory was incorporated with finite element software ABAQUS through a user subroutine UGENS to analyze the progressive failure process and ultimate strength of a composite wind turbine blade, which has a complicated three-dimensional geometry. Under the input of the constituent fiber and matrix properties, fiber volume fraction, and skin and rib lamination parameters such as lamination angle, thickness and number of laminas used, the software was able to estimate the overall load-carrying capacity of the wind turbine blade and to locate the position where the blade ultimate failure was taken place. Based on this, the composite wind blade structure can be effectively evaluated, and an optimization in structural design can be achieved easily.The thus developed method has been applied to the particular lamina design, stiffness and strength analysis, the overall load-carrying capacity calculation, the ultimate failure analysis natural frequency calculation and stability analysis of a 20kW and 660kW composite wind turbine blade. Simultaneity, a 660kW composite wind turbine blade with two structures was designed and analyzed. One of is hollow core structure, and another is foam core structure. Strength, rigidity and natural frequency and stability of two structures had been analyzed, and for each blade cross-section of above two structures, unit blade mass, flap stiffness, lag stiffness, torsion stiffness and axial stiffness, reflecting mechanical parameter of blade structural properties, were calculated by Precomp a free code program which was developed by NREL specially for computation of composite blade structural properties. Compared the mechanics parameter, we can distinguish the strong points and disadvantages of the two structures.The thus developed method has been applied to the design and analysis of the composite wind turbine blade with an advanced structure, and favorable results with improved strength and stiffness and reduced weight have been obtained. This method is also well applicable to the ultimate failure analysis and strength design of other complicated composite structures.