This paper presents a recently developed numerical multidisciplinary optimization method for design of wind turbine blade. The objective was the highest possible blade weight under specified atmospheric conditions, determined by the design giving girder layer and location parameter. Wind turbine blade on boxsection beams girder is calculated by ply thickness, main girder and trailing edge. In this study, a realistic 30 m blade from a 1.2 MW wind turbine model of blade girder parameters is established. The optimization evolves a structure which transforms along the length of the blade, changing from a design with spar caps at the maximum thickness and a trailing edge mass to a design with spar caps toward the tip. In addition, the crosssection structural properties and the modal characteristics of a 62 m rotor blade were predicted by the developed beam finite element. In summary, these findings indicate that the conventional structural layout of a wind turbine blade is suboptimal under the static load conditions, suggesting an opportunity to reduce blade weight and cost.
As wind turbines continue to grow in size, it becomes increasingly important to ensure that they are as structurally efficient as possible to ensure that wind energy can be a costeffective source of power generation. Aerodynamic and structural optimization has become a subject of considerable interest. It involves the determination of the geometry of an aerodynamic configuration that satisfies certain objectives subject to constraints [
The shape of wind turbine blades is complicated. The main bearing structure of blade is the main girder of the blade; the structure design of the main girder is a key part of the blade design. Composite material structure design generally uses allowable strain design.
The structural design of the blade mainly includes two aspects; one is the section of the blade structure; the other is section layer material selection and arrangement and calculating the thickness of layers. The main girder structure of large wind turbine blades is mainly double shear web girder or box girder at present [
The considered blade is made of composite materials containing more than one bonded material, each with different structural properties.
Figure
Crosssection of blade.
The skin and the shear web thickness should be given before the thickness of the main girder of blade; skin is mainly laid bidirectional cloth and bidirectional cloth is mainly used to bear the torque, but actually the torque is borne by blade, small thickness given in [
From the above equations,
Front curvature is larger and main girder bending ability is stronger, so it assumes that front and main girder buckling instability does not occur. The airfoil trailing edge of the blade section is generally wider and its curvature is small; it is easy to have an instability problem. In order to enhance its stiffness, it lays this sandwich layer; generally the trailing edge of the blade profile is assumed as plate to calculate the antibuckling thickness. The trailing edge is simplified as flat as shown in Figure
Schematic diagram of area element at trailing edge.
Corresponding to calculation formula (
Where
Substituting (
It is not possible to formulate the problem of optimum design of wind turbine blades as a singlecriterion optimisation task because this process requires many criteria to be taken into account. Blade design is here performed with a constrained optimizationbased procedure. In formulating an optimization problem, three principal phases must be considered [
definition and measure of design objectives,
choice of the design variables and preassigned parameters,
definition of the design constraints.
The blade profile structure is shown in Figure
The objective function is linear density of blade mass. Based on the study of [
In order to decrease dimensionality of the optimization problem, some of the variables are preassigned fixed values. They are (a) layout parameters including blade length, chord, twist, and precone and (b) crosssectional parameters including airfoil type and dimensions of internal webs and covering skin. The design variables, which are subject to change in the optimization process, are chosen to be the dimensionless radius of gyration, crosssectional area, and length of each segment composing the main blade spar [
For thinwalled sections with constant, if the profile is discrete, blade sectional area of the first
Finally, it can be expressed as follows:
After having carried out the study of formulating an optimisation criterion when minimising quality, all design requirements are treated as constraints; therefore, all converged solutions are viable according to the conditions that have been imposed by the designer. The code performs the design using a multilevel approach. Considering blades as double shear webs, it will be meaningless if the distance from anterior shear web to front end, the initial position of main girder along crosssection chord of blade which is the location
From the above equations,
The values of
In this study, a megawatt wind turbine blade will be computed layer and the placement parameters of the main girder will be optimized by genetic algorithm. When it is programmed with genetic algorithm, MATLAB genetic algorithm toolbox which is made up by Sheffield University swill be used. Genetic algorithm parameters are as follows: the population size is 280, the maximum algebra of evolution is 470, variable dimension is 2, and crossover rate is 0.35.
Optimisation calculations were done with the use of the thors program that implemented a modified genetic algorithm for which the following assumptions were made. The specific results are shown in Table
Parameters comparison after optimization.
Parameters  Before optimization  After optimization 


0.2  0.2146 

0.2  0.1728 

2.35 
2.77 

1.84 
1.71 
Mass per unit length comparison after optimization.
Leading edge layer thickness.
Spar cap layer thickness.
Trailing edge layer thickness.
It is not convenient to consider the blade root when it is calculated, so it must be designed separately. Table
As illustrated in Figure
As can be seen in Figure
Figure
The layer depth value of girder section near the blade root is very large, which causes error according to the committee airfoil calculation given; the actual blade in the transition section profile by is changed airfoils to round shape.
We presented our latest developments toward a direct design method for HAWTs. The design method was based on numerical optimization and several calculation models: aerodynamic calculations and structural calculations. An optimization model is developed by constraining blade stiffness, taking minimum quality of blade as the objective function, and calculating the parameters of main girder of blade with genetic algorithm. By optimizing calculations, the position of the main girder of blade shifts toward the rear edge and its width increases somewhat. The synergistic use of fiber rotations in the skin and spar caps is beneficial in terms of blade weight. In fact, fiber rotations in the skin allow one to limit rotations in the spar caps. The multidisciplinary optimization model is found to be appropriate and efficient in arriving at optimum blade designs and identifying useful design trends with various design specifications.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors would like to acknowledge the financial support made available through the Natural Science Foundation (no. 51165019), the Natural Science Foundation of GANSU Province (no. 1308RJYA018), and the Fundamental Research Funds for the Lanzhou city technology bureau projects (no. 20134110). These supports are gratefully acknowledged.