Hi,

I am modeling the NREL 5-MW wind turbine in Abaqus/CAE. The blades are generated using the properties of different sections of the airfoils that were considered the same as ref. [1]. Table 2-1 in ref. [1] lists the distributed blade structural properties of the NREL offshore 5-MW baseline wind turbine. The stiffness and orientation of the principal elastic axes can vary for different cross-sections along the length of a blade, depending on the blade geometry.

For the blade properties, 49 stations along the span of the blades were considered. A generalized section is used for different elements of each blade. The properties of this generalized section consisted of the area (A), the moment of inertia along two axes (I11, I22), and polar moment of inertia (J). The material used for blades has an elastic modulus of 13.1 GPa, and shear modulus of 8 GPa according to ref. [2]. The mass of blades is given as longitudinal mass in line with the blade elements.

The strong axis of the blades is oriented at the edgewise direction of the blades. The flapwise and edgewise section stiffness and inertia values, are given about the principal structural axes of each cross-section as oriented by the structural-twist angle (StrcTwst) [1]. Each of the 49 elements of each blade is given a change of angle based on the value of StrcTwst. In fact, elements twist along the blade span from 13.308° at the blade root to 0° at the blade tip.

The Abaqus program handling the structural simulation requires following parameters for a generalized section:

A, I11, I12, I22, J.

To my understanding, the required values from the reference are calculated as follows.

A = EAStff / E

I11 = FlpStff / E

I12 = Null*

I22 = EdgStff / E

J = GJStff / G

Density = BMassDen / Area

- According to “Moments of Inertia” rules, the value of I12 must satisfy the inequality –(I11+I22)/2 < I12 <= (I11+I22)/2.

where A is area (m^2), E is elastic modulus ¶, I11 is the area moment of inertia for the flapwise (m^4), I12 is the area moment of inertia with respect to flapwise and edgewise (m^4), I22 is the area moment of inertia for the edgewise (m^4), J is polar moment of inertia (m^4), Density is the density of each element (kg/m^3).

It seems that the definition of two equations, FlpStff and EdgStff, has been mistaken in ref. [3]. So both formulas have the same x^2 expressions.

FlpStff = ∫∫ E(x, y) x^2 dxdy

EdgStff = ∫∫ E(x, y) x^2 dxdy

where E(x,y) is the modulus of elasticity in N/m^2, and x and y are the flapwise and edgewise distances in meters from the blade section elastic center to the differential area element, respectively.

Nevertheless, it seems that the FlpStff is the bending stiffness about the principal elastic x-axis, and the EdgStff is the bending stiffness about the principal elastic y-axis. According to this definition, values FlpStff and EdgStff are calculated as follows:

FlpStff = ∫∫ E(x, y) y^2 dxdy

EdgStff = ∫∫ E(x, y) x^2 dxdy

where x and y are the edgewise and flapwise distances in meters from the blade section elastic center to the differential area element, respectively.

Is my interpretation of wind turbine blade modeling correct? If my interpretation is correct, do the parameters displayed in Table 2-1 in ref. [1] need to be modified?

Regards,