*BLADE STRUCTURE |
 
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*BLADE STRUCTURE |
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To specify the structural properties of wind turbine blades.
Please note that if you are using the rigid blade model, the blade geometries are approximated as rigid profiles. This means that the *BLADE STRUCTURE keyword inputs are irrelevant. If you are using the flexible blade model, the rotor nacelle assemble (RNA) is explicitly modelled using finite elements, thereby allowing blade deformations and rotational inertia to be accurately captured.
Refer to Turbine Geometry for further information.
A block of lines starting with the blade name, followed by as many lines as necessary to completely define the blade structural properties as a function of fractional distance along each blade. The entire block of data may then be repeated for other blades.
Line defining the blade name:
BLADE NAME=Blade Name
Line defining the blade structural properties at a particular value of fractional distance along the blade (this line may be repeated as often as required):
Blade Fractional Distance, Pitch Axis, Structural Twist angle, Section Mass, Flapwise Stiffness, Edgewise Stiffness, Torsional Stiffness, Extensional Stiffness
Refer to the Blade Geometry schematics for an illustration of the various inputs. Each blade definition must have properties defined for at least two values of blade fractional distance. The Blade Fractional Distance entries must be entered in monotonically increasing order, from the most inboard to the most outboard. The first entry must be 0.0 and the last entry must be 1.0.
The rotor is assembled according to the blade selections and related information defined in the *TURBINE ROTOR keyword. Flexcom creates a node in the finite element discretisation corresponding to each blade span position defined in the *BLADE GEOMETRY keyword. These nodes are connected sequentially using finite elements whose structural properties are governed by the inputs in the *BLADE STRUCTURE keyword. The structural properties are assumed constant along each element, and determined using linear interpolation between the element centrepoint and the nearest available sectional definitions.
Input: |
Description |
Blade Name: |
The name of the blade. Note that the same blade names should be used in the *BLADE GEOMETRY, *BLADE STRUCTURE and *TURBINE ROTOR keywords. |
Blade Fractional Distance: |
The fractional distance of the blade along the blade pitch axis. Values must vary from 0 to 1. The first distance corresponds to the blade root and must have a value of 0. The last distance, which corresponds to the blade tip, must have a value of 1. |
Pitch Axis: |
This input is used to locate the aerodynamic center of the corresponding airfoil section. Sometimes referred to as "AeroCent" in OpenFAST notation, it represents the fractional distance along the chordline from the leading to the trailing edge, where it is assumed that pitch axis passes through the airfoil section at 25% chord so that the leading edge is 25% ahead of the pitch axis along the chordline and the trailing edge is 75% aft of the pitch axis along the chordline. The input is limited to values between 0.0 and 1.0. A value of 0.0 corresponds to the leading edge, a value of 0.25 corresponds to the blade pitch axis, and a value of 1.0 corresponds to the trailing edge. Refer to OpenFAST documentation for further details. |
Structural Twist Angle: |
The orientation of the principal axis. It must be greater than -180 and less or equal than 180 degrees. |
Section Mass: |
The blade section mass per unit length. |
Flapwise Stiffness: |
The blade section bending stiffness in the flapwise direction. |
Edgewise Stiffness: |
The blade section bending stiffness in the edgewise direction. |
Torsional Stiffness: |
The blade section torsional stiffness. |
Extensional Stiffness: |
The blade section axial stiffness. |
(a)You can define as many blades as you wish in the *BLADE GEOMETRY and *BLADE STRUCTURE keywords. Only the blades which you reference in the *TURBINE ROTOR keyword will be used in the model.
(b)Flexcom creates a node in the finite element discretisation corresponding to each blade span position defined in the *BLADE GEOMETRY keyword. These nodes are connected sequentially using finite elements whose structural properties are governed by the inputs in the *BLADE STRUCTURE keyword. The structural properties are assumed constant along each element, and determined using linear interpolation between the element centrepoint and the nearest available sectional definitions.