Blade Section Properties

Property Coordinate Systems

There are three categories of properties applicable to each blade section: StructuralProperties, MassProperties, and AerodynamicProperties. Each property is defined relative to an origin and often includes orientation information, such as bending stiffnesses about X and Y axes. Consequently, this leads to the establishment of four property coordinate systems, each associated with one of the three property groups outlined in Table 1.

Table 1: List of blade section coordinate systems

Property Group	Coordinate System Name	Origin	Orientation
StructuralProperties	NeutralAxisCoordinateSystem	The neutral axis of the section	The principal bending axes
StructuralProperties	ShearAxis	The shear centre of the section	There is no orientation for the ShearAxis
MassProperties	MassCoordinateSystem	The centre of gravity of the section	The mass principal axes
AerodynamicProperties	QuarterChordCoordinateSystem	The quarter-chord position, located 1/4 of the way along the chord-line	The Y-axis will point from the leading edge to the trailing edge

Figure 1: Blade section property coordinate systems.

Transformation From Reference System to Property System

The XY plane of the reference coordinate system defines the plane in which all of the section's properties are defined. The other coordinate systems and loci are defined in the reference XY plane, but with an optional rotation about reference \(Z_{ref}\) axis and a subsequent (also optional) translation in the reference \(X_{ref}\) or \(Y_{ref}\) systems. Both transformations occur in the reference system, such that the rotation and subsequent translation are decoupled (i.e. you can change the rotation without affecting the position, and vice-versa). This is illustrated in the animation below.

Figure 2: Transformation from reference system to property system.

Each of the property coordinate systems have the following properties:

Table 2: Common coordinate transformations from the section reference system

Property	units	Description	Default
RotationAboutReferenceZ	radians	The rotation - following the right-hand convention - of the coordinate system about the reference \(Z_{ref}\) axis before translation	0.0
OffsetInReferenceX	meters	The X position of the property axis origin in the reference coordinate system	0.0
OffsetInReferenceY	meters	The Y position of the property axis origin in the reference coordinate system	0.0

If any single property is omitted, it will default to 0.0. If the entire section is omitted for one of the coordinate systems, then all of these values will remain at their default value of 0.0 - meaning that the coordinate system will be coincident with the reference coordinate system.

All four property systems are transformed from the reference system in a similar manner.

Figure 3: Blade section reference coordinate system.

As all of the property coordinate systems are defined in terms of the reference coordinate system, if the reference coordinate system is moved or rotated (by modifying its Origin, ZAxis or YAxis), then all of the property coordinate systems will move and rotate with it.

Figure 4: Moving the blade section reference coordinate system.

Overview of Coordinate System Names and Property Groups

Table 3: List of coordinate systems` and their properties

Coordinate System Name	Associated Property Group	Associated Properties in Group
NeutralAxisCoordinateSystem	StructuralProperties	BendingStiffnessAboutX
		BendingStiffnessAboutY
		AxialStiffness
		ShearStiffnesses
		CouplingTerms
ShearAxis	StructuralProperties	TorsionalStiffness
QuarterChordCoordinateSystem	AerodynamicProperties	Chord
		ThicknessToChordRatio
		AerodynamicSection
MassCoordinateSystem	MassProperties	MassPerUnitLength
		MomentOfInertia
		RadiusOfGyration

Any of these properties or property groups can be omitted with the exception of the AerodynamicProperties and its three properties, which are required to define the section's aerodynamic behaviour.

Where a stiffness is omitted, Bladed will assume that it is rigid in that degree of freedom. If the entire StructuralProperties group is missing, then it will model it as rigid.

Warning

In the current implementation, any given stiffness must be provided for the entire blade or none of it. This means that you can't have a rigid element on an otherwise flexible blade, or vice versa.

Note

To set a given degree of freedom to be rigid, you can search for the respective keyword and replace it with an underscored version: for example, to make the blade rigid in extension, replace all "AxialStiffness" with _AxialStiffness.