Drivetrain Shafts

The two main shafts of the drivetrain are the low-speed shaft and the high-speed shaft. Each is attached to either side of the gearbox. The low-speed shaft connects the hub to the gearbox and the high-speed shaft connects the gearbox to the generator or slipping clutch. This is illustrated by the multibody diagram of the drivetrain.

When using the standard drivetrain modelling options in Bladed the user may incorporate flexibility into the drive shafts. For the low-speed shaft (LSS) both torsional flexibility and transverse bending of the shaft can be defined. For the high-speed shaft only the torsional flexibility can be defined.

Low-Speed Shaft Flexibility

The low-speed shaft has the option to be made flexible in bending and/or in torsion.

Low-speed shaft bending is modelled in Bladed with two rigid massless shafts connected at a hinge, as shown in Figure 1. The point of bending (HingePosition) is entered as a fraction along the shaft length (EffectiveShaftLength) measured from the hub. For example, a HingePosition of 0.0 positions the hinge at the hub. By contrast a HingePosition of 1.0 positions the hinge flexibility is at the gearbox.

The hinged connection is modelled as a 2D hinge, with freedoms \(y\) and \(z\) that are transverse to the shaft rotational \(x\)-axis. The arrangement of nodes is show in a multibody diagram . The transverse BendingStiffness and BendingDamping of the hinged connection should also be entered.

Figure 1: Illustration of the `EffectiveShaftLength` and `HingePosition`.

Low-speed shaft torsional flexibility around the shaft rotational \(x\)-axis is covered by the properties TorsionalStiffness and TorsionalDamping. This is optional and can work in combination with the 2D hinge model effectively making it 3 degree of freedom model.

Note

If flexibility in the high-speed shaft, gearbox, or pallet mounting is not considered, the LSS (Low-Speed Shaft) stiffness parameter should account for the total torsional flexibility between the rotor and the tower top. For most geared transmission configurations, it’s important to account for the combined effects of low-speed shaft flexibility and the equivalent torsional flexibility of the gearbox mounting arrangement. Additionally, consider whether the rotor hub, gearbox low-speed stage, and/or yaw system roll introduce significant additional torsional flexibilities around the low-speed shaft axis.

List of all the available properties of the LowSpeedShaft object:

EffectiveShaftLength: Length of the low-speed shaft considered for the bending model. Measured from the hub centre (ie the LSS distal node) along the LSS axis of rotation, as shown in Figure 1.
HingePosition: Fraction of the EffectiveShaftLength (from the hub centre) where the hinge between the two shafts are connected.
BendingStiffness: The shaft's bending stiffness about any axis perpendicular to the axis of rotation.
BendingDamping: The shaft's bending damping about any axis perpendicular to the axis of rotation.
TorsionalStiffness: The shaft stiffness about the axis of rotation.
TorsionalDamping: The shaft damping about the axis of rotation

Example of a populated LowSpeedShaft object:

"LowSpeedShaft": {
    "EffectiveShaftLength": 3.0,
    "HingePosition": 0.5,
    "BendingStiffness": 2321000.0,
    "BendingDamping": 230000.0,
    "TorsionalStiffness": 160000000.0,
    "TorsionalDamping": 250000.0
},

High-Speed Shaft Flexibility

The torsional flexibility of the high-speed shaft can be defined using the HighSpeedShaftTorsion object, containing these two properties:

TorsionalStiffness: The torsional stiffness of the high-speed shaft
TorsionalDamping: The structural damping about the torsional degree of freedom for the high-speed shaft

Example:

"HighSpeedShaftTorsion": {
    "TorsionalStiffness": 160000000.0,
    "TorsionalDamping": 250000.0
},

Table of Contents

Drivetrain Shafts

Low-Speed Shaft Flexibility

Note

High-Speed Shaft Flexibility