Mass and Static Inertia

The MassProperties must represent the combined mass of the drivetrain (shafts, bearings, gearbox) and the nacelle, including the mass of the generator. The inertia term should include only the static components of the drivetrain and nacelle and exclude rotational inertia of components such as the low-speed shaft, high-speed shaft, slipping clutch (if any) and generator inertia. See rotational inertia of the drivetrain for more about rotational inertia definition options. The mass and static inertia of the Yaw System is also a part of MassProperties. Table 1 presents and overview of what is included in MassProperties.

Note

If a gearbox mounting flexibility is added, then include the static moment of inertia about the x-axis there and not in the nacelle inertia.

Table 1: A table showing whether a components mass and static inertia is included in MassProperties.

Component	Mass and static inertia part of DrivetrainAndNacelle::MassProperties?
Gearbox	Yes
Generator	Yes
Low-Speed Shaft	Yes
High-Speed Shaft	Yes
Slipping Clutch	Yes
Yaw System	Yes
Hub	No
Tower	No

As the DrivetrainAndNacelle component is often either attached to the distal node of the Tower, YawSystem, TranslationObject or RotationalObject, the coordinate system used for the definition depends on the orientation of their distal nodes, see Figure 1. For downwind configured turbines the body-fixed frame of the DrivetrainAndNacelle is rotated 180 degrees, which effectively rotates the coordinate system used to define the CentreOfGravity and MomentOfInertia properties. Thus the user does not need to change the properties when changing between upwind and downwind configurations.

Figure 1: Diagram illustrating the Centre Of Gravity (CoG) position in the proximal coordinate system of the DrivetrainAndNacelle component. Shown for an upwind configured turbine.

The properties of the MassProperties are:

• CentreOfGravity: The x, y, z components of the centre of gravity of the nacelle and all of its contents. This is measured relative to the component's origin, see Figure 1.
• MomentOfInertia: The total moment of inertias of the nacelle and all of its contents. Yawing being about the Z-axis, Nodding about Y-axis and Rolling about the X-axis, see Figure 1.

Example of a populated MassProperties data:

"MassProperties": {
    "TotalMass": 229160.0,
    "CentreOfGravity": {
        "X": -1.52,
        "Y": -0.932,
        "Z": 1.42
    },
    "MomentOfInertia": {
        "Yawing": 5043178.0,
        "Nodding": 3765374.0,
        "Rolling": 1134132.0
    }
}