S

Rotational Inertia of the Drivetrain

There are several ways of specifying the rotational inertia of the DrivetrainAndNacelle (see mass and inertia for static inertia and mass inputs).

The GearboxInertia, in the context of drivetrains without a Slipping Clutch, represents the total rotational inertia of the drivetrain excluding the GeneratorInertia. The GearboxInertia refers to the high-speed side of the gearbox, but also accounts for the low-speed shaft if the gear ratio is factored in during the inertia summation. Alternatively, users have the option to specify the inertia of the low-speed shaft as part of the Hub's MomentOfInertiaAboutShaft property, resulting in an equivalent outcome. See Figure 1 for illustration of the options and Table 1 for an overview of the inputs.

Table 1: Location of rotational inertia inputs

Component	Rotational Inertia Input
Gearbox	DrivetrainAndNacelle::GearboxInertia
Generator	VariableSpeedGenerator::GeneratorInertia
Low-Speed Shaft	DrivetrainAndNacelle::GearboxInertia or Hub::MassProperties::MomentOfInertiaAboutShaft
High-Speed Shaft	DrivetrainAndNacelle::GearboxInertia or if SlippingClutch then: SlippingClutch::HighSpeedShaftInertia
Slipping Clutch	SlippingClutch::HighSpeedShaftInertia
Hub	Hub::MassProperties::MomentOfInertiaAboutShaft

Figure 1: Illustration of a drivetrain without a slipping clutch and how the different rotational inertias are applied. Note that the GearboxInertia includes the low-speed shaft, but could alternatively been made a part of the hub's MomentOfInertiaAboutShaft property.

The high-speed shaft divides into two segments when a Slipping Clutch is introduced. Consequently, it becomes necessary to define the inertia of the high-speed shaft up to the slipping clutch using the property: HighSpeedShaftInertia. The inertia from the slipping clutch to the generator would then be part of the GeneratorInertia. This illustrated in Figure 2.

Figure 2: Illustration of a drivetrain with a slipping clutch and how the different rotational inertias are applied.