Main shaft

The main shaft is the principal part of the power train connecting the rotor with the gearbox or directly the generator. The Main shaft has two bearings connecting it to the Nacelle frame - the front and aft bearings. The bearings let the main shaft spin freely. The bearings are positioned along the main shaft using relative parameters.

The main shaft is rotated by the aerodynamic torque on the rotor, whereas the generator applies a braking torque (in the opposite direction). 

If there is no gearbox, then the power train (transmission) is called direct drive. Thus, the parameter Transmission in the RNA part has the two options: Geared and Direct drive. In a geared drivetrain, the main shaft is also called low speed shaft and the shaft connecting the gearbox and the generator the high speed shaft. Due to the gearbox, the highspeed shaft is indeed rotating much faster thatn the lowspeedshaft, typically with a factor or around 100. The generator in a geared WT typically has a rated RPM of 1000-2000 rpm.

Geometry

Scaling scheme

Scheme for scaling of this part only.


Options:

Parent (default):

The scale factor is set equal to the scale factor for the parent part.

Override:

A scaling factor (set by you) for this part only (i.e. the scaling factor set for the parent part is overridden).

Scaling factor

The geometry of this part will be scaled by this factor.


  • Default value: 1
  • Unit: —
  • Range: 0.001 — 1000

Length

The length of the main shaft (distance along the shaft from the end to the hub center).


  • Default value: 10
  • Unit: $\text{m}$
  • Range: 0.001 — 100

Hori. distance to hub

The horizontal distance from the tower top (i.e. yaw axis) to the hub (i.e. the front of the main shaft).


  • Default value: 5
  • Unit: $\text{m}$
  • Range: 0 — 100

Vert. distance to hub

The vertical distance from the tower top (i.e. yaw axis) to the hub (i.e. the front of the main shaft).


  • Default value: 2.4
  • Unit: $\text{m}$
  • Range: 0 — 100

Maximum element length

The maximum length a generated frame element of the main shaft can have, i.e. the elements will have this length or shorter.


  • Default value: 2
  • Unit: $\text{m}$
  • Range: 0.01 — 100

Cross section

Shaft radius

Outer radius of the main shaft.


  • Default value: 0.8
  • Unit: $\text{m}$
  • Range: 0.005 — 10

Wall thickness

The thickness of the shaft walls.


  • Default value: 0.028
  • Unit: $\text{m}$
  • Range: 0.001 — 1

Shaft material

The name of material to use for the cross section.

  • Default value: SteelMassless
  • Unit: —

Advanced

Front bearing position

The relative position of the front bearing along the main shaft, given as a fraction of the main shaft length. That is, a value of 0 means at the hub center, while a value of 0.9 means 10% from the aft of the main shaft.


  • Default value: 0.1912
  • Unit: —
  • Range: 0 — 0.9

Aft bearing position

The relative position of the aft bearing along the main shaft, given as a fraction of the main shaft length. That is, a value of 0.1 means a tenth from the hub center, while a value of 1 means at the aft of the main shaft.

The aft position must be at least 0.1 greater than the front position. If it is not then it will be auto-adjusted.

  • Default value: 0.8
  • Unit: —
  • Range: 0.1 — 1

Bearings locked

If enabled, the two bearings will be locked; i.e. the shaft will be rigidly connected to the nacelle. The shaft will not be able to rotate. In an eigenvalue analysis, this option will always be enabled.

If the bearings are locked then the initial RPM (rotational velocity) of the rotor and generato will be set to 0 by changing Analysis parameters-> Initial conditions-> RPM to 0 rpm, and RPM, TSR, or Tip speed to Specify RPM, and disabling both parameters.

  • Default value: False
  • Unit: —