This website uses local storage to ensure you get the best experience on our website.

Table of Contents

Flexible Geared Yaw Bearing

Bladed provides the facility for users to model a flexible geared yaw bearing in single rotor turbines (not compatible with multi-rotor). This is modelled within the Bladed multibody structural model. This functionality is activated via a new module written into Project Info.

This feature works for turbines with both upwind and downwind rotor nacelle assembly configurations.

Description of Yaw Bearing

The flexible geared yaw bearing is modelled with a yaw gearbox mounted in the nacelle. The component is inserted between the tower top and yaw bearing nodes denoted “TT” and “YB” respectively. Multibody diagrams of the system are presented below.

The gearbox has a single rotational degree of freedom and has a fixed gear ratio between the low-speed shaft (LSS) and the high-speed shaft (HSS). There are three options for representing the connection between HSS and motor inertia:

  1. A rigid HSS with a single concentrated inertia (see Figure 1),

  2. A torsional flexible HSS with a single concentrated inertia (see Figure 1), and

  3. Two torsional flexible HSS each with separate inertias (see Figure 2).

The total inertia of the yaw drives can be represented by either a single inertia or can be represented by two inertias if defining separate load banks. The actuator torque should be applied to the “YBH” nodes and “YBH2” node (if more than one load bank is specified) as denoted on the diagram. More instructions are provided below. The yaw gearbox includes viscous damping and constant friction terms where the coefficients can be specified by the user. The LSS is connected to the tower via a torsional flexibility characterised by rotational stiffness and damping values again specified by the user.

Single Bank MB diagram

Figure 1: Multibody diagram for geared yaw bearing with and without high-speed shaft (HSS) flexibility.

Dual Bank MB diagram

Figure 2: Multibody tree for flexible geared yaw bearing with 2 load banks.

Defining the Yaw Bearing

Yaw Bearing Definition

The full definition of the yaw bearing input options are shown in the following Project Info code.

MSTART FLEXGEARYAWSYS
UseFlexGearedYawSystem   1   * Switches the functionality on
NumberOfLoadBanks   2 * (Optional) Indicates the number of yaw actuators
JmotorTotal     0.1, 0.1 * Total inertia (kg·m^2) of each actuator (If NumberOfLoadBanks=2, then 2
values are needed.)
GearboxRatio    10000.0 *Gearbox speed ratio
YawStiffness    3.0e9 (N·m/rad) *Torsional stiffness of Yaw flexibility component
YawDamping  7.0e7 (N·m/(rad/s)) *Torsional damping of Yaw flexibility component
GearBoxDamping  1.0e5 (N·m/(rad/s)) *Coefficient of damping/viscous friction for gearbox
GearBoxFriction 1.0e5 (N·m) *Constant rotational friction torque expressed as 
equivalent friction on the low-speed side.
LockGearbox 1  *Flag to lock the gearbox (0=unlocked, 1=locked)
ActTorqueLinPerturb 0.001 (N·m) (Optional) *Yaw actuator torque perturbation for model linearization. 
(If NumberOfLoadBanks=2 then half of the perturbation torque is applied to each actuator).
IncludeHssFlexibility   Y   *Include/Exclude HSS flexibility (if NumberOfLoadBanks=2, then 
IncludeHssFlexibility needs to be set to “Y”)
GearBoxInertia  0.1 (kg·m^2)  *Moment of inertia of gearbox (referred to high-speed side)  
HSSStiffness    1.0e6, 1.0e6 (N·m/rad)  *Torsional stiffness of High-Speed Shaft (HSS) of each load bank 
(If NumberOfLoadBanks=2, then 2 values are needed.)
HSSDamping  1.0e6, 1.0e6 (N·m/(rad / s))  *Torsional stiffness of High-Speed Shaft (HSS) of each load bank 
(If NumberOfLoadBanks=2, then 2 values are needed.)
MEND

Notes:

  1. If the turbine is multi-rotor then a flexible geared yaw bearing option cannot be used.

  2. Number of actuator load banks is defined by NumberOfLoadBanks. This parameter could be 1 or 2. The number of required values for JmotorTotal, HSSStiffness, and HSSDamping is equal to the value of NumberOfLoadBanks. If NumberOfLoadBanks=2, then user needs to define 2 values for those three parameters.

  3. The inertia of the actuators of each load bank is lumped into the input JmotorTotal for that load bank. This value comprises the inertia of one motor in a load bank, times the numbers of drives in that load bank.

  4. The GearboxRatio represents the total gear ratio from the actuator motor to the pinion & ring gear contact point.

  5. The parameter ActTorqueLinPerturb is optional and only used when carrying out model linearization. It corresponds to the maximum perturbation applied to the yaw actuators to obtain the dynamical response in the linear regime. It must be non-zero. If there are 2 yaw actuators, then half of the perturbation torque applied to each of them.

  6. If NumberOfLoadBanks=2, then IncludeHssFlexibility needs to be set as "Y”.

  7. If HSS flexibility is switched on, by setting IncludeHssFlexibility as “Y”, then values of GearBoxInertia, HSSStiffness, and HSSDamping are required. Note: these values should be positive (greater than zero).

  8. For time-domain simulations the initial yaw position (or gearbox position) cannot be modified and is always 0 degrees. An angle of 0 deg means the rotor is pointing Northwards/Southwards in upwind/downwind turbine configurations respectively.

Interactions with Yaw Control Options in UI

Switching on this functionality disables yaw control options that the user can specify in the user interface (UI) under Control > Yaw control. When UseFlexGearedYawSystem=1, Bladed overrides the user’s input in the Yaw Control window by setting Yaw Dynamics and Active Yaw to None. A warning is issued to the user. The initial nacelle angle specified under Calculation Parameters > Initial Conditions is also inactive in this case.

Logging

A Logging group is created for the flexible geared yaw bearing model. It contains the following series:

  • Gearbox position – Yaw gearbox rotation angle wrapped to \([-\pi, \pi)\). Angle of 0 deg means the rotor is pointing Northwards/Southwards in upwind/downwind turbine configurations respectively. Angle is measured anticlockwise (looking down onto the turbine) relative to North.
  • Gearbox rate – Yaw gearbox rotation angle rate.
  • LSS flexible hinge position – Angular deflection of yaw bearing low-speed shaft. Angle wrapped to \([-\pi, \pi)\).
  • LSS flexible hinge rate – Angular deflection rate of yaw bearing low-speed shaft.
  • HSS flexible hinge position – Angular deflection of high-speed shaft. Output depends on inclusion of high-speed shaft flexibility. Angle wrapped to \([-\pi, \pi)\). Will be numbered if more than one high-speed shaft is included.
  • HSS flexible hinge rate – Angular deflection rate of high-speed shaft. Output depends on inclusion of high-speed shaft flexibility. Will be numbered if more than one high-speed shaft is included.
  • Motor position - The gearbox position multiplied by the gearbox ratio. If HSS flexible component is included then the motor position of each load bank is the sum of the gearbox position multiplied by the gear ratio and HSS flexible hinge position of the corresponding load bank. Angle wrapped to \([-\pi, \pi)\).
  • Motor rate - The gearbox rate multiplied by the gearbox ratio. If HSS flexible component is included then the motor rate of each load bank is summation of the gearbox rate multiplied by the gear ratio and the HSS flexible hinge rate of the corresponding load bank.

The positions and rates are reported relative to the tower top coordinate system where the yaw bearing attaches to the structure.

Controlling the Yaw Bearing

The flexible geared yaw bearing can be controlled via the external loads DLL. Torque(s) can be applied to the nodes "YBH" (and "YBH2" if more than one load bank is specified) using the function:

ApplyMultibodyNodeTorqueInLocalFrame(const std::string& node_id, 
const std::string& component_id, 
const GHExternalLoads::DOF3& applied_torque)

To apply a torque to the "YBH" node the function arguments should be specified as:

  1. node_id=”YBH” is the name of the proximal node of the “Yaw Motor Inertia” component;

  2. component_id=”Yaw Motor Inertia”, the name of the component on the side of the node where the torque is applied;

  3. node_id=”YBH2” is the name of the proximal node of the “Yaw Motor Inertia 2” component on the second load bank;

  4. component_id=”Yaw Motor Inertia 2”, the name of the component on the second load bank on the side of the node where the torque is applied;

  5. applied_torque is a vector specifying the applied torque on a node. The applied torque must be of the form \((0, 0, M_z)\) where \(M_z\) is the motor torque;

Applying a positive torque results in a positive yaw bearing angle rate and an increased yaw bearing angle.

It is recommended to also apply an equal and opposite reaction torque to where the gearbox casing attaches, e.g. node “YB”

The external loads DLL can communicate with an external controller (written with the application programming interface) via the interface functions GetNamedUserVariable and SetNamedUserVariable. These functions allow the user to read and write a variable named by the user (for instance “YawTorqueInput” or “YawBearingAngle”, respectively). The named user variables are shared between the external loads DLL and the external controller.

Last updated 06-09-2024