1. Wind turbine specification

This data group is optional and is only available for Arbitrary Systems. It enables the user to model wind turbines considering wind load acting on the blades and control system for blade pitch and electrical power extraction. For normal riser systems this data group should not be considered.

The wind turbine is modelled by a group of lines that constitute the blades and the shaft, see figure `Outline of a wind turbine model' below. In addition, references to the air foil library file and to control data for electrical torque and blade pitch must be given.

A shared supernode at the hub connects the blades and the shaft. Each blade must consist of two lines. The inner line represents eccentricity and the outer line the actual foil blade. A rigid supernode connection is used to represent connection between the two lines. The constant term, c0, in the linear constraint equation is subsequently used for blade pitch control.

The wind turbine blades have to be identical with regard to the element distribution, foil profile description and aerodynamic coefficients along the blades. The mass and stiffness distribution may be different.

The wind loads on the blades are computed based on the load coefficient description in the air foil library file and together with a blade element momentum (BEM) method. The applied BEM code includes dynamic inflow, i.e. a time delay on changes of induced velocity related to the time it takes to convect vorticity in the wake downstream, away from the rotor. With dynamic inflow, the BEM method will give correct time series of rotor and blade loads under conditions of changing blade pitch angle, wind speed and direction, and tower motion. The main features of the BEM theory are:

  • Induced velocity is calculated assuming momentum balance for a ring-shaped control volume.

  • Blade sections are treated as independent.

  • Aerodynamic coefficients from wind tunnel tests are used for the blades.

  • Empirical corrections are used for tip-vortices and cascade effects / lift amplification.

The BEM theory is a proven, simple and CPU efficient method to simulate rotor aerodynamics and the method represents the industry standard. Additional information regarding the coordinate systems for the wind turbine results can be found in Wind Turbine Results.

um ii fig48
Figure 1. Outline of a wind turbine model

Nacelle yaw control is optional, and can be added to a wind turbine through appending an extra line as an extension to the tower top. The yaw correction will be given as a prescribed rotation of the yaw line, relative to the tower top. The tower top (tower line end 2) and end 1 of the yaw line must be located in two different supernodes at the same location.

um ii fig177
Figure 2. Outline of yaw controller model

1.1. Data group identifier, one input line

WIND TURBine SPECification

1.2. Specification of windturbine(s), one input line

NWITURB

  • NWITURB: integer: Number of wind turbines to be specified

There is no limit to the number of wind turbines that can be specified. The dynamic load conditions wind events, shutdown and blade pitch faults can only be used for systems with one turbine.

1.3. Component type identifier

FILE_NAME

  • FILE_NAME: character: Name of the airfoil coefficient library

    • = 'NONE': No file

The airfoil lovrary file is described in Airfoil library file description.

The next input lines are given in one block for each wind turbine.

1.4. Wind turbine identifier, one input line

WIND-TURBINE-ID

  • WIND-TURBINE-ID: character(8): Wind turbine identifier. The value `NONE' is not allowed.

1.5. Wind references for wind velocity, one input line

WIND_REF AERO_DLL

  • WIND_REF: character: Coupled analysis: Reference to floater force model (SIMO body) for wind velocity. Must be given for coupled analysis, dummy if not coupled analysis.

  • AERO_DLL: character, default: 'NONE': Code for AERODYN DLL (Educational feature)

    • AERO_DLL = NONE : Official RIFLEX version

    • AERO_DLL = EXTE : Restricted option only available for selected academic users

For coupled analyses with SIMO wind type IWITYP >= 10, the incoming wind is calculated at the updated nodal coordinates of the nodes along the blades.

For coupled analyses with SIMO wind type IWITYP < 10, the wind at the SIMO body WIND_REF is reported. Note that this wind is calculated at the wind force coefficient height ZCOEFF. This wind is also used as the incoming wind along the blades .

1.6. Wind load options, one input line

CLMOM    CUPWN   IWTADV

  • CLMOM: character, default: 'ON': ON-OFF switch for inclusion of wind moment around longitudinal axis of the blades.

    • CLMOM = ON: Include wind moment

    • CLMOM = OFF: Exclude wind moment and disregard distance between foil center and pitch axis

  • CUPWN: character, default: 'UPWN': switch for upwind or downwind turbine

    • CUPWN = UPWN: Upwind turbine

    • CUPWN = DNWN: Downwind turbine

  • IWTADV: integer, default: 0: switch for advanced wind turbine aerodynamic options

    • IWTADV = 0: Default wind turbine aerodynamic options

    • IWTADV = N: Number of lines with advanced wind turbine aerodynamic options

1.7. Advanced wind turbine aerodynamic load options, IWTADV>0, IWTADV input lines

CHID    CHSW

  • CHID: character(4) : identifier for switch to be given

  • CHSW: character(3) : on-off switch

  • `CHVA: real : input value

Legal combinations of CHID, CHSW and CHVA include:

  • CHID == INDU: induction calculation

    • CHSW = OFF: No induction calculation (parked turbine)

    • CHSW = ON: Induction calculation included (default)

  • CHID == PRTI: Prandtl tip correction

    • CHSW = OFF: No Prandtl correction applied at the blade tip

    • CHSW = ON: Prandtl correction applied at the blade tip (default)

  • CHID == PRRO: Prandtl root correction

    • CHSW = OFF: No Prandtl correction applied at the blade root (default)

    • CHSW = ON: Prandtl correction applied at the blade root

  • CHID == PRYA: Prandtl factor correction for yaw

    • CHSW = OFF: Keep angle \(\mathrm {\phi }\) constant regardless of yawed inflow

    • CHSW = ON: Correct angle \(\mathrm {\phi }\) in the Prandtl factor for yawed inflow (default)

  • CHID == KYAW: Prandtl root correction

    • CHSW = OFF:

    • CHSW = ON:

      • CHVA = 1.0 : Default skew wake factor

      • CHVA = N : Value used for the user defined skew wake factor

CHVA is only used for CHID==KYAW and CHSW==ON. For all other cases this value is dummy.

1.8. Control systems for blade pitch, electrical power and nacelle yaw, one input line

Specification of blade pitch and electrical power control system, internal and external.

Specification of internal or external yaw control system (external not yet implemented) nacelle yaw controller.

Specification of external combined blade pitch, electrical power and yaw control system external.

CHCODE  YAWCCODE LOGCODE

  • CHCODE: character(4):

    • CHCODE = INTC: Internal blade pitch and electrical power control system

    • CHCODE = EXTC: External blade pitch and electrical power control system

  • YAWCCODE: character(4), default: NONE: Control system used for yaw

    • YAWCCODE = NONE: No yaw control system

    • YAWCCODE = YCIN: Internal yaw control system

    • YAWCCODE = YCEX: External yaw control system (not implemented)

    • YAWCCODE = COMB: External combined blade pitch, electrical power and yaw control system. Legal for CHCODE = EXTC only.

  • LOGCODE: character(3), default: `OFF:

    • LOGCODE = OFF: Logging of signals to/from controller is not activated (recommended)

    • LOGCODE = ON : Logging of signals to/from controller is activated. This option should only be used for debugging purposes.

LOGCODE is implemented for external controller, CHCODE = EXTC, only.
Logging of the controller signals, LOGCODE = ON, will generate a ascii-file that may require large storage space.
Internal control system input for blade pitch and electrical power, CHCODE = INTC, one input line
FILE_NAME

Descriptions of the internal control system and file format are found in Specification of internal control system for blade pitch and electrical power.

External control system input for blade pitch and electrical power, CHCODE = EXTC, 3 input lines
JarName
ClassName
Config

The external control system may be either a Java .jar file or a DLL with a Bladded interface. A description of the input and the interface for the external control system is given in Control system files needed for RIFLEX simulation.

Specification of nodes and elements for additional measurements, CHCODE = EXTC
NNOD_MEAS  NEL_MEAS

  • NNOD_MEAS: integer, default: 0: Number of nodes for which additional measurements will be sent to the external control system. NNOD_MEAS = 0 for the internal control system.

  • NEL_MEAS: integer, default: 0: Number of elements for which additional measurements will be sent to the external control system. NEL_MEAS = 0 for the internal control system.

Specification of nodes for additional measurements, NNOD_MEAS input lines
LINE-ID ISEG INOD SYSTEM

  • LINE-ID: character(8): Line identifier

  • ISEG: integer > 0: Local segment number in specified line

  • INOD: integer > 0: Local node number in specified segment

  • SYSTEM: character(6), default: 'GLOBAL': switch for reference system for the nodal measurements exported to the external controller.

    • SYSTEM = GLOBAL: Displacement, velocity and acceleration in the global coordinate system

    • SYSTEM = SHAFT0: Displacement, velocity and acceleration in the initial shaft system

Specification of elements for additional measurements, NEL_MEAS input lines
LINE-ID ISEG IEL SYSTEM

  • LINE-ID: character(8): Line identifier

  • ISEG: integer > 0: Local segment number in specified line

  • IEL: integer > 0: Local node number in specified segment

  • SYSTEM: character(6), default: 'LOCAL': switch for reference system for the element measurements exported to the external controller.

    • SYSTEM = LOCAL: Element forces and moments in the local element

    • SYSTEM = SHAFT0: Element forces and moments in the initial shaft system

1.9. Shaft and tower specification, one input line

LINE-IDSFT LINE-IDTWR  BAK  ICDCOR

  • LINE-IDSFT: character(8): Reference to the line that is used for shaft modelling.

  • LINE-IDTWR: character(8), default: 'NONE': Reference to the line that is used for tower modelling.

    • If specified the incoming wind acting on the blades will be modified due to the presence of the tower.

  • BAK: real, default: 0.1: Bak modification factor for tower shadow, only used when tower drag is included (ICDCOR=1). If ICDCOR=0, the Bak factor is always 0. For down-wind turbines, the Bak factor is dummy.

  • ICDCOR: integer, default: 0: Option for modification of the tower shadow based on the tower drag. This value is dummy for down-wind turbines.

One and only one flex-joint has to be specified within the shaft line (line type). The flex-joint has to be fixed in the bending degrees of freedom and be given a specified stiffness in the torsional degree of freedom. The specified torsion stiffness will be used during static analysis. During dynamic analysis, the torsion will be controlled be the regulator.

1.10. Number of blades in the rotor, one input line

NBLADE

  • NBLADE: integer: Number of blades

1.11. Blade identification, NBLADE input lines

LINE1-ID LINE2-ID

  • LINE1-ID: character(8): Reference to the inner line of the blade (eccentricity).

  • LINE2-ID: character(8): Reference to the outer line of the blade (foils).

The supernode at the eccentricity has to be master node and the supernode at the blade the slave node in the the rigid supernode connection between the eccentricity and the blade.

1.12. Specification of internal or external control system for nacelle yaw, one input line

Internal yaw control system input, YAWCCODE=YCIN, 1 input lines
FILE_NAME

Descriptions of the internal yaw control system and file format are found in Specification of internal control system for nacelle yaw.

Yaw element identification, YAWCCODE=YCEX, YAWCCODE=YCIN or YAWCCODE=COMB, 1 input line
REFLINE-ID YAWLINE-ID

  • REFLINE-ID: character(8): Reference to the line that connected to the yaw element.

  • YAWLINE-ID: character(8): Reference to the yaw element.