The effect of Tilt Angle

Wind & Water Rotor Aerodynamics
1

Hi,

I am wondering the effect of tilt angle error for aerodynamic performance of wind turbine by FAST code. As I know, the effect of tilt angle is the same with yaw angle. It means that the aerodynamic power and thrust tend to decrease due to the effect of yaw/tilt error. When I used FAST code to simulate onshore 5MW wind turbine, I realized that the aerodynamic thrust with titlt angle condition is higher than case without titl angle condition. Can anyone give me advise?

Belows are some input for FAST simulation:

  1. All structure DOFs was diabled.
  2. Pitch, Yaw, ang Generator mode were also diabled.
  3. All freestream velocity and rotating speed were applied from Dr.Jonkman’s report (J. Jonkman, et al., “Definition of a 5MW Reference Wind Turbine for Offshore System Development”, Technical Report NREL/TP-500-38060, 2009.)
  4. Dynamic Stall option was enabled.

Because I can not attach figure, I post those aerodynamic thrust and power magnitude, here.

  1. Aerodynamic Thrust (kN)—> Unlike my expectation
    Pitch(deg) rpm Velocity FAST_BEM FAST_GDW FAST_BEM FAST_GDW
    (No Tilt) (No Tilt) (Tilt) (Tilt)
    0.0000 9.1600 8.0000 473.8000 484.9000 381.5000 391.9000
    0.0000 11.8900 11.0000 786.2000 803.9000 695.7000 712.0000
    10.4500 12.1000 15.0000 514.0000 508.1000 424.5000 418.2000
    17.4700 12.1000 20.0000 413.7000 402.9000 326.1000 315.0000
    23.4700 12.1000 25.0000 364.6000 343.6000 278.4000 259.4000

  2. Aerodynamic Power (kW) —> Like my expectation
    Pitch(deg) rpm Velocity FAST_BEM FAST_GDW FAST_BEM FAST_GDW
    (No Tilt) (No Tilt) (Tilt) (Tilt)
    0.0000 9.1600 8.0000 1879.0000 1980.0000 1898.0000 1990.0000
    0.0000 11.8900 11.0000 4855.0000 5079.0000 4907.0000 5109.0000
    10.4500 12.1000 15.0000 5286.0000 5182.0000 5362.0000 5251.0000
    17.4700 12.1000 20.0000 5276.0000 5041.0000 5406.0000 5165.0000
    23.4700 12.1000 25.0000 5259.0000 4725.0000 5432.0000 4947.0000

Cheers,

ToanThanh, Tran

2

Dear ToanThan Tran,

I’m assuming that your column labels are switched. My guess is that the columns 4-5 are with tilt and columns 6-7 are without tilt. With this labeling, your tables show that tilt increases thrust and reduces power, whereas you’d expect both to reduce with tilt.

Power is reducing with tilt as you’d expect, but thrust is not. I’m not sure how you derived what you label as “aerodynamic thrust”, but my guess is that you are using FAST output RotThrust (or equivalently, LSShftFxa). However, FAST output RotThrust not only includes the applied aerodynamic thrust, but also the gravity and inertial loads of the rotor. You’ve disabled all structural DOFs, so, the inertial loads are zero. However, the gravity load is still nonzero. For a rigid structure, the gravity load contribution to RotThrust is -RotMassGravitySIN(ShftTilt). To increase tower clearance, ShftTilt is negative in FAST for an upwind turbine, so, the gravity load adds to the aerodynamic thrust for an upwind turbine. To increase tower clearance, ShftTilt is positive in FAST for a downwind turbine, so, the gravity load subtracts from aerodynamic thrust for a downwind turbine.

I hope that helps.

Best regards,

3

Dear Jason,

Thank you for your response.
Absolutely, your guess is right. I made mistake when I posted tables.
You are right because I am using FAST output RotThrust. Therefor, it includes gravity and inertial loads of the rotor as you mentioned above. I understood that my thrust values include gravity load contribution (-RotMassGravitySIN(ShftTilt)) for tilt angle case. That’ why thrust value with tilt angle case is larger than case without tilt angle.
Thank you so much.

Best regards,

ToanThanh, Tran

4

Dear Jason,

I plan to compare the aerodynamic thrust and power of floating offshore wind turbine. As you mentioned before, the RotThrust output of FAST code is included the gravitational effect of rotor mass due to the tilt angle (5 degree). I am wondering that how we can extract a pure aerodynamic thrust in case of floating offshore wind turbine simulation. As we know, the gravitational effect of rotor mass must be changed due to the rotational modes of platform motion. Therefore, I think that the RotThrust output of FAST code should be subtracted the gravitational effect of rotor mass considering the rotational motion of platform (e.g., pitch, roll, and yaw). Moreover, the structural force due to a platform acceleration should be included. Could you give me your comment on this problem.

I really appreciate your help.
I looking forward to hearing from you soon.

5

Dear ToanTranh,

I agree with your comments. The tilt angle used when subtracting the rotor gravity term from the rotor thrust should include the effects of tilt due to deflection of the support structure.

To eliminate the rotor inertial contribution to the thrust, you could average the result over some time scale much larger than the natural periods of structural oscillation.

We are expecting to release an update to FAST v8 soon that includes the long-awaited AeroDyn overhaul (AeroDyn v15) (among other changes). You’ll be happy to know that we’ve added a pure aerodynamic rotor thrust output (plus many other outputs) to this version of AeroDyn.

Best regards,

6

Dear Jason,

Thank you for your quickly response.
I am happy to hear that the next release of FAST code will be added more output functions and others. I am looking forward to downloading it.

Again, thank you for your comments.

7

Dear jason,
I am writing a program to calculate the motion response of the OC3 FOWT system under wind and waves, and I only consider the motion in the direction of surge,heave and pitch. In the calculation process, I regard the OC3 system as a rigid body. Firstly, I calculate the motion response of OC3 system under regular wave(no wind), the calculated results are compared with those calculated by Openfast, and they are basically consistent, the response of the heave motion is as follows:

regularwave-heave
regularwave-heave1920×1470 95.2 KB

Later, I calculated the motion response of OC3 system under regular wave and uniform wind speed(use BEM method), the angle of pitch motion is represented by sita, therefore, the aerodynamic force of the FOWT system in the x direction and the z direction can be expressed as: Fx = Thrustcos(sita), Fz = -Thrustsin(sita), the aerodynamic moment My can be expressed as: My = Thrust*Hub height. “Thrust” is the aerodynamic thrust calculated by the BEM method, I compared the calculation results of Fx and Fz with those of “RtAeroFxg” and “RtAeroFzg” in Openfast, and they were roughly the same. In addition, I compared the motion response of surge, heave and pitch of the FOWT, and the calculation results of surge and pitch were also consistent with the results of Openfast, but there was a big difference between the results of heave:
regularwave-wind-surge
regularwave-wind-surge1920×1470 48.1 KB

regularwave-wind-heave
regularwave-wind-heave1920×1470 63.1 KB

regularwave-wind-pitch
regularwave-wind-pitch1920×1470 55.7 KB

regularwave-wind-aeroFx
regularwave-wind-aeroFx1920×1470 85.9 KB

regularwave-wind-aeroFz
regularwave-wind-aeroFz1920×1470 70.5 KB

Through analysis, I think I neglected some terms in the calculation of vertical aerodynamic force Fz, however, the result of Fz is almost the same as “RtAeroFzg”, which makes me not know what is missing, can you give me some suggestions?

Best regards
Lin.Yang

8

Dear @Lin.Yang2,

It looks like your heave motion differs from OpenFAST when the surge motion is large, which suggests to me that something in your model is different from OpenFAST related to surge-have coupling. Perhaps this is tied to differences in how the moorings are modeled between OpenFAST and your model?

Best regards

9

Dear jason,
Thank you for your response! You’re right, I only used the linearized mooring stiffness matrix in my calculation program. Today I call “Moordyn” in my program to calculate the mooring force, however, the results are not much different from the results calculated using linear stiffness matrix. I guess when I turn on Aerodyn, the vertical force Fz calculated by Aerodyn doesn’t just include RtAeroFzg? The following are Aerodyn, ElastoDyn and .fst documents, tower aerodynamic loads are not taken into account in either calculation. Thank you again for your kind help！

Best regards
Lin.Yang

------- AERODYN v15 for OpenFAST INPUT FILE -----------------------------------------------
NREL 5.0 MW offshore baseline aerodynamic input properties.
======  General Options  ============================================================================
False         Echo               - Echo the input to "<rootname>.AD.ech"?  (flag)
"default"     DTAero             - Time interval for aerodynamic calculations {or "default"} (s)
          1   WakeMod            - Type of wake/induction model (switch) {0=none, 1=BEMT, 2=DBEMT, 3=OLAF} [WakeMod cannot be 2 or 3 when linearizing]
          1   AFAeroMod          - Type of blade airfoil aerodynamics model (switch) {1=steady model, 2=Beddoes-Leishman unsteady model} [AFAeroMod must be 1 when linearizing]
          0   TwrPotent          - Type tower influence on wind based on potential flow around the tower (switch) {0=none, 1=baseline potential flow, 2=potential flow with Bak correction}
          0   TwrShadow          - Calculate tower influence on wind based on downstream tower shadow (switch) {0=none, 1=Powles model, 2=Eames model}
False          TwrAero           - Calculate tower aerodynamic loads? (flag)
False         FrozenWake         - Assume frozen wake during linearization? (flag) [used only when WakeMod=1 and when linearizing]
False         CavitCheck         - Perform cavitation check? (flag) [AFAeroMod must be 1 when CavitCheck=true]
False         Buoyancy           - Include buoyancy effects? (flag)
False         CompAA             - Flag to compute AeroAcoustics calculation [used only when WakeMod = 1 or 2]
"unused"      AA_InputFile       - AeroAcoustics input file [used only when CompAA=true]
======  Environmental Conditions  ===================================================================
"default"     AirDens            - Air density (kg/m^3)
"default"     KinVisc            - Kinematic viscosity of working fluid (m^2/s)
"default"     SpdSound           - Speed of sound in working fluid (m/s)
"default"     Patm               - Atmospheric pressure (Pa) [used only when CavitCheck=True]
"default"     Pvap               - Vapour pressure of working fluid (Pa) [used only when CavitCheck=True]
======  Blade-Element/Momentum Theory Options  ====================================================== [unused when WakeMod=0 or 3]
          2   SkewMod            - Type of skewed-wake correction model (switch) {1=uncoupled, 2=Pitt/Peters, 3=coupled} [unused when WakeMod=0 or 3]
"default"     SkewModFactor      - Constant used in Pitt/Peters skewed wake model {or "default" is 15/32*pi} (-) [used only when SkewMod=2; unused when WakeMod=0 or 3]
True          TipLoss            - Use the Prandtl tip-loss model? (flag) [unused when WakeMod=0 or 3]
True          HubLoss            - Use the Prandtl hub-loss model? (flag) [unused when WakeMod=0 or 3]
False          TanInd             - Include tangential induction in BEMT calculations? (flag) [unused when WakeMod=0 or 3]
False         AIDrag             - Include the drag term in the axial-induction calculation? (flag) [unused when WakeMod=0 or 3]
False         TIDrag             - Include the drag term in the tangential-induction calculation? (flag) [unused when WakeMod=0,3 or TanInd=FALSE]
"Default"     IndToler           - Convergence tolerance for BEMT nonlinear solve residual equation {or "default"} (-) [unused when WakeMod=0 or 3]
        100   MaxIter            - Maximum number of iteration steps (-) [unused when WakeMod=0]
======  Dynamic Blade-Element/Momentum Theory Options  ============================================== [used only when WakeMod=2]
          2   DBEMT_Mod          - Type of dynamic BEMT (DBEMT) model {1=constant tau1, 2=time-dependent tau1, 3=constant tau1 with continuous formulation} (-) [used only when WakeMod=2]
          4   tau1_const         - Time constant for DBEMT (s) [used only when WakeMod=2 and DBEMT_Mod=1 or 3] 
======  OLAF -- cOnvecting LAgrangian Filaments (Free Vortex Wake) Theory Options  ================== [used only when WakeMod=3]
"unused"      OLAFInputFileName  - Input file for OLAF [used only when WakeMod=3]
======  Beddoes-Leishman Unsteady Airfoil Aerodynamics Options  ===================================== [used only when AFAeroMod=2]
          3   UAMod              - Unsteady Aero Model Switch (switch) {2=B-L Gonzalez, 3=B-L Minnema/Pierce, 4=B-L HGM 4-states, 5=B-L 5 states, 6=Oye, 7=Boeing-Vertol} [used only when AFAeroMod=2]
True          FLookup            - Flag to indicate whether a lookup for f' will be calculated (TRUE) or whether best-fit exponential equations will be used (FALSE); if FALSE S1-S4 must be provided in airfoil input files (flag) [used only when AFAeroMod=2]
======  Airfoil Information =========================================================================
          1   AFTabMod           - Interpolation method for multiple airfoil tables {1=1D interpolation on AoA (first table only); 2=2D interpolation on AoA and Re; 3=2D interpolation on AoA and UserProp} (-)
          1   InCol_Alfa         - The column in the airfoil tables that contains the angle of attack (-)
          2   InCol_Cl           - The column in the airfoil tables that contains the lift coefficient (-)
          3   InCol_Cd           - The column in the airfoil tables that contains the drag coefficient (-)
          4   InCol_Cm           - The column in the airfoil tables that contains the pitching-moment coefficient; use zero if there is no Cm column (-)
          0   InCol_Cpmin        - The column in the airfoil tables that contains the Cpmin coefficient; use zero if there is no Cpmin column (-)
          8   NumAFfiles         - Number of airfoil files used (-)
"../5MW_Baseline/Airfoils/Cylinder1.dat"    AFNames            - Airfoil file names (NumAFfiles lines) (quoted strings)
"../5MW_Baseline/Airfoils/Cylinder2.dat"
"../5MW_Baseline/Airfoils/DU40_A17.dat"
"../5MW_Baseline/Airfoils/DU35_A17.dat"
"../5MW_Baseline/Airfoils/DU30_A17.dat"
"../5MW_Baseline/Airfoils/DU25_A17.dat"
"../5MW_Baseline/Airfoils/DU21_A17.dat"
"../5MW_Baseline/Airfoils/NACA64_A17.dat"
======  Rotor/Blade Properties  =====================================================================
False          UseBlCm            - Include aerodynamic pitching moment in calculations?  (flag)
"../5MW_Baseline/NRELOffshrBsline5MW_AeroDyn_blade.dat"    ADBlFile(1)        - Name of file containing distributed aerodynamic properties for Blade #1 (-)
"../5MW_Baseline/NRELOffshrBsline5MW_AeroDyn_blade.dat"    ADBlFile(2)        - Name of file containing distributed aerodynamic properties for Blade #2 (-) [unused if NumBl < 2]
"../5MW_Baseline/NRELOffshrBsline5MW_AeroDyn_blade.dat"    ADBlFile(3)        - Name of file containing distributed aerodynamic properties for Blade #3 (-) [unused if NumBl < 3]
======  Hub Properties ============================================================================== [used only when Buoyancy=True]
0.0   VolHub             - Hub volume (m^3)
0.0   HubCenBx           - Hub center of buoyancy x direction offset (m)
======  Nacelle Properties ========================================================================== [used only when Buoyancy=True]
0.0   VolNac             - Nacelle volume (m^3)
0,0,0 NacCenB            - Position of nacelle center of buoyancy from yaw bearing in nacelle coordinates (m)
======  Tail fin Aerodynamics ======================================================================== 
False         TFinAero           - Calculate tail fin aerodynamics model (flag)
"unused"      TFinFile           - Input file for tail fin aerodynamics [used only when TFinAero=True]
======  Tower Influence and Aerodynamics ============================================================ [used only when TwrPotent/=0, TwrShadow/=0, TwrAero=True, or Buoyancy=True]
         11   NumTwrNds         - Number of tower nodes used in the analysis  (-) [used only when TwrPotent/=0, TwrShadow/=0, TwrAero=True, or Buoyancy=True]
TwrElev        TwrDiam        TwrCd          TwrTI          TwrCb !TwrTI used only with TwrShadow=2, TwrCb used only with Buoyancy=True
(m)              (m)           (-)            (-)           (-)
1.0000000E+01  6.5000000E+00  1.0000000E+00  1.0000000E-01  0.0
1.7760000E+01  6.2400000E+00  1.0000000E+00  1.0000000E-01  0.0
2.5520000E+01  5.9700000E+00  1.0000000E+00  1.0000000E-01  0.0
3.3280000E+01  5.7100000E+00  1.0000000E+00  1.0000000E-01  0.0
4.1040000E+01  5.4500000E+00  1.0000000E+00  1.0000000E-01  0.0
4.8800000E+01  5.1800000E+00  1.0000000E+00  1.0000000E-01  0.0
5.6560000E+01  4.9200000E+00  1.0000000E+00  1.0000000E-01  0.0
6.4320000E+01  4.6600000E+00  1.0000000E+00  1.0000000E-01  0.0
7.2080000E+01  4.4000000E+00  1.0000000E+00  1.0000000E-01  0.0
7.9840000E+01  4.1300000E+00  1.0000000E+00  1.0000000E-01  0.0
8.7600000E+01  3.8700000E+00  1.0000000E+00  1.0000000E-01  0.0
======  Outputs  ====================================================================================
True          SumPrint            - Generate a summary file listing input options and interpolated properties to "<rootname>.AD.sum"?  (flag)
          3   NBlOuts             - Number of blade node outputs [0 - 9] (-)
          1,          9,         19    BlOutNd             - Blade nodes whose values will be output  (-)
          0   NTwOuts             - Number of tower node outputs [0 - 9]  (-)
          1,          2,          6    TwOutNd             - Tower nodes whose values will be output  (-)
                   OutList             - The next line(s) contains a list of output parameters.  See OutListParameters.xlsx for a listing of available output channels, (-)
"RtAeroFxg"
"RtAeroFyg"
"RtAeroFzg"
"RtAeroMxg"
"RtAeroMyg"
"RtAeroMzg"
"RtAeroPwr"
"RtAeroFxh"
"RtAeroFyh"
"RtAeroFzh"
"RtAeroMxh"
"RtAeroMyh"
"RtAeroMzh"  
END of input file (the word "END" must appear in the first 3 columns of this last OutList line)
---------------------------------------------------------------------------------------

------- ELASTODYN for OpenFAST INPUT FILE -------------------------------------------
NREL 5.0 MW Baseline Wind Turbine for Use in Offshore Analysis. Properties from Dutch Offshore Wind Energy Converter (DOWEC) 6MW Pre-Design (10046_009.pdf) and REpower 5M 5MW (5m_uk.pdf)
---------------------- SIMULATION CONTROL --------------------------------------
False         Echo        - Echo input data to "<RootName>.ech" (flag)
          3   Method      - Integration method: {1: RK4, 2: AB4, or 3: ABM4} (-)
"default"     DT          - Integration time step (s)
---------------------- DEGREES OF FREEDOM --------------------------------------
False          FlapDOF1    - First flapwise blade mode DOF (flag)
False          FlapDOF2    - Second flapwise blade mode DOF (flag)
False          EdgeDOF     - First edgewise blade mode DOF (flag)
False          TeetDOF     - Rotor-teeter DOF (flag) [unused for 3 blades]
False          DrTrDOF     - Drivetrain rotational-flexibility DOF (flag)
False          GenDOF      - Generator DOF (flag)
False          YawDOF      - Yaw DOF (flag)
False          TwFADOF1    - First fore-aft tower bending-mode DOF (flag)
False          TwFADOF2    - Second fore-aft tower bending-mode DOF (flag)
False          TwSSDOF1    - First side-to-side tower bending-mode DOF (flag)
False          TwSSDOF2    - Second side-to-side tower bending-mode DOF (flag)
True           PtfmSgDOF   - Platform horizontal surge translation DOF (flag)
False           PtfmSwDOF   - Platform horizontal sway translation DOF (flag)
True           PtfmHvDOF   - Platform vertical heave translation DOF (flag)
False           PtfmRDOF    - Platform roll tilt rotation DOF (flag)
True           PtfmPDOF    - Platform pitch tilt rotation DOF (flag)
False           PtfmYDOF    - Platform yaw rotation DOF (flag)
---------------------- INITIAL CONDITIONS --------------------------------------
          0   OoPDefl     - Initial out-of-plane blade-tip displacement (meters)
          0   IPDefl      - Initial in-plane blade-tip deflection (meters)
          0   BlPitch(1)  - Blade 1 initial pitch (degrees)
          0   BlPitch(2)  - Blade 2 initial pitch (degrees)
          0   BlPitch(3)  - Blade 3 initial pitch (degrees) [unused for 2 blades]
          0   TeetDefl    - Initial or fixed teeter angle (degrees) [unused for 3 blades]
          0   Azimuth     - Initial azimuth angle for blade 1 (degrees)
       12.1   RotSpeed    - Initial or fixed rotor speed (rpm)
          0   NacYaw      - Initial or fixed nacelle-yaw angle (degrees)
          0   TTDspFA     - Initial fore-aft tower-top displacement (meters)
          0   TTDspSS     - Initial side-to-side tower-top displacement (meters)
          0   PtfmSurge   - Initial or fixed horizontal surge translational displacement of platform (meters)
          0   PtfmSway    - Initial or fixed horizontal sway translational displacement of platform (meters)
          0   PtfmHeave   - Initial or fixed vertical heave translational displacement of platform (meters)
          0   PtfmRoll    - Initial or fixed roll tilt rotational displacement of platform (degrees)
          0   PtfmPitch   - Initial or fixed pitch tilt rotational displacement of platform (degrees)
          0   PtfmYaw     - Initial or fixed yaw rotational displacement of platform (degrees)
---------------------- TURBINE CONFIGURATION -----------------------------------
          3   NumBl       - Number of blades (-)
         63   TipRad      - The distance from the rotor apex to the blade tip (meters)
        1.5   HubRad      - The distance from the rotor apex to the blade root (meters)
         0   PreCone(1)  - Blade 1 cone angle (degrees)
         0   PreCone(2)  - Blade 2 cone angle (degrees)
         0   PreCone(3)  - Blade 3 cone angle (degrees) [unused for 2 blades]
          0   HubCM       - Distance from rotor apex to hub mass [positive downwind] (meters)
          0   UndSling    - Undersling length [distance from teeter pin to the rotor apex] (meters) [unused for 3 blades]
          0   Delta3      - Delta-3 angle for teetering rotors (degrees) [unused for 3 blades]
          0   AzimB1Up    - Azimuth value to use for I/O when blade 1 points up (degrees)
    -5.0191   OverHang    - Distance from yaw axis to rotor apex [3 blades] or teeter pin [2 blades] (meters)
      1.912   ShftGagL    - Distance from rotor apex [3 blades] or teeter pin [2 blades] to shaft strain gages [positive for upwind rotors] (meters)
         0   ShftTilt    - Rotor shaft tilt angle (degrees)
        1.9   NacCMxn     - Downwind distance from the tower-top to the nacelle CM (meters)
          0   NacCMyn     - Lateral  distance from the tower-top to the nacelle CM (meters)
       1.75   NacCMzn     - Vertical distance from the tower-top to the nacelle CM (meters)
   -3.09528   NcIMUxn     - Downwind distance from the tower-top to the nacelle IMU (meters)
          0   NcIMUyn     - Lateral  distance from the tower-top to the nacelle IMU (meters)
    2.23336   NcIMUzn     - Vertical distance from the tower-top to the nacelle IMU (meters)
    1.96256   Twr2Shft    - Vertical distance from the tower-top to the rotor shaft (meters)
       87.6   TowerHt     - Height of tower relative to ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] (meters)
         10   TowerBsHt   - Height of tower base relative to ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] (meters)
          0   PtfmCMxt    - Downwind distance from the ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] to the platform CM (meters)
          0   PtfmCMyt    - Lateral distance from the ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] to the platform CM (meters)
   -89.9155   PtfmCMzt    - Vertical distance from the ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] to the platform CM (meters)
         -0   PtfmRefzt   - Vertical distance from the ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] to the platform reference point (meters)
---------------------- MASS AND INERTIA ----------------------------------------
          0   TipMass(1)  - Tip-brake mass, blade 1 (kg)
          0   TipMass(2)  - Tip-brake mass, blade 2 (kg)
          0   TipMass(3)  - Tip-brake mass, blade 3 (kg) [unused for 2 blades]
      56780   HubMass     - Hub mass (kg)
     115926   HubIner     - Hub inertia about rotor axis [3 blades] or teeter axis [2 blades] (kg m^2)
    534.116   GenIner     - Generator inertia about HSS (kg m^2)
     240000   NacMass     - Nacelle mass (kg)
2.60789E+06   NacYIner    - Nacelle inertia about yaw axis (kg m^2)
          0   YawBrMass   - Yaw bearing mass (kg)
7.46633E+06   PtfmMass    - Platform mass (kg)
4.22923E+09   PtfmRIner   - Platform inertia for roll tilt rotation about the platform CM (kg m^2)
4.22923E+09   PtfmPIner   - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)
 1.6423E+08   PtfmYIner   - Platform inertia for yaw rotation about the platform CM (kg m^2)
---------------------- BLADE ---------------------------------------------------
         17   BldNodes    - Number of blade nodes (per blade) used for analysis (-)
"../5MW_Baseline/NRELOffshrBsline5MW_Blade.dat"    BldFile(1)  - Name of file containing properties for blade 1 (quoted string)
"../5MW_Baseline/NRELOffshrBsline5MW_Blade.dat"    BldFile(2)  - Name of file containing properties for blade 2 (quoted string)
"../5MW_Baseline/NRELOffshrBsline5MW_Blade.dat"    BldFile(3)  - Name of file containing properties for blade 3 (quoted string) [unused for 2 blades]
---------------------- ROTOR-TEETER --------------------------------------------
          0   TeetMod     - Rotor-teeter spring/damper model {0: none, 1: standard, 2: user-defined from routine UserTeet} (switch) [unused for 3 blades]
          0   TeetDmpP    - Rotor-teeter damper position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetDmp     - Rotor-teeter damping constant (N-m/(rad/s)) [used only for 2 blades and when TeetMod=1]
          0   TeetCDmp    - Rotor-teeter rate-independent Coulomb-damping moment (N-m) [used only for 2 blades and when TeetMod=1]
          0   TeetSStP    - Rotor-teeter soft-stop position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetHStP    - Rotor-teeter hard-stop position (degrees) [used only for 2 blades and when TeetMod=1]
          0   TeetSSSp    - Rotor-teeter soft-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
          0   TeetHSSp    - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
---------------------- DRIVETRAIN ----------------------------------------------
        100   GBoxEff     - Gearbox efficiency (%)
         97   GBRatio     - Gearbox ratio (-)
8.67637E+08   DTTorSpr    - Drivetrain torsional spring (N-m/rad)
  6.215E+06   DTTorDmp    - Drivetrain torsional damper (N-m/(rad/s))
---------------------- FURLING -------------------------------------------------
False         Furling     - Read in additional model properties for furling turbine (flag) [must currently be FALSE)
"unused"      FurlFile    - Name of file containing furling properties (quoted string) [unused when Furling=False]
---------------------- TOWER ---------------------------------------------------
         20   TwrNodes    - Number of tower nodes used for analysis (-)
"NRELOffshrBsline5MW_OC3Hywind_ElastoDyn_Tower.dat"    TwrFile     - Name of file containing tower properties (quoted string)
---------------------- OUTPUT --------------------------------------------------
True          SumPrint    - Print summary data to "<RootName>.sum" (flag)
          1   OutFile     - Switch to determine where output will be placed: {1: in module output file only; 2: in glue code output file only; 3: both} (currently unused)
True          TabDelim    - Use tab delimiters in text tabular output file? (flag) (currently unused)
"ES10.3E2"    OutFmt      - Format used for text tabular output (except time).  Resulting field should be 10 characters. (quoted string) (currently unused)
         30   TStart      - Time to begin tabular output (s) (currently unused)
          1   DecFact     - Decimation factor for tabular output {1: output every time step} (-) (currently unused)
          1   NTwGages    - Number of tower nodes that have strain gages for output [0 to 9] (-)
         10   TwrGagNd    - List of tower nodes that have strain gages [1 to TwrNodes] (-) [unused if NTwGages=0]
          1   NBlGages    - Number of blade nodes that have strain gages for output [0 to 9] (-)
          9   BldGagNd    - List of blade nodes that have strain gages [1 to BldNodes] (-) [unused if NBlGages=0]
              OutList     - The next line(s) contains a list of output parameters.  See OutListParameters.xlsx for a listing of available output channels, (-)
"BldPitch1"               - Pitch angles for blades 1, 2, and 3
"BldPitch2"               - Pitch angles for blades 1, 2, and 3
"BldPitch3"               - Pitch angles for blades 1, 2, and 3
"Azimuth"                 - Blade 1 azimuth angle
"PtfmSurge"
"PtfmSway"
"PtfmHeave"
"PtfmRoll"
"PtfmPitch"
"PtfmYaw"
"LSShftFxa"
"LSShftFya"
"LSShftFza"
"LSShftMxa"
"LSSTipMya"
"LSSTipMza"
END of input file (the word "END" must appear in the first 3 columns of this last OutList line)
---------------------------------------------------------------------------------------

------- OpenFAST EXAMPLE INPUT FILE -------------------------------------------
FAST Certification Test #24: NREL 5.0 MW Baseline Wind Turbine with OC3 Hywind Configuration, for use in offshore analysis
---------------------- SIMULATION CONTROL --------------------------------------
True          Echo            - Echo input data to <RootName>.ech (flag)
"FATAL"       AbortLevel      - Error level when simulation should abort (string) {"WARNING", "SEVERE", "FATAL"}
        200   TMax            - Total run time (s)
     0.0125   DT              - Recommended module time step (s)
          1   InterpOrder     - Interpolation order for input/output time history (-) {1=linear, 2=quadratic}
          0   NumCrctn        - Number of correction iterations (-) {0=explicit calculation, i.e., no corrections}
        1.5   DT_UJac         - Time between calls to get Jacobians (s)
      1E+06   UJacSclFact     - Scaling factor used in Jacobians (-)
---------------------- FEATURE SWITCHES AND FLAGS ------------------------------
          1   CompElast       - Compute structural dynamics (switch) {1=ElastoDyn; 2=ElastoDyn + BeamDyn for blades}
          1   CompInflow      - Compute inflow wind velocities (switch) {0=still air; 1=InflowWind; 2=external from OpenFOAM}
          2   CompAero        - Compute aerodynamic loads (switch) {0=None; 1=AeroDyn v14; 2=AeroDyn v15}
          0   CompServo       - Compute control and electrical-drive dynamics (switch) {0=None; 1=ServoDyn}
          1   CompHydro       - Compute hydrodynamic loads (switch) {0=None; 1=HydroDyn}
          0   CompSub         - Compute sub-structural dynamics (switch) {0=None; 1=SubDyn; 2=External Platform MCKF}
          3   CompMooring     - Compute mooring system (switch) {0=None; 1=MAP++; 2=FEAMooring; 3=MoorDyn; 4=OrcaFlex}
          0   CompIce         - Compute ice loads (switch) {0=None; 1=IceFloe; 2=IceDyn}
          0   MHK             - MHK turbine type (switch) {0=Not an MHK turbine; 1=Fixed MHK turbine; 2=Floating MHK turbine}
---------------------- ENVIRONMENTAL CONDITIONS --------------------------------
    9.80665   Gravity         - Gravitational acceleration (m/s^2)
      1.225   AirDens         - Air density (kg/m^3)
       1025   WtrDens         - Water density (kg/m^3)
  1.464E-05   KinVisc         - Kinematic viscosity of working fluid (m^2/s)
        335   SpdSound        - Speed of sound in working fluid (m/s)
     103500   Patm            - Atmospheric pressure (Pa) [used only for an MHK turbine cavitation check]
       1700   Pvap            - Vapour pressure of working fluid (Pa) [used only for an MHK turbine cavitation check]
        320   WtrDpth         - Water depth (m)
          0   MSL2SWL         - Offset between still-water level and mean sea level (m) [positive upward]
---------------------- INPUT FILES ---------------------------------------------
"NRELOffshrBsline5MW_OC3Hywind_ElastoDyn.dat"    EDFile          - Name of file containing ElastoDyn input parameters (quoted string)
"../5MW_Baseline/NRELOffshrBsline5MW_BeamDyn.dat"    BDBldFile(1)    - Name of file containing BeamDyn input parameters for blade 1 (quoted string)
"../5MW_Baseline/NRELOffshrBsline5MW_BeamDyn.dat"    BDBldFile(2)    - Name of file containing BeamDyn input parameters for blade 2 (quoted string)
"../5MW_Baseline/NRELOffshrBsline5MW_BeamDyn.dat"    BDBldFile(3)    - Name of file containing BeamDyn input parameters for blade 3 (quoted string)
"../5MW_Baseline/NRELOffshrBsline5MW_InflowWind_12mps.dat"    InflowFile      - Name of file containing inflow wind input parameters (quoted string)
"NRELOffshrBsline5MW_OC3Hywind_AeroDyn15.dat"    AeroFile        - Name of file containing aerodynamic input parameters (quoted string)
"NRELOffshrBsline5MW_OC3Hywind_ServoDyn.dat"    ServoFile       - Name of file containing control and electrical-drive input parameters (quoted string)
"NRELOffshrBsline5MW_OC3Hywind_HydroDyn.dat"    HydroFile       - Name of file containing hydrodynamic input parameters (quoted string)
"unused"      SubFile         - Name of file containing sub-structural input parameters (quoted string)
"NRELOffshrBsline5MW_OC3Hywind_MoorDyn.dat"    MooringFile     - Name of file containing mooring system input parameters (quoted string)
"unused"      IceFile         - Name of file containing ice input parameters (quoted string)
---------------------- OUTPUT --------------------------------------------------
True          SumPrint        - Print summary data to "<RootName>.sum" (flag)
          1   SttsTime        - Amount of time between screen status messages (s)
      99999   ChkptTime       - Amount of time between creating checkpoint files for potential restart (s)
     0.0125   DT_Out          - Time step for tabular output (s) (or "default")
          0   TStart          - Time to begin tabular output (s)
          0   OutFileFmt      - Format for tabular (time-marching) output file (switch) {0: uncompressed binary [<RootName>.outb], 1: text file [<RootName>.out], 2: binary file [<RootName>.outb], 3: both 1 and 2}
True          TabDelim        - Use tab delimiters in text tabular output file? (flag) {uses spaces if false}
"ES15.7E2"    OutFmt          - Format used for text tabular output, excluding the time channel.  Resulting field should be 10 characters. (quoted string)
---------------------- LINEARIZATION -------------------------------------------
False         Linearize       - Linearization analysis (flag)
False         CalcSteady      - Calculate a steady-state periodic operating point before linearization? [unused if Linearize=False] (flag)
          3   TrimCase        - Controller parameter to be trimmed {1:yaw; 2:torque; 3:pitch} [used only if CalcSteady=True] (-)
      0.001   TrimTol         - Tolerance for the rotational speed convergence [used only if CalcSteady=True] (-)
       0.01   TrimGain        - Proportional gain for the rotational speed error (>0) [used only if CalcSteady=True] (rad/(rad/s) for yaw or pitch; Nm/(rad/s) for torque)
          0   Twr_Kdmp        - Damping factor for the tower [used only if CalcSteady=True] (N/(m/s))
          0   Bld_Kdmp        - Damping factor for the blades [used only if CalcSteady=True] (N/(m/s))
          2   NLinTimes       - Number of times to linearize (-) [>=1] [unused if Linearize=False]
         30,         60    LinTimes        - List of times at which to linearize (s) [1 to NLinTimes] [used only when Linearize=True and CalcSteady=False]
          1   LinInputs       - Inputs included in linearization (switch) {0=none; 1=standard; 2=all module inputs (debug)} [unused if Linearize=False]
          1   LinOutputs      - Outputs included in linearization (switch) {0=none; 1=from OutList(s); 2=all module outputs (debug)} [unused if Linearize=False]
False         LinOutJac       - Include full Jacobians in linearization output (for debug) (flag) [unused if Linearize=False; used only if LinInputs=LinOutputs=2]
False         LinOutMod       - Write module-level linearization output files in addition to output for full system? (flag) [unused if Linearize=False]
---------------------- VISUALIZATION ------------------------------------------
          0   WrVTK           - VTK visualization data output: (switch) {0=none; 1=initialization data only; 2=animation; 3=mode shapes}
          2   VTK_type        - Type of VTK visualization data: (switch) {1=surfaces; 2=basic meshes (lines/points); 3=all meshes (debug)} [unused if WrVTK=0]
false         VTK_fields      - Write mesh fields to VTK data files? (flag) {true/false} [unused if WrVTK=0]
         15   VTK_fps         - Frame rate for VTK output (frames per second){will use closest integer multiple of DT} [used only if WrVTK=2 or WrVTK=3]
10

Dear @Lin.Yang2,

I’m not exactly sure what you mean, but RtAeroFzg is the total aerodynamic load applied to the rotor in the vertical direction. Of course, other aerodynamic loads could impact platform heave motion, e.g., thrust forces would impact surge and pitch, which can influence heave through coupling.

Best regards,

11

Dear jason,
Thank you for your response! I found some issues with Moordyn, and maybe that’s why my motion results are different from Openfast’s results. Specifically, when I use Matlab to call the moordyn.dll file and compare the calculation results with the “MooringSystemFD.txt” data in the report “Definition of the Floating System for Phase IV of OC3”, I find that the results of the two are not complete same, especially when the displacement is large, there is a great difference between the two. For example, when the calculated displacement X is (-36 -36 -12 -0.1745 -0.1745 -0.3491), velocity XD=0, the results (F1-F6) in the report are (1555000 3716000 -2962000 2.915E8 -6.901E7 6.78E7), however, the results of my calculations are as follows:

Snipaste_2023-08-21_19-27-09
Snipaste_2023-08-21_19-27-091346×470 27.9 KB

(F1 = CON4FX + CON5FX + CON6FX = 7.4869e+05N)
(F3 = CON4FZ + CON5FZ + CON6FZ= -2816646N)
When the calculated displacement X is small (6, 6, -8, -0.03491, 0.1396, -0.2094), velocity XD=0, the results (F1-F6) in the report are (133000, -168700, -1531000, -8938000, -2.472E7, 4017000), the results of my calculations are:
Snipaste_2
Snipaste_21239×502 32.5 KB

(F1 = 136607N, F3 = -1528303N), that’s not far from the data in the report. The moordyn file I am using comes from the URL: Release Release v1.01.02 · FloatingArrayDesign/MoorDyn · GitHub, I believe it is correct. Can you give me some some suggestions? In addition, I have another question, Moordyn can not directly output the moment exerted by the mooring line on the platform, so the moment F4-F6 in the report is calculated by F1-F3? For example, F5 = F1*H, H is the vertical distance from the vessel to the reference point. I used the data in “MooringSystemFD.txt” to verify this, but the result was not so.

Best regards
Lin.Yang

12

Dear @Lin.Yang2,

Just a couple comments:

  • I’m not sure why MoorDyn is not matching the force-displacement values reported for the OC3-Hywind model at large displacement, but I do know that MoorDyn was not used in this calculation. Instead, the force-displacement relationships for the OC3-Hywind model were derived from the mooring module of FAST v7, which was a precursor to MAP++.
  • I agree that you can calculate the moments from fairlead forces, but in this calculation, you must take into account both the location of the fairlead relative to the reference point and the orientation (roll, pitch, yaw) of the floater.

Best regards,