I am currently looking at the force distribution along the blade of the NREL 5MW turbine. The model is set to work at rated and steady conditions of 11.4m/s and 12.1rpm, and ran both ElastoDyn and BeamDyn with AeroDyn15. I plotted FN and FT using, respectively:
Making sure that N9 is in fact the last node of the mesh.
As found in literature (but please correct me if I’m wrong anywhere in this post) I would have expected the forces to peak at around 0.8-0.9R, and drop close to zero in proximity of the blade tip. Instead, as shown below:
NO tip loss: the forces in FAST decrease only just slightly (but not as much as I thought they would)
INCLUDING tip loss: FT increases instead of dropping, and peaks at the tip
Similar plots are obtained with forces on the rotor plane, Fx and Fy. Could you explain this behaviour?
Are you using FAST v8.16 or OpenFAST v1.0.0 or something else? As explained in the OpenFAST v1.0.0 ReadMe file (wind.nrel.gov/nwtc/docs/README_OpenFAST.pdf), AeroDyn v15 was improved a lot between FAST v8.16 and OpenFAST v1.0.0.
I am using FAST v7 to calculate the forces and bending moments at each node of blade. The NREL 5MW bottom-fixed OWT was set to parked condition with wind speed of Vw=42.0m/s. The shear forces and bending moments at each node of each blade were extracted. However, some questions bothered me a lot.
(1) As displayed in following figures, the distribution of shear force and bending moment of blade 2 is quite different from that of blade 3. But I think they should be roughly the same for offshore wind turbine in paked state. Why is that?
(2) Is the difference between blade shear force and bending moment calculated by FAST v7 and OpenFAST large? And where can I download the latest version of OpenFAST?
The main input file is attached for your further check. Thanks in advance.
--------------------------------------------------------------------------------
------- FAST 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); Compatible with FAST v7.0.
---------------------- SIMULATION CONTROL --------------------------------------
True Echo - Echo input data to "echo.out" (flag)
1 ADAMSPrep - ADAMS preprocessor mode {1: Run FAST, 2: use FAST as a preprocessor to create an ADAMS model, 3: do both} (switch)
1 AnalMode - Analysis mode {1: Run a time-marching simulation, 2: create a periodic linearized model} (switch)
3 NumBl - Number of blades (-)
630.0 TMax - Total run time (s)
0.01 DT - Integration time step (s)
---------------------- TURBINE CONTROL -----------------------------------------
0 YCMode - Yaw control mode {0: none, 1: user-defined from routine UserYawCont, 2: user-defined from Simulink} (switch)
9999.9 TYCOn - Time to enable active yaw control (s) [unused when YCMode=0]
0 PCMode - Pitch control mode {0: none, 1: user-defined from routine PitchCntrl, 2: user-defined from Simulink} (switch)
9999.9 TPCOn - Time to enable active pitch control (s) [unused when PCMode=0]
2 VSContrl - Variable-speed control mode {0: none, 1: simple VS, 2: user-defined from routine UserVSCont, 3: user-defined from Simulink} (switch)
9999.9 VS_RtGnSp - Rated generator speed for simple variable-speed generator control (HSS side) (rpm) [used only when VSContrl=1]
9999.9 VS_RtTq - Rated generator torque/constant generator torque in Region 3 for simple variable-speed generator control (HSS side) (N-m) [used only when VSContrl=1]
9999.9 VS_Rgn2K - Generator torque constant in Region 2 for simple variable-speed generator control (HSS side) (N-m/rpm^2) [used only when VSContrl=1]
9999.9 VS_SlPc - Rated generator slip percentage in Region 2 1/2 for simple variable-speed generator control (%) [used only when VSContrl=1]
2 GenModel - Generator model {1: simple, 2: Thevenin, 3: user-defined from routine UserGen} (switch) [used only when VSContrl=0]
True GenTiStr - Method to start the generator {T: timed using TimGenOn, F: generator speed using SpdGenOn} (flag)
True GenTiStp - Method to stop the generator {T: timed using TimGenOf, F: when generator power = 0} (flag)
9999.9 SpdGenOn - Generator speed to turn on the generator for a startup (HSS speed) (rpm) [used only when GenTiStr=False]
9999.9 TimGenOn - Time to turn on the generator for a startup (s) [used only when GenTiStr=True]
9999.9 TimGenOf - Time to turn off the generator (s) [used only when GenTiStp=True]
2 HSSBrMode - HSS brake model {1: simple, 2: user-defined from routine UserHSSBr} (switch)
0 THSSBrDp - Time to initiate deployment of the HSS brake (s)
9999.9 TiDynBrk - Time to initiate deployment of the dynamic generator brake [CURRENTLY IGNORED] (s)
9999.9 TTpBrDp(1) - Time to initiate deployment of tip brake 1 (s)
9999.9 TTpBrDp(2) - Time to initiate deployment of tip brake 2 (s)
9999.9 TTpBrDp(3) - Time to initiate deployment of tip brake 3 (s) [unused for 2 blades]
9999.9 TBDepISp(1) - Deployment-initiation speed for the tip brake on blade 1 (rpm)
9999.9 TBDepISp(2) - Deployment-initiation speed for the tip brake on blade 2 (rpm)
9999.9 TBDepISp(3) - Deployment-initiation speed for the tip brake on blade 3 (rpm) [unused for 2 blades]
9999.9 TYawManS - Time to start override yaw maneuver and end standard yaw control (s)
9999.9 TYawManE - Time at which override yaw maneuver reaches final yaw angle (s)
0.0 NacYawF - Final yaw angle for override yaw maneuvers (degrees)
0.0 TPitManS(1) - Time to start override pitch maneuver for blade 1 and end standard pitch control (s)
0.0 TPitManS(2) - Time to start override pitch maneuver for blade 2 and end standard pitch control (s)
0.0 TPitManS(3) - Time to start override pitch maneuver for blade 3 and end standard pitch control (s) [unused for 2 blades]
0.0 TPitManE(1) - Time at which override pitch maneuver for blade 1 reaches final pitch (s)
0.0 TPitManE(2) - Time at which override pitch maneuver for blade 2 reaches final pitch (s)
0.0 TPitManE(3) - Time at which override pitch maneuver for blade 3 reaches final pitch (s) [unused for 2 blades]
90.0 BlPitch(1) - Blade 1 initial pitch (degrees)
90.0 BlPitch(2) - Blade 2 initial pitch (degrees)
90.0 BlPitch(3) - Blade 3 initial pitch (degrees) [unused for 2 blades]
90.0 BlPitchF(1) - Blade 1 final pitch for pitch maneuvers (degrees)
90.0 BlPitchF(2) - Blade 2 final pitch for pitch maneuvers (degrees)
90.0 BlPitchF(3) - Blade 3 final pitch for pitch maneuvers (degrees) [unused for 2 blades]
---------------------- ENVIRONMENTAL CONDITIONS --------------------------------
9.80665 Gravity - Gravitational acceleration (m/s^2)
---------------------- FEATURE FLAGS -------------------------------------------
True FlapDOF1 - First flapwise blade mode DOF (flag)
True FlapDOF2 - Second flapwise blade mode DOF (flag)
True EdgeDOF - First edgewise blade mode DOF (flag)
False TeetDOF - Rotor-teeter DOF (flag) [unused for 3 blades]
True DrTrDOF - Drivetrain rotational-flexibility DOF (flag)
False GenDOF - Generator DOF (flag)
False YawDOF - Yaw DOF (flag)
True TwFADOF1 - First fore-aft tower bending-mode DOF (flag)
True TwFADOF2 - Second fore-aft tower bending-mode DOF (flag)
True TwSSDOF1 - First side-to-side tower bending-mode DOF (flag)
True TwSSDOF2 - Second side-to-side tower bending-mode DOF (flag)
True CompAero - Compute aerodynamic forces (flag)
False CompNoise - Compute aerodynamic noise (flag)
---------------------- INITIAL CONDITIONS --------------------------------------
0.0 OoPDefl - Initial out-of-plane blade-tip displacement (meters)
0.0 IPDefl - Initial in-plane blade-tip deflection (meters)
0.0 TeetDefl - Initial or fixed teeter angle (degrees) [unused for 3 blades]
0.0 Azimuth - Initial azimuth angle for blade 1 (degrees)
0.0 RotSpeed - Initial or fixed rotor speed (rpm)
0.0 NacYaw - Initial or fixed nacelle-yaw angle (degrees)
0.0 TTDspFA - Initial fore-aft tower-top displacement (meters)
0.0 TTDspSS - Initial side-to-side tower-top displacement (meters)
---------------------- TURBINE CONFIGURATION -----------------------------------
63.0 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)
1 PSpnElN - Number of the innermost blade element which is still part of the pitchable portion of the blade for partial-span pitch control [1 to BldNodes] [CURRENTLY IGNORED] (-)
0.0 UndSling - Undersling length [distance from teeter pin to the rotor apex] (meters) [unused for 3 blades]
0.0 HubCM - Distance from rotor apex to hub mass [positive downwind] (meters)
-5.01910 OverHang - Distance from yaw axis to rotor apex [3 blades] or teeter pin [2 blades] (meters)
1.9 NacCMxn - Downwind distance from the tower-top to the nacelle CM (meters)
0.0 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)
87.6 TowerHt - Height of tower above ground level [onshore] or MSL [offshore] (meters)
1.96256 Twr2Shft - Vertical distance from the tower-top to the rotor shaft (meters)
0.0 TwrRBHt - Tower rigid base height (meters)
-5.0 ShftTilt - Rotor shaft tilt angle (degrees)
0.0 Delta3 - Delta-3 angle for teetering rotors (degrees) [unused for 3 blades]
-2.5 PreCone(1) - Blade 1 cone angle (degrees)
-2.5 PreCone(2) - Blade 2 cone angle (degrees)
-2.5 PreCone(3) - Blade 3 cone angle (degrees) [unused for 2 blades]
0.0 AzimB1Up - Azimuth value to use for I/O when blade 1 points up (degrees)
---------------------- MASS AND INERTIA ----------------------------------------
0.0 YawBrMass - Yaw bearing mass (kg)
240.00E3 NacMass - Nacelle mass (kg)
56.78E3 HubMass - Hub mass (kg)
0.0 TipMass(1) - Tip-brake mass, blade 1 (kg)
0.0 TipMass(2) - Tip-brake mass, blade 2 (kg)
0.0 TipMass(3) - Tip-brake mass, blade 3 (kg) [unused for 2 blades]
2607.89E3 NacYIner - Nacelle inertia about yaw axis (kg m^2)
534.116 GenIner - Generator inertia about HSS (kg m^2)
115.926E3 HubIner - Hub inertia about rotor axis [3 blades] or teeter axis [2 blades] (kg m^2)
---------------------- DRIVETRAIN ----------------------------------------------
100.0 GBoxEff - Gearbox efficiency (%)
94.4 GenEff - Generator efficiency [ignored by the Thevenin and user-defined generator models] (%)
97.0 GBRatio - Gearbox ratio (-)
False GBRevers - Gearbox reversal {T: if rotor and generator rotate in opposite directions} (flag)
28.1162E3 HSSBrTqF - Fully deployed HSS-brake torque (N-m)
0.6 HSSBrDT - Time for HSS-brake to reach full deployment once initiated (sec) [used only when HSSBrMode=1]
"Dummy" DynBrkFi - File containing a mech-gen-torque vs HSS-speed curve for a dynamic brake [CURRENTLY IGNORED] (quoted string)
867.637E6 DTTorSpr - Drivetrain torsional spring (N-m/rad)
6.215E6 DTTorDmp - Drivetrain torsional damper (N-m/(rad/s))
---------------------- SIMPLE INDUCTION GENERATOR ------------------------------
9999.9 SIG_SlPc - Rated generator slip percentage (%) [used only when VSContrl=0 and GenModel=1]
9999.9 SIG_SySp - Synchronous (zero-torque) generator speed (rpm) [used only when VSContrl=0 and GenModel=1]
9999.9 SIG_RtTq - Rated torque (N-m) [used only when VSContrl=0 and GenModel=1]
9999.9 SIG_PORt - Pull-out ratio (Tpullout/Trated) (-) [used only when VSContrl=0 and GenModel=1]
---------------------- THEVENIN-EQUIVALENT INDUCTION GENERATOR -----------------
9999.9 TEC_Freq - Line frequency [50 or 60] (Hz) [used only when VSContrl=0 and GenModel=2]
9998 TEC_NPol - Number of poles [even integer > 0] (-) [used only when VSContrl=0 and GenModel=2]
9999.9 TEC_SRes - Stator resistance (ohms) [used only when VSContrl=0 and GenModel=2]
9999.9 TEC_RRes - Rotor resistance (ohms) [used only when VSContrl=0 and GenModel=2]
9999.9 TEC_VLL - Line-to-line RMS voltage (volts) [used only when VSContrl=0 and GenModel=2]
9999.9 TEC_SLR - Stator leakage reactance (ohms) [used only when VSContrl=0 and GenModel=2]
9999.9 TEC_RLR - Rotor leakage reactance (ohms) [used only when VSContrl=0 and GenModel=2]
9999.9 TEC_MR - Magnetizing reactance (ohms) [used only when VSContrl=0 and GenModel=2]
---------------------- PLATFORM ------------------------------------------------
2 PtfmModel - Platform model {0: none, 1: onshore, 2: fixed bottom offshore, 3: floating offshore} (switch)
"NRELOffshrBsline5MW_Platform_Monopile_RF.dat" PtfmFile - Name of file containing platform properties (quoted string) [unused when PtfmModel=0]
---------------------- TOWER ---------------------------------------------------
99 TwrNodes - Number of tower nodes used for analysis (-)
"NRELOffshrBsline5MW_Tower_Monopile_RF.dat" TwrFile - Name of file containing tower properties (quoted string)
---------------------- NACELLE-YAW ---------------------------------------------
9028.32E6 YawSpr - Nacelle-yaw spring constant (N-m/rad)
19.16E6 YawDamp - Nacelle-yaw damping constant (N-m/(rad/s))
0.0 YawNeut - Neutral yaw position--yaw spring force is zero at this yaw (degrees)
---------------------- FURLING -------------------------------------------------
False Furling - Read in additional model properties for furling turbine (flag)
"Dummy" FurlFile - Name of file containing furling properties (quoted string) [unused when Furling=False]
---------------------- ROTOR-TEETER --------------------------------------------
0 TeetMod - Rotor-teeter spring/damper model {0: none, 1: standard, 2: user-defined from routine UserTeet} (switch) [unused for 3 blades]
0.0 TeetDmpP - Rotor-teeter damper position (degrees) [used only for 2 blades and when TeetMod=1]
0.0 TeetDmp - Rotor-teeter damping constant (N-m/(rad/s)) [used only for 2 blades and when TeetMod=1]
0.0 TeetCDmp - Rotor-teeter rate-independent Coulomb-damping moment (N-m) [used only for 2 blades and when TeetMod=1]
0.0 TeetSStP - Rotor-teeter soft-stop position (degrees) [used only for 2 blades and when TeetMod=1]
0.0 TeetHStP - Rotor-teeter hard-stop position (degrees) [used only for 2 blades and when TeetMod=1]
0.0 TeetSSSp - Rotor-teeter soft-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
0.0 TeetHSSp - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
---------------------- TIP-BRAKE -----------------------------------------------
0.0 TBDrConN - Tip-brake drag constant during normal operation, Cd*Area (m^2)
0.0 TBDrConD - Tip-brake drag constant during fully-deployed operation, Cd*Area (m^2)
0.0 TpBrDT - Time for tip-brake to reach full deployment once released (sec)
---------------------- BLADE ---------------------------------------------------
"NRELOffshrBsline5MW_Blade.dat" BldFile(1) - Name of file containing properties for blade 1 (quoted string)
"NRELOffshrBsline5MW_Blade.dat" BldFile(2) - Name of file containing properties for blade 2 (quoted string)
"NRELOffshrBsline5MW_Blade.dat" BldFile(3) - Name of file containing properties for blade 3 (quoted string) [unused for 2 blades]
---------------------- AERODYN -------------------------------------------------
"NRELOffshrBsline5MW_AeroDyn.ipt" ADFile - Name of file containing AeroDyn input parameters (quoted string)
---------------------- NOISE ---------------------------------------------------
"Dummy" NoiseFile - Name of file containing aerodynamic noise input parameters (quoted string) [used only when CompNoise=True]
---------------------- ADAMS ---------------------------------------------------
"NRELOffshrBsline5MW_ADAMSSpecific.dat" ADAMSFile - Name of file containing ADAMS-specific input parameters (quoted string) [unused when ADAMSPrep=1]
---------------------- LINEARIZATION CONTROL -----------------------------------
"NRELOffshrBsline5MW_Linear.dat" LinFile - Name of file containing FAST linearization parameters (quoted string) [unused when AnalMode=1]
---------------------- OUTPUT --------------------------------------------------
NRELOffshrBsline5MW_AeroDyn.ipt
NREL 5.0 MW offshore baseline aerodynamic input properties; Compatible with AeroDyn v12.58.
SI SysUnits - System of units used for input and output [must be SI for FAST] (unquoted string)
BEDDOES StallMod - Dynamic stall included [BEDDOES or STEADY] (unquoted string)
USE_CM UseCm - Use aerodynamic pitching moment model? [USE_CM or NO_CM] (unquoted string)
EQUIL InfModel - Inflow model [DYNIN or EQUIL] (unquoted string)
SWIRL IndModel - Induction-factor model [NONE or WAKE or SWIRL] (unquoted string)
0.005 AToler - Induction-factor tolerance (convergence criteria) (-)
PRANDtl TLModel - Tip-loss model (EQUIL only) [PRANDtl, GTECH, or NONE] (unquoted string)
PRANDtl HLModel - Hub-loss model (EQUIL only) [PRANdtl or NONE] (unquoted string)
"TurbSim.wnd" WindFile - Name of file containing wind data (quoted string)
90.0 HH - Wind reference (hub) height [TowerHt+Twr2Shft+OverHang*SIN(ShftTilt)] (m)
0.0 TwrShad - Tower-shadow velocity deficit (-)
9999.9 ShadHWid - Tower-shadow half width (m)
9999.9 T_Shad_Refpt - Tower-shadow reference point (m)
1.225 AirDens - Air density (kg/m^3)
1.464E-5 KinVisc - Kinematic air viscosity [CURRENTLY IGNORED] (m^2/sec)
0.02479 DTAero - Time interval for aerodynamic calculations (sec)
8 NumFoil - Number of airfoil files (-)
"AeroData\Cylinder1.dat" FoilNm - Names of the airfoil files [NumFoil lines] (quoted strings)
"AeroData\Cylinder2.dat"
"AeroData\DU40_A17.dat"
"AeroData\DU35_A17.dat"
"AeroData\DU30_A17.dat"
"AeroData\DU25_A17.dat"
"AeroData\DU21_A17.dat"
"AeroData\NACA64_A17.dat"
17 BldNodes - Number of blade nodes used for analysis (-)
RNodes AeroTwst DRNodes Chord NFoil PrnElm
2.8667 13.308 2.7333 3.542 1 NOPRINT
5.6000 13.308 2.7333 3.854 1 NOPRINT
8.3333 13.308 2.7333 4.167 2 NOPRINT
11.7500 13.308 4.1000 4.557 3 NOPRINT
15.8500 11.480 4.1000 4.652 4 NOPRINT
19.9500 10.162 4.1000 4.458 4 NOPRINT
24.0500 9.011 4.1000 4.249 5 NOPRINT
28.1500 7.795 4.1000 4.007 6 NOPRINT
32.2500 6.544 4.1000 3.748 6 NOPRINT
36.3500 5.361 4.1000 3.502 7 NOPRINT
40.4500 4.188 4.1000 3.256 7 NOPRINT
44.5500 3.125 4.1000 3.010 8 NOPRINT
48.6500 2.319 4.1000 2.764 8 NOPRINT
52.7500 1.526 4.1000 2.518 8 NOPRINT
56.1667 0.863 2.7333 2.313 8 NOPRINT
58.9000 0.370 2.7333 2.086 8 NOPRINT
61.6333 0.106 2.7333 1.419 8 NOPRINT
For a parked simulation with the blades feathered, I would expect the aerodynamic loads on the rotor to be quite small, unless there is sizeable yaw error. In this case, the gravity load may dominate the blade loading, and with the different azimuth angles between the three blades, differences in the blade loads would be expected.
Please note that to model a parked rotor, we typically recommend disabling the induction and unsteady airfoil aerodynamics models, i.e., StallMod = STEADY and IndModel = NONE in FAST v7.
I am using FAST v7 and OpenFAST to calculate the force distribution along the blade of NREL 5MW monopile-supported offshore wind turbine (OWT), and some errors confused me a lot.
(1) The parked OWT subjected to wind speed of V=42.0m/s was simulated based on FAST v7, and the blades were feathered. In addition, the yaw error, azimuth angle of blade 1 and rotor speed were set zero.
The induction and unsteady airfoil dynamics models were disabled (i.e., StallMod = STEADY and IndModel = NONE).
As shown in Fig.1 and 2, there is still a big difference between the distribution of shear force and bending moment of blade 2 and blade 3. Why is that?
(2) The monopile-supported OWT in operational case was simulated based on OpenFAST, and the downloaded files have not been modified. As shown in Fig. 3 and 4, some errors occured when running OpenFAST. How to solve this problem?
Regarding (1), I would guess the differences in the blade loads is due to the different contribution of gravity to the load, based on the azimuth orientation of the rotor. Shear, tilt, or skew in the flow due to yaw error could also contribute to differences in the loads between blades.
Regarding (2), did you change anything in the r-test model of the NREL 5-MW baseline wind turbine atop the monopile, e.g., initial conditions or time step?
Thanks for your kind help.
I can’t understand your explanation that the load difference between blade 2 and blade 3 is due to the contribution of gravity, the effect of gravity on blade 2 and blade 3 should be roughly equal according to the azimuth orientation of the rotor presented in Fig. 1. And I agree with you that the gravity is the main factor for the load difference between blade 1 and blade 2 (or blade 3). Additionally, I calculated the load of three blades with steady inflow wind. As shown in Fig.2, there is still a significant load difference between blade 2 and blade 3. How to explain this phenomenon?
While the aerodynamic loads in this parked condition are likely small, there are not zero, and will be impacted by the local angle of attack, which are different between the blades due to twist. Also, you haven’t said if there is any yaw error.
You could always isolate the contribution of various terms, e.g., by toggling gravity on/off, disabling/enabling structural DOFs, zeroing-out or keeping the aerodynamic twist, etc.
I am sorry for not stating clearly. I compiled OpenFAST v3.3.0 and controller DLL myself, and I got 1 skipped. (Visual studio 2017, Intel Fortran 2019)
Looking forward to your reply. Thanks again!
fatal: not a git repository (or any of the parent directories): .git
usually comes if you downloaded the source code from a zip file instead of cloning from GitHub. It shouldn’t cause any problem other than that the git hash/version number will be incorrect when you run the executable.
The Skipped warning just indicates that you have not selected to build the OpenFAST-Simulink interface.
