Fast errors for extreme load cases

Wind & Water Computer-Aided Engineering Software Tools
1

Dear all,

I am currently using FAST v7 to model the response of NREL 5MW offshore wind turbine under special extreme cases, in which the turbine is loss of network (idling) and the yaw and pitch systems both are out of control. The possible yaw misalignment and pitch angles are ±180° and 0-90°，respectively. The wind and wave parameters are: U=40m/s, TI=11%, Hs=8m, Tp=11s. The settings related to the yaw and pitch system in the main input files are following Dr. Jonkman’s recommendations in other forum topics.

When I run these simulations, I got the following error for the cases where pitch angle=0 (other cases, i.e. pitch angle>0, run normally). I really appreciate it if someone could help me to solve this problem. The main input file for yaw angle=60, pitch angle=0 is attached for your further check.

Best regards,
Patrick

[code]--------------------------------------------------------------------------------
------- 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 --------------------------------------
False 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)
0.001 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)
0.0 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]
1 HSSBrMode - HSS brake model {1: simple, 2: user-defined from routine UserHSSBr} (switch)
9999.9 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)
60 NacYawF - Final yaw angle for override yaw maneuvers (degrees)
9999.9 TPitManS(1) - Time to start override pitch maneuver for blade 1 and end standard pitch control (s)
9999.9 TPitManS(2) - Time to start override pitch maneuver for blade 2 and end standard pitch control (s)
9999.9 TPitManS(3) - Time to start override pitch maneuver for blade 3 and end standard pitch control (s) [unused for 2 blades]
9999.9 TPitManE(1) - Time at which override pitch maneuver for blade 1 reaches final pitch (s)
9999.9 TPitManE(2) - Time at which override pitch maneuver for blade 2 reaches final pitch (s)
9999.9 TPitManE(3) - Time at which override pitch maneuver for blade 3 reaches final pitch (s) [unused for 2 blades]
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 BlPitchF(1) - Blade 1 final pitch for pitch maneuvers (degrees)
0 BlPitchF(2) - Blade 2 final pitch for pitch maneuvers (degrees)
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)
True GenDOF - Generator DOF (flag)
True 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)
60 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 ----------------------------------------------
60.0 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)
“DLC6.2-yaw=60-Angle=0_1-Platform_Fixed.dat” PtfmFile - Name of file containing platform properties (quoted string) [unused when PtfmModel=0]
---------------------- TOWER ---------------------------------------------------
108 TwrNodes - Number of tower nodes used for analysis (-)
“NRELOffshrBsline5MW_Tower_Monopile_RF_Fixed.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))
60 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, CdArea (m^2)
0.0 TBDrConD - Tip-brake drag constant during fully-deployed operation, CdArea (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 -------------------------------------------------
“DLC6.2-yaw=60-Angle=0_1-AeroDyn_Fixed.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 --------------------------------------------------
True SumPrint - Print summary data to “.fsm” (flag)
1 OutFileFmt - Format for tabular (time-marching) output files (1: text file[.out], 2: Binary file [.outb], 3: both) (switch)
True TabDelim - Generate a tab-delimited tabular output file. (flag)
“ES10.3E2” OutFmt - Format used for tabular output except time. Resulting field should be 10 characters. (quoted string) [not checked for validity!]
30.0 TStart - Time to begin tabular output (s)
50 DecFact - Decimation factor for tabular output {1: output every time step} (-)
1.0 SttsTime - Amount of time between screen status messages (sec)
-3.09528 NcIMUxn - Downwind distance from the tower-top to the nacelle IMU (meters)
0.0 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)
1.912 ShftGagL - Distance from rotor apex [3 blades] or teeter pin [2 blades] to shaft strain gages [positive for upwind rotors] (meters)
9 NTwGages - Number of tower nodes that have strain gages for output [0 to 9] (-)
1,21,41,51,61,71,81,91,108 TwrGagNd - List of tower nodes that have strain gages [1 to TwrNodes] (-) [unused if NTwGages=0]
0 NBlGages - Number of blade nodes that have strain gages for output [0 to 9] (-)
5,9,13 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 OutList.txt for a listing of available output channels, (-)
“WindVxi , WindVyi , WindVzi” - Longitudinal, lateral, and vertical wind speeds
“WaveElev” - Wave elevation at the platform reference point
“RotSpeed , GenSpeed” - Low-speed shaft and high-speed shaft speeds
“TTDspFA , TTDspSS” - Tower fore-aft and side-to-side displacements
“PtchPMzc1, PtchPMzc2, PtchPMzc3” - Pitch angle
“TwrBsFxt , TwrBsFyt , TwrBsFzt” - Fore-aft shear, side-to-side shear, and vertical forces at the mudline
“TwrBsMxt , TwrBsMyt , TwrBsMzt” - Side-to-side bending, fore-aft bending, and yaw moments at the mudline
“PtfmSurge, PtfmSway , PtfmRoll , PtfmPitch” - Platform surge, sway, roll, and pitch displacements (for use in calculating in Crunch the tower-top displacements in the inertia frame)
“YawBrFxp , YawBrFyp , YawBrFzp” - Fore-aft shear, side-to-side shear, and vertical forces at the top of the tower (not rotating with nacelle yaw)
“YawBrMxp , YawBrMyp , YawBrMzp” - Side-to-side bending, fore-aft bending, and yaw moments at the top of the tower (not rotating with nacelle yaw)
“TwHt1FLxt, TwHt1MLyt, TwHt1TDxt” - Local side-to-side and fore-aft bending moments at tower gage
“TwHt2FLxt, TwHt2MLyt, TwHt2TDxt”
“TwHt3FLxt, TwHt3MLyt, TwHt3TDxt”
“TwHt4FLxt, TwHt4MLyt, TwHt4TDxt”
“TwHt5FLxt, TwHt5MLyt, TwHt5TDxt”
“TwHt6FLxt, TwHt6MLyt, TwHt6TDxt”
“TwHt7FLxt, TwHt7MLyt, TwHt7TDxt”
“TwHt8FLxt, TwHt8MLyt, TwHt8TDxt”
“TwHt9FLxt, TwHt9MLyt, TwHt9TDxt”
“RootFxb1, RootFyb1, RootMxb1,RootMyb1” -flapwise/edgewise force or moment at blade root
“YawPzn” -Nacelle yaw angle (deg)
END of FAST input file (the word “END” must appear in the first 3 columns of this last line).

[/code]

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2

Dear Patrick,

Well, it looks like your model has gone numerically unstable, but I’m not sure why.

You haven’t shared your AeroDyn input file, but have you disabled the wake calculation and unsteady airfoil aerodynamic calculation as recommend for an idling condition?

Please note that the case you are running sounds very extreme, with four independent failures (loss of control of each of the three blades and loss of yaw control), which is beyond the requirements of IEC design standards.

Please also note that FAST v7 is now quite old; I would generally recommend upgrading to the newest version of FAST (now OpenFAST), unless you have a strong reason to run this older version.

Best regards,

3

Dear Jason,

Thanks a lot for your response.

I have posted the AeroDyn input file as follows, but I am not sure which parameters should be reset to disable the wake calculation and unsteady airfoil aerodynamic calculation. It seems there are no direct options like WakeMod and AFAeroMod in FAST v7.

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) DYNIN InfModel - Inflow model [DYNIN or EQUIL] (unquoted string) WAKE 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) "DLC6.1-U=42_9.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

Indeed, the case I am running is very extreme, and as you pointed out, is beyond the requirements of IEC design standards. This extreme case is more related to typhoon conditions. During a typhoon event, the direction of the typhoon can change dramatically during several hours, however, the yaw and pitch system cannot always follow it as the power has been cut off, leading to varied combinations of yaw and pitch angle.

Thank you for your kind reminder. The reason I use FAST v7 is that I’d like to model soil-structure interaction. Through comparing, I found the FAST v7 is the most optimal version to achieve this.

Looking very forward to your reply.

Best regards,
Patrick

4

Dear Patrick,

To disable the wake and unsteady airfoil aerodynamic calculations in AeroDyn v12.58, set StallMod = STEADY and IndModel = NONE. Not using these settings may be the cause of the instability you are seeing.

Which soil-structure interaction model are you using in FAST v7? You may be interested to know that a coupled springs (CS) model has been introduced into SubDyn, recently merged into the dev branch of OpenFAST–see: github.com/OpenFAST/openfast/pull/537.

Best regards,

5

Dear Jason,

Thanks a lot for your reply. Following your suggestion, I have set StallMod = STEADY and IndModel = NONE, but I get another error, as shown in the figure.

Glad to hear that CS model is already available in OpenFAST, but in my case, I am going to use a more advanced model, such as p-y model and other multi-spring models, to better reflect the pile-soil interaction. Implementing such a model in FAST v7 is more straightforward to me than in other versions of FAST.

I look forward to your reply.

Best regards,
Patrick

error.jpg
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6

Dear Patrick,

You’ve already disabled the wake calculation, but to eliminate this error, it may help to also set InfModel = EQUIL.

Best regards,

7

Dear Jason,

Thanks for your comments. It goes well now.

Best regards,
Patrick

8

Dear Jason,

I am using a DS model to simulate the response of the 5MW offshore wind turbine. The wind and wave parameters are U=12m/s, Hs=3 m, Tp=8 s. Two conditions, namely operating and idling, are modeled.

From the results, I found that the oscillation of the moment at the mudline when the turbine is idling is much larger (up to 2 times) than that when the turbine is operating. But when I change the DS model to the default foundation modeling type in FAST, i.e., fixed base, the oscillations of the moment at the mudline between these two conditions are comparable. I am really puzzled at it and I’d like to seek your wisdom.

Thanks in advance.

Best regards,
Patrick

9

Dear Patrick,

Can you clarify which version of FAST you are using (are you stilling using FAST v7, as in the posts above) and how you are implementing the distributed springs (DS) model? Are these the standard fixed and DS models of the NREL 5-MW turbine atop the OC3-monopile in FAST v7 that are available on this forum?

Best regards,

10

Dear Jason,

Yes. I am using FASTv7. 02. The DS model is developed in light of the one you shared on this forum for OC3-monopile. I just changed the pile length below the ground surface and the values of pile-soil stiffness in UserTwrLd to fit in my case. The tower properties and the mode shape fitting parameters were also updated accordingly. For the fixed model, I used the default one without any change.

Looking forward to your reply.

Best regards,
Patrick

11

Dear Patrick,

I would expect that the idling situation would result in larger oscillations in mudline moment due to the limited aerodynamic damping in the idling condition relative to the operational condition. If I understand correctly, it sounds like you are only seeing this when modeling soil-pile interaction through the DS model…is that correct?

I’m curious if this tied to your customized model or if you see the same trend for the original model of the NREL 5-MW baseline turbine atop the OC3-monopile + DS model?

Best regards,

12

Dear Jason,

I also see the same trend using the original model of the NREL 5-MW baseline turbine atop the OC3-monopile + DS model (using the intact files you shared).

Indeed, I fully agree with you this can be attributed to the highly reduced aerodynamic damping in the idling condition. But how to quantitatively evaluate the aerodynamic damping in both idling and operating conditions?

Why we cannot observe a similar trend when the tower base is fixed (without considering pile-soil interaction) in the idling condition? The aerodynamic damping I think is also reduced for the fixed base model.

Best regards,
Patrick

13

Dear Patrick,

I generally agree with your comments and I’m not sure I know why you are not seeing the same effect with the rigid foundation. I have not used these FAST v7 models in many years. It may be worth to upgrade to OpenFAST to see if the same trends exist in the newest version of the software, but that would take some effort and the DS model is not as straightforward to implement (the effect for rigid foundation could be straightforwardly checked though).

The level of damping in the various full-system modes (e.g., first bending mode of the support structure) in both idling and operating conditions can be quantified through a linearization analysis or from tower free-decay simulations. But for the operating condition, the aerodynamic linearization of OpenFAST is much improved over that of FAST v7.

Best regards,

14

Dear Jason,

Thanks a lot for your valuable comments. I’ll have a further check in Openfast and do some free-decay simulations to quantify the aerodynamic damping.

Best regards,
Patrick

15

Dear Jason,

As suggested, I use Openfast instead of FAST7 to simulate the fixed-base offshore wind turbine under both idling and operating conditions. But the trend is similar to that calculated by FAST7. That is, smaller oscillations in mudline moment are observed in the idling condition relative to the operational condition. So wired.

Due to the limited aerodynamic damping in the idling condition, the oscillations in mudline moment are supposed to be larger than that in the operating condition. I was wondering if you have proper explanations for this trend.

Best regards,
Patrick

16

Dear Patrick,

OK, thanks for confirming. Can you describe the conditions you are simulating in OpenFAST, or better yet, share your OpenFAST input and output files for the simulations with idling and operating conditions, so, that I can better understand what you are simulating and the results you are obtaining?

Best regards,

17

Dear Jason,

Thank you for your quick reply.

Actually, I know little about Openfast, so I asked my colleague who has experience with it to run the simulations for me. I have sent him a message to ask for the input and output files. I’ll share the files once I get them.

Before that, I’d like to share you with the typical FAST7 input and output files that I have for the simulations with idling and operating conditions. Maybe you can have a quick check first. The wind and wave parameters for both conditions are the same: U=24 m/s, Hs= 3.42m, Tp=7.8. The trend is also observed for other wind and wave conditions.

Best regards,
Patrick
Part2.zip (1.34 MB)
Part1.zip (3.23 MB)

18

Dear Jason,

Enclosed please find the Openfast input and output files for both conditions. Thanks in advance.

Best regards,
Patrick
idlingTests.zip (1.82 MB)

19

Dear Patrick,

I looked briefly at your OpenFAST input files; just a couple comments:

  • The aerodynamic excitation is much less for the parked case because the blades are feathered to 90 degrees, which greatly reduces the aerodynamic thrust on the rotor compared to the operating case. So, your results make sense to me, with much less excitation in the parked case.
  • From my quick look at your OpenFAST input files, everything looks set up correctly except that you are using the same AeroDyn input file for the operating and parked cases. You haven’t shared your AeroDyn v15 input file, but I would expect the following inputs to be different between the operating and parked cases: WakeMod = 1 or 2 (operating) and WakeMod = 0 (parked); AFAeroMod = 1 or 2 (operating) and AFAeroMod = 1 (parked).

Best regards,

20

Dear Jason,

Thanks a lot for your reply.

Yes. I have already disabled the wake calculation in the idling condition.

Best regards,
Patrick