Linearization of the NREL 5MW-OC4-DeepCwind SemiSubmersible wind turbine

Dear Dr. Jonkman,

I am now working on control of the NREL 5 MW - OC4-
DeepCwind SemiSubmersible wind turbine. I was wondering whether I can obtain a linearized model for this wind turbine including the semi-submersible platform at different wind speed conditions in FAST. I tried this in FAST v7.02.00d-bjj with the following fst file but failed and got the error message that “TwrNodes must not be less than 1”. However, the “TwrNodes” is set to be 20 in the fst file.

--------------------------------------------------------------------------------
------- FAST INPUT FILE --------------------------------------------------------
NREL 5.0 MW Baseline Wind Turbine OC4
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)
   2       AnalMode    - Analysis mode {1: Run a time-marching simulation, 2: create a periodic linearized model} (switch)
   3        NumBl       - Number of blades (-)
 500     TMax        - Total run time (s)
  0.0125   DT          - Integration time step (s) 0.0125
---------------------- TURBINE CONTROL -----------------------------------------
   0        YCMode      - Yaw control mode {0: none, 1: user-defined from routine UserYawCont, 2: user-defined from Simulink} (switch)
0 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]
   1        VSContrl    - Variable-speed control mode {0: none, 1: simple VS, 2: user-defined from routine UserVSCont, 3: user-defined from Simulink} (switch)
1.1737e+03 9999.9e-9   VS_RtGnSp   - Rated generator speed for simple variable-speed generator control (HSS side) (rpm) [used only when VSContrl=1]
43093.55   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]
9999.9e-9 .0255764 9999.9e-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]
9999.9e-9 10 9999.9e-9   VS_SlPc     - Rated generator slip percentage in Region 2 1/2 for simple variable-speed generator control (%) [used only when VSContrl=1]
   1        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]
   0.0      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)
   0.0      NacYawF     - Final yaw angle for 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]
-8.1885 15.11 17.638503882818796 14.842799930247352 15.0976 15.1762 18.1936      BlPitch(1)  - Blade 1 initial pitch (degrees)
-8.1885 15.11 17.638503882818796 14.842799930247352 15.0976 15.1762 18.1936      BlPitch(2)  - Blade 2 initial pitch (degrees)
-8.1885 15.11 17.638503882818796 14.842799930247352 15.0976 15.1762 18.1936      BlPitch(3)  - Blade 3 initial pitch (degrees)
   0.0      B1PitchF(1) - Blade 1 final pitch for pitch maneuvers (degrees)
   0.0      B1PitchF(2) - Blade 2 final pitch for pitch maneuvers (degrees)
   0.0      B1PitchF(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 -------------------------------------------
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)
F            GenDOF      - Generator DOF (flag)
T        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)
T           CompAero    - Compute aerodynamic forces (flag)
F           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)
12.13      RotSpeed    - Initial or fixed rotor speed (rpm)
  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 (%)
 94 100 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]
            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 ------------------------------------------------
   3        PtfmModel   - Platform model {0: none, 1: onshore, 2: fixed bottom offshore, 3: floating offshore} (switch)
"OC4Semi_Modeling_PlatformLin.dat"           PtfmFile    - Name of file containing platform properties (quoted string) [unused when PtfmModel=0]
"Added_Damping.dat"  				 PtfmAddFile
0                Kx          - Surge stiffness
0                Ky          - Sway stiffness
0                Kz          - Heave stiffness
0                Kp          - Roll stiffness
0                Kq          - Pitch stiffness
0                Kr          - Yaw stiffness
0                Bx          - Surge damping
0                By          - Sway damping
0                Bz          - Heave damping
0                Bp          - Roll damping
0                Bq          - Pitch damping
0                Br          - Yaw damping
395000           Bx_quad     - Quadratic Surge damping
395000  		     By_quad     - Quadratic Sway damping
3880000  		  Bz_quad     - Quadratic Heave damping
37000000000		  Bp_quad     - Quadratic Roll damping
37000000000 	  Bq_quad     - Quadratic Pitch damping
4080000000  	  Br_quad     - Quadratic Yaw damping
---------------------- TOWER ---------------------------------------------------
20        TwrNodes    - Number of tower nodes used for analysis (-)
"NRELOffshrBsline5MW_Tower_OC4DeepCwindSemi.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)
            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"                  BldFile1    - Name of file containing properties for blade 1 (quoted string)
"NRELOffshrBsline5MW_Blade.dat"                  BldFile2    - Name of file containing properties for blade 2 (quoted string)
"NRELOffshrBsline5MW_Blade.dat"                  BldFile3    - Name of file containing properties for blade 3 (quoted string) [unused for 2 blades]
---------------------- AERODYN -------------------------------------------------
"OC4Semi_Modeling_AerodynLin.ipt"                ADFile      - Name of file containing AeroDyn input parameters (quoted string)
---------------------- NOISE ---------------------------------------------------
            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 -----------------------------------
"OC4Semi_LinearR3.dat"                 LinFile     - Name of file containing FAST linearization parameters (quoted string) [unused when AnalMode=1]
---------------------- OUTPUT --------------------------------------------------
True        SumPrint    - Print summary data to "<RootName>.fsm" (flag)1
1           OutFileFmt  - Format for tabular (time-marching) output file(s) (1: text file [<RootName>.out], 2: binary file [<RootName>.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!]
  0.0   TStart      - Time to begin tabular output (s)
   1        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)
   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 OutList.txt for a listing of available output channels, (-)			
"WindVxi  , WindVyi  , WindVzi"                              - Longitudinal, lateral, and vertical wind speeds
"WaveElev"
"Wave1Vxi , Wave1Vyi , Wave1Vzi"
"Wave2Vxi , Wave2Vyi , Wave2Vzi"
"Wave3Vxi , Wave3Vyi , Wave3Vzi"
"Wave4Vxi , Wave4Vyi , Wave4Vzi"
"LSShftFxa,LSShftFys,LSShftFzs"
"GenPwr   , GenTq"                                           - Electrical generator power and torque
"Azimuth"                                                    - Blade 1 azimuth angle
"RotSpeed , GenSpeed"                                        - Low-speed shaft and high-speed shaft speeds
"OoPDefl1 , IPDefl1  , TwstDefl1"                            - Blade 1 out-of-plane and in-plane deflections and tip twist
"BldPitch1"                                                  - Pitch angles for blade 1
"TTDspFA , TTDspSS  , TTDspTwst"                            - Tower fore-aft and side-to-side displacements and top twist
"PtfmSurge, PtfmSway , PtfmHeave"                            - Platform translational surge, sway, and heave displacements
"PtfmTVxi , PtfmTVyi , PtfmTVzi"                             - Platform translational surge, sway, and heave velocity (m/s)
"PtfmRoll , PtfmPitch, PtfmYaw"                              - Platform rotational roll, pitch and yaw displacements
"PtfmRVxi , PtfmRVyi, PtfmRVzi"
"PtfmRAxi , PtfmRAyi , PtfmRAzi"
"RootFxc1 , RootFyc1 , RootFzc1"                             - Out-of-plane shear, in-plane shear, and axial forces at the root of blade 1
"RootMxc1 , RootMyc1 , RootMzc1"                             - In-plane bending, out-of-plane bending, and pitching moments at the root of blade 1
"RootMEdg1, RootMFlp1"                                       - Edgewise and flapwise bending moments at the root of blade 1
"RotTorq  , LSSGagMya, LSSGagMza"                            - Rotor torque and low-speed shaft 0- and 90-rotating bending moments at the main bearing
"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)
"TwrBsFxt , TwrBsFyt , TwrBsFzt"                             - Fore-aft shear, side-to-side shear, and vertical forces at the base of the tower (platform)
"TwrBsMxt , TwrBsMyt , TwrBsMzt"                             - Side-to-side bending, fore-aft bending, and yaw moments at the base of the tower (platform)
"RotFurlP , RotFurlP , RotFurlP"                             					 - Platform forces sensors 45-47
"RotFurlP , RotFurlP , RotFurlP"                             					 - Platform forces sensors 48-50
"Fair1Ten , Fair2Ten , Fair3Ten"                             - Lines 1-3 fairlead tensions 
"Fair1Ang , Fair2Ang , Fair3Ang"                             - Lines 1-3 fairlead angles
"Anch1Ten , Anch2Ten , Anch3Ten"                             - Lines 1-3 anchor tensions 
"Anch1Ang , Anch2Ang , Anch3Ang"                             - Lines 1-3 anchor angles
"TipDxb1  , TipDyb1"
"TwHt1TDxt"
"PtfmFxt , PtfmFyt , PtfmFxi , PtfmFyi"
"RotCt , RotCp , RotCq"
"Q_Sg,Q_Sw,Q_Hv,Q_R,Q_P,Q_Y,Q_TFA1,Q_TSS1,Q_TFA2,Q_TSS2,Q_Yaw,Q_GeAz,Q_DrTr"
"Q_B1F1,Q_B2F1,Q_B3F1,Q_B1E1,Q_B2E1,Q_B3E1,Q_B1F2,Q_B2F2,Q_B3F2"
"QD_Sg,QD_Sw,QD_Hv,QD_R,QD_P,QD_Y,QD_TFA1,QD_TSS1,QD_TFA2,QD_TSS2,QD_Yaw,QD_GeAz,QD_DrTr"
"QD_B1F1,QD_B2F1,QD_B3F1,QD_B1E1,QD_B2E1,QD_B3E1,QD_B1F2,QD_B2F2,QD_B3F2"
"QD2_R,QD2_P,QD2_DrTr,HSShftPwr"
"LSSTipPxa,LSSTipVxa,LSSTipAxa"
"LSSGagPxa,LSSGagVxa,LSSGagAxa"
"HSShftV,HSShftA"
"OoPDefl1 , IPDefl1  , TwstDefl1"
"OoPDefl2 , IPDefl2  , TwstDefl2"
"OoPDefl3 , IPDefl3  , TwstDefl3"
"RotPwr, NacYaw"
"YawPzn"

END of FAST input file (the word "END" must appear in the first 3 columns of this last line).
--------------------------------------------------------------------------------

Thank you in advance.

Best,
Boran

Dear Boran,

From my quick review of your FAST v7 input file, I see that you have lines pertaining to inputs PtfmAddFile, Kx, …, Br_quad. But these are not standard input parameters in FAST v7. Have you customized the source code in some way to include these? (The addition of these input parameters is likely why FAST v7 cannot properly read the input file and is triggering an error regarding TwrNodes.)

While FAST v7 can be used to linearize floating offshore wind models, the hydrodynamic capability of FAST v7 is greatly simplified relative to FAST v8 (and FAST v7 cannot really be used to model the strip-theory members of the OC4-DeepCwind semisubmersible).

We at NREL are currently working on the extension of OpenFAST to enable full-system linaerization for floating offshore wind turbines, including the linearization of HydroDyn and MAP++.

Best regards,

Dear Dr. Jonkman,

Thanks very much for your quick reply. To answer your question, I got the files from one colleague in UBC Control Engineering Lab, who customized the fst file for OC4-DeepCwind semisubmersible under the direction of Dr. Alan Wright (I guess) at NREL. We can successfully run the simulation with the customized fst file but not for linearization.

Actually, I do not have to use FAST v7. If I use FAST v8, can I do the linearization for the OC4-DeepCwind semisubmersible? In addition, are the input files for OC4-DeepCwind semisubmersible included in FAST v8 installer? If not, where can I find them?

Another question, when using FAST v8 for offshore wind turbine linearization, can we get the wave disturbance matrix (Bw)? I heard from my colleagues that the wave disturbance matrix cannot be obtained in FAST v7 but I am not sure.

Thank you.

Best,
Boran

Dear Boran,

The OC4-DeepCwind semisubmersible is available as Test25 in the FAST v8 CertTest or as the “5MW_OC4Semi_WSt_WavesWN” test in the OpenFAST v1 r-test.

FAST v8 does not have linearization capability for floating offshore wind turbines. As I mentioned in my prior post, we are currently working on the extension of OpenFAST to enable full-system linaerization for floating offshore wind turbines, including the linearization of HydroDyn and MAP++. This functionality will include the ability to linearize the wave disturbance, which was not available in the linearization functionality of FAST v7.

Best regards,

Dear Dr. Jonkman,

Thanks for your further reply. I just want to double check one more thing. When you say “While FAST v7 can be used to linearize floating offshore wind models”, does it mean that FAST v7 can be used to linearize floating offshore wind turbine?

Regards
Boran

Dear Boran,

Yes, FAST v7 can be used to linearize floating offshore wind turbine models, but the linearization does not include the wave disturbance, radiation damping must be disabled, and the hydrodynamics capability in FAST v7 is less advanced than in FAST v8.

Best regards,

Dear Dr. Jonkman,

Thanks for your further clarification. Good to know that FAST v7 can be used to linearize offshore wind turbines. In that case, I still want to try linearize the OC4-DeepCwind SemiSubmersible (OC4 for short) in FAST v7. However, the standard test cases under the folder CertTest in FAST v7 do not include the one for OC4. As I mentioned before, I used a customized fst file for simulation of OC4 with additional parameters under the category “PLATFORM”, as shown below.

---------------------- PLATFORM ------------------------------------------------ 3 PtfmModel - Platform model {0: none, 1: onshore, 2: fixed bottom offshore, 3: floating offshore} (switch) "OC4Semi_Modeling_Platform.dat" PtfmFile - Name of file containing platform properties (quoted string) [unused when PtfmModel=0] "Added_Damping.dat" PtfmAddFile 0 Kx - Surge stiffness 0 Ky - Sway stiffness 0 Kz - Heave stiffness 0 Kp - Roll stiffness 0 Kq - Pitch stiffness 0 Kr - Yaw stiffness 0 Bx - Surge damping 0 By - Sway damping 0 Bz - Heave damping 0 Bp - Roll damping 0 Bq - Pitch damping 0 Br - Yaw damping 395000 Bx_quad - Quadratic Surge damping 395000 By_quad - Quadratic Sway damping 3880000 Bz_quad - Quadratic Heave damping 37000000000 Bp_quad - Quadratic Roll damping 37000000000 Bq_quad - Quadratic Pitch damping 4080000000 Br_quad - Quadratic Yaw damping ---------------------- TOWER --------------------------------------------------- 20 TwrNodes - Number of tower nodes used for analysis (-) "NRELOffshrBsline5MW_Tower_OC4DeepCwindSemi.dat" TwrFile - Name of file containing tower properties (quoted string)

As you suggested before, the additional parameters may cause trouble to the linearization procedure, which triggered the error regarding TwrNodes. I tried to delete those parameters in the fst file for LINEARIZATION and deactivated the radiation damping. However, the linearization process does not converge, as shown below. I was wondering whether this is related to removal of the additional parameters, especially those damping parameters, i.e. Bx_quad, By_quad, Bz_quad … . In addition, instead of removing those parameters (which means completely ignoring those parameters), do I have other ways for linearization of OC4?

Thank you for your suggestion. Look foward to your reply.

Best,
Boran

Beginning iteration to find a steady state solution of type:
 Constant speed (GenDOF = False)

             Avg Rotor    Nacelle  Generator      Blade   Dsplcmnt   Velocity
Iter    Time     Speed Yaw Demand     Torque      Pitch     2-norm     2-norm
Nmbr   (sec)     (rpm)      (deg)     (kN-m)      (deg)      (rad)    (rad/s)
-----------------------------------------------------------------------------
   1    4.95  12.12996    0.00000   43.09355   -8.18850  0.0085279  0.0030504
   2    9.89  12.12996    0.00000   43.09355   -8.18850  0.0153729  0.0006775
   3   14.84  12.12996    0.00000   43.09355   -8.18850  0.0053144  0.0034513
   4   19.79  12.12996    0.00000   43.09355   -8.18850  0.0126038  0.0021393
   5   24.73  12.12996    0.00000   43.09355   -8.18850  0.0138137  0.0016610
   6   29.68  12.12996    0.00000   43.09355   -8.18850  0.0035837  0.0033793
   7   34.62  12.12996    0.00000   43.09355   -8.18850  0.0134239  0.0011754
   8   39.57  12.12996    0.00000   43.09355   -8.18850  0.0096172  0.0024333
   9   44.52  12.12996    0.00000   43.09355   -8.18850  0.0058558  0.0029698
  10   49.46  12.12996    0.00000   43.09355   -8.18850  0.0139882  0.0002073
  11   54.41  12.12996    0.00000   43.09355   -8.18850  0.0069213  0.0028582
  12   59.36  12.12996    0.00000   43.09355   -8.18850  0.0097991  0.0022653
  13   64.30  12.12996    0.00000   43.09355   -8.18850  0.0129259  0.0009955
  14   69.25  12.12996    0.00000   43.09355   -8.18850  0.0025490  0.0029982
  15   74.20  12.12996    0.00000   43.09355   -8.18850  0.0108653  0.0015054
  16   79.14  12.12996    0.00000   43.09355   -8.18850  0.0101855  0.0017856
  17   84.09  12.12996    0.00000   43.09355   -8.18850  0.0045129  0.0027514
  18   89.04  12.12996    0.00000   43.09355   -8.18850  0.0123369  0.0005237
  19   93.98  12.12996    0.00000   43.09355   -8.18850  0.0077783  0.0022724
  20   98.93  12.12996    0.00000   43.09355   -8.18850  0.0070442  0.0022899
  21  103.87  12.12996    0.00000   43.09355   -8.18850  0.0115514  0.0005306
  22  108.82  12.12996    0.00000   43.09355   -8.18850  0.0032826  0.0025475
  23  113.77  12.12996    0.00000   43.09355   -8.18850  0.0085191  0.0016853
  24  118.71  12.12996    0.00000   43.09355   -8.18850  0.0102952  0.0011884
  25  123.66  12.12996    0.00000   43.09355   -8.18850  0.0044779  0.0024654
  26  128.61  12.12996    0.00000   43.09355   -8.18850  0.0104439  0.0008860
  27  133.55  12.12996    0.00000   43.09355   -8.18850  0.0079544  0.0017150
  28  138.50  12.12996    0.00000   43.09355   -8.18850  0.0043919  0.0021782
  29  143.45  12.12996    0.00000   43.09355   -8.18850  0.0098964  0.0004218
  30  148.39  12.12996    0.00000   43.09355   -8.18850  0.0045748  0.0020773
  31  153.34  12.12996    0.00000   43.09355   -8.18850  0.0067283  0.0017578
  32  158.29  12.12996    0.00000   43.09355   -8.18850  0.0100548  0.0007161
  33  163.23  12.12996    0.00000   43.09355   -8.18850  0.0051167  0.0021125
  34  168.18  12.12996    0.00000   43.09355   -8.18850  0.0084110  0.0011625
  35  173.12  12.12996    0.00000   43.09355   -8.18850  0.0076224  0.0012454
  36  178.07  12.12996    0.00000   43.09355   -8.18850  0.0022772  0.0019902
  37  183.02  12.12996    0.00000   43.09355   -8.18850  0.0082094  0.0006359
  38  187.96  12.12996    0.00000   43.09355   -8.18850  0.0055986  0.0015986
  39  192.91  12.12996    0.00000   43.09355   -8.18850  0.0055064  0.0016880
  40  197.86  12.12996    0.00000   43.09355   -8.18850  0.0092508  0.0004521
  41  202.80  12.12996    0.00000   43.09355   -8.18850  0.0054610  0.0017348
  42  207.75  12.12996    0.00000   43.09355   -8.18850  0.0062894  0.0013133
  43  212.70  12.12996    0.00000   43.09355   -8.18850  0.0069696  0.0009022
  44  217.64  12.12996    0.00000   43.09355   -8.18850  0.0022021  0.0017250
  45  222.59  12.12996    0.00000   43.09355   -8.18850  0.0068040  0.0008567
  46  227.54  12.12996    0.00000   43.09355   -8.18850  0.0062631  0.0011751
  47  232.48  12.12996    0.00000   43.09355   -8.18850  0.0049021  0.0015521
  48  237.43  12.12996    0.00000   43.09355   -8.18850  0.0080562  0.0005770
  49  242.37  12.12996    0.00000   43.09355   -8.18850  0.0055212  0.0013792
  50  247.32  12.12996    0.00000   43.09355   -8.18850  0.0044032  0.0013554
  51  252.27  12.12996    0.00000   43.09355   -8.18850  0.0061949  0.0007781
  52  257.21  12.12996    0.00000   43.09355   -8.18850  0.0037451  0.0014114
  53  262.16  12.12996    0.00000   43.09355   -8.18850  0.0058297  0.0009710
  54  267.11  12.12996    0.00000   43.09355   -8.18850  0.0063349  0.0008482
  55  272.05  12.12996    0.00000   43.09355   -8.18850  0.0045819  0.0013207
  56  277.00  12.12996    0.00000   43.09355   -8.18850  0.0064128  0.0007591
  57  281.95  12.12996    0.00000   43.09355   -8.18850  0.0051186  0.0010708
  58  286.89  12.12996    0.00000   43.09355   -8.18850  0.0032220  0.0012851
  59  291.84  12.12996    0.00000   43.09355   -8.18850  0.0055343  0.0008361
  60  296.78  12.12996    0.00000   43.09355   -8.18850  0.0051900  0.0011046
  61  301.73  12.12996    0.00000   43.09355   -8.18850  0.0054779  0.0010213
  62  306.68  12.12996    0.00000   43.09355   -8.18850  0.0059251  0.0007786
  63  311.62  12.12996    0.00000   43.09355   -8.18850  0.0044789  0.0010779
  64  316.57  12.12996    0.00000   43.09355   -8.18850  0.0046754  0.0009141
  65  321.52  12.12996    0.00000   43.09355   -8.18850  0.0045064  0.0008851
  66  326.46  12.12996    0.00000   43.09355   -8.18850  0.0033772  0.0011082
  67  331.41  12.12996    0.00000   43.09355   -8.18850  0.0050022  0.0009369
  68  336.36  12.12996    0.00000   43.09355   -8.18850  0.0059992  0.0008360
  69  341.30  12.12996    0.00000   43.09355   -8.18850  0.0054218  0.0009568
  70  346.25  12.12996    0.00000   43.09355   -8.18850  0.0049421  0.0008827
  71  351.20  12.12996    0.00000   43.09355   -8.18850  0.0043559  0.0008364
  72  356.14  12.12996    0.00000   43.09355   -8.18850  0.0033290  0.0009545
  73  361.09  12.12996    0.00000   43.09355   -8.18850  0.0038409  0.0008708
  74  366.03  12.12996    0.00000   43.09355   -8.18850  0.0043486  0.0008642
  75  370.98  12.12996    0.00000   43.09355   -8.18850  0.0047649  0.0010159
  76  375.93  12.12996    0.00000   43.09355   -8.18850  0.0061841  0.0007531
  77  380.87  12.12996    0.00000   43.09355   -8.18850  0.0055638  0.0008341
  78  385.82  12.12996    0.00000   43.09355   -8.18850  0.0036458  0.0010641
  79  390.77  12.12996    0.00000   43.09355   -8.18850  0.0043184  0.0007129
  80  395.71  12.12996    0.00000   43.09355   -8.18850  0.0033777  0.0008937
  81  400.66  12.12996    0.00000   43.09355   -8.18850  0.0033667  0.0009665
  82  405.61  12.12996    0.00000   43.09355   -8.18850  0.0052185  0.0005824
  83  410.55  12.12996    0.00000   43.09355   -8.18850  0.0046552  0.0010001
  84  415.50  12.12996    0.00000   43.09355   -8.18850  0.0055768  0.0008415
  85  420.45  12.12996    0.00000   43.09355   -8.18850  0.0055867  0.0006332
  86  425.39  12.12996    0.00000   43.09355   -8.18850  0.0022917  0.0011760
  87  430.34  12.12996    0.00000   43.09355   -8.18850  0.0042634  0.0007725
  88  435.28  12.12996    0.00000   43.09355   -8.18850  0.0046077  0.0007284
  89  440.23  12.12996    0.00000   43.09355   -8.18850  0.0033673  0.0011042
  90  445.18  12.12996    0.00000   43.09355   -8.18850  0.0056978  0.0004426
  91  450.12  12.12996    0.00000   43.09355   -8.18850  0.0047733  0.0009129
  92  455.07  12.12996    0.00000   43.09355   -8.18850  0.0043631  0.0010291
  93  460.02  12.12996    0.00000   43.09355   -8.18850  0.0055000  0.0004636
  94  464.96  12.12996    0.00000   43.09355   -8.18850  0.0020110  0.0011951
  95  469.91  12.12996    0.00000   43.09355   -8.18850  0.0041945  0.0009409
  96  474.86  12.12996    0.00000   43.09355   -8.18850  0.0059126  0.0004688
  97  479.80  12.12996    0.00000   43.09355   -8.18850  0.0037438  0.0011849
  98  484.75  12.12996    0.00000   43.09355   -8.18850  0.0055763  0.0006000
  99  489.69  12.12996    0.00000   43.09355   -8.18850  0.0050011  0.0007347
 100  494.64  12.12996    0.00000   43.09355   -8.18850  0.0026020  0.0011946

The solution does not appear to converge after 500 seconds!

Try increasing the total run time, TMax, increasing system damping values, or i
creasing the
convergence tolerances, DispTol and/or VelTol.
The linearized system matrices were not formed.

Aborting FAST.

Dear Boran,

I don’t know anything about your customized code, so, can’t really comment on how if/how linearization would work with it.

Certainly the standard version of FAST v7 can be used to linearize floating offshore wind turbine models, but as we’ve already discussed above, FAST v7 is limited in its capability for modeling the OC4-DeepCwind semisubmersible (hence your desire to customize it, I presume).

From your steady-state solution results, it appears that the displacement 2 norm is decreasing over time (rather than diverging), so you should be able to achieve a steady-state solution using one of three methods suggested in the message: increasing the total run time, TMax, increasing system damping values, or increasing the convergence tolerances, DispTol and/or VelTol.

Best regards,

Dear Dr. Jonkman,

Thanks very much for your further clarification and suggestion. Look forward to seeing the function of linearizing floating offshore wind turbines in FAST v8 and OpenFast.

Best,
Boran