FVW Simulation (OLAF Module): Surge motion + Rotor speed variation

[Laurens09]

Dear all,

I have created a FVW model of a wind turbine through the OLAF module of openfast. The WT platform oscillates in the surge direction (frequency = 2Hz) and the rotor speed oscillates also (frequency = 2Hz). The difference of phase between the 2 oscillations is 180°.

The solution given by the model doesn't converge to the rigth one (see figures below: X-axis = Time [s], Y-axis = Torque [Nm] or Thrust [N] ). I would expect that thrust and torque oscillate with a frequency of 2Hz.

I have tried several settings (DT, number of panels, CircSolvConvCrit, CircSolvRelaxation, CircSolvMaxIter...), but I'm not able to get good results. Do you have any suggestions to solve the problem?

Thank you

AERODYN.dat, Aerodyn_driver.dvr, OLAF.dat are attached below.

*The red line is the mean expect value.

AERODYN.dat

------- AERODYN v15.04.* INPUT FILE ------------------------------------------------
Polimi Wind Turbine Model
======  General Options  ============================================================================
False         Echo               - Echo the input to "<rootname>.AD.ech"?  (flag)
"default"     DTAero             - Time interval for aerodynamic calculations {or "default"} (s)
          3   WakeMod            - Type of wake/induction model (switch) {0=none, 1=BEMT}
          2   AFAeroMod          - Type of blade airfoil aerodynamics model (switch) {1=steady model, 2=Beddoes-Leishman unsteady model} [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)
False         Buoyancy           - Include buoyancy effects? (flag)
False         CompAA             - Flag to compute AeroAcoustics calculation [only used when WakeMod=1 or 2]
"unused"      AA_InputFile       - Aeroacoustics input file
======  Environmental Conditions  ===================================================================
      1.177   AirDens            - Fluiddensity (kg/m^3)
    1.45e-5   KinVisc            - Kinematic viscosity (m^2/s)
        335   SpdSound           - Speed of sound (m/s)
     103500   Patm               - Atmospheric pressure (Pa) [used only when CavitCheck=True]
       1700   Pvap               - Vapour pressure of fluid (Pa) [used only when CavitCheck=True]
======  Blade-Element/Momentum Theory Options  ====================================================== [used only when WakeMod=1]
1             SkewMod            - Type of skewed-wake correction model (switch) {1=uncoupled, 2=Pitt/Peters, 3=coupled} [used only when WakeMod=1]
"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]
True          TipLoss            - Use the Prandtl tip-loss model? (flag) [used only when WakeMod=1]
True          HubLoss            - Use the Prandtl hub-loss model? (flag) [used only when WakeMod=1]
True          TanInd             - Include tangential induction in BEMT calculations? (flag) [used only when WakeMod=1]
True          AIDrag             - Include the drag term in the axial-induction calculation? (flag) [used only when WakeMod=1]
True          TIDrag             - Include the drag term in the tangential-induction calculation? (flag) [used only when WakeMod=1 and TanInd=TRUE]
      5E-05   IndToler           - Convergence tolerance for BEMT nonlinear solve residual equation {or "default"} (-) [used only when WakeMod=1]
      10000   MaxIter            - Maximum number of iteration steps (-) [used only when WakeMod=1]
======  Dynamic Blade-Element/Momentum Theory Options  ====================================================== [used only when WakeMod=1]
2             DBEMT_Mod          - Type of dynamic BEMT (DBEMT) model {1=constant tau1, 2=time-dependent tau1} (-) [used only when WakeMod=2]
2             tau1_const         - Time constant for DBEMT (s) [used only when WakeMod=2 and DBEMT_Mod=1]
======  OLAF -- cOnvecting LAgrangian Filaments (Free Vortex Wake) Theory Options  ================== [used only when WakeMod=3]
"OLAF.dat"      OLAFInputFileName  - Input file for OLAF [used only when WakeMod=3]
======  Beddoes-Leishman Unsteady Airfoil Aerodynamics Options  ===================================== [used only when AFAeroMod=2]
5             UAMod       Unsteady Aero Model Switch (switch) {1=Baseline model (Original), 2=Gonzalez's variant (changes in Cn,Cc,Cm), 3=Minemma/Pierce variant (changes in Cc and Cm)} [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]
0.25          UAStartRad  - Starting radius for dynamic stall (fraction of rotor radius) [used only when AFAeroMod=2]
0.95          UAEndRad    - Ending radius for dynamic stall (fraction of rotor radius) [used only when AFAeroMod=2]
======  Airfoil Information =========================================================================
          2   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 (-)
          39  NumAFfiles         - Number of airfoil files used (-)
"Airfoils_v3/_coarseMod/airfoilEL_1.dat"
"Airfoils_v3/_coarseMod/airfoilEL_2.dat"
"Airfoils_v3/_coarseMod/airfoilEL_3.dat"
"Airfoils_v3/_coarseMod/airfoilEL_4.dat"
"Airfoils_v3/_coarseMod/airfoilEL_5.dat"
"Airfoils_v3/_coarseMod/airfoilEL_6.dat"
"Airfoils_v3/_coarseMod/airfoilEL_7.dat"
"Airfoils_v3/_coarseMod/airfoilEL_8.dat"
"Airfoils_v3/_coarseMod/airfoilEL_9.dat"
"Airfoils_v3/_coarseMod/airfoilEL_10.dat"
"Airfoils_v3/_coarseMod/airfoilEL_11.dat"
"Airfoils_v3/_coarseMod/airfoilEL_12.dat"
"Airfoils_v3/_coarseMod/airfoilEL_13.dat"
"Airfoils_v3/_coarseMod/airfoilEL_14.dat"
"Airfoils_v3/_coarseMod/airfoilEL_15.dat"
"Airfoils_v3/_coarseMod/airfoilEL_16.dat"
"Airfoils_v3/_coarseMod/airfoilEL_17.dat"
"Airfoils_v3/_coarseMod/airfoilEL_18.dat"
"Airfoils_v3/_coarseMod/airfoilEL_19.dat"
"Airfoils_v3/_coarseMod/airfoilEL_20.dat"
"Airfoils_v3/_coarseMod/airfoilEL_21.dat"
"Airfoils_v3/_coarseMod/airfoilEL_22.dat"
"Airfoils_v3/_coarseMod/airfoilEL_23.dat"
"Airfoils_v3/_coarseMod/airfoilEL_24.dat"
"Airfoils_v3/_coarseMod/airfoilEL_25.dat"
"Airfoils_v3/_coarseMod/airfoilEL_26.dat"
"Airfoils_v3/_coarseMod/airfoilEL_27.dat"
"Airfoils_v3/_coarseMod/airfoilEL_28.dat"
"Airfoils_v3/_coarseMod/airfoilEL_29.dat"
"Airfoils_v3/_coarseMod/airfoilEL_30.dat"
"Airfoils_v3/_coarseMod/airfoilEL_31.dat"
"Airfoils_v3/_coarseMod/airfoilEL_32.dat"
"Airfoils_v3/_coarseMod/airfoilEL_33.dat"
"Airfoils_v3/_coarseMod/airfoilEL_34.dat"
"Airfoils_v3/_coarseMod/airfoilEL_35.dat"
"Airfoils_v3/_coarseMod/airfoilEL_36.dat"
"Airfoils_v3/_coarseMod/airfoilEL_37.dat"
"Airfoils_v3/_coarseMod/airfoilEL_38.dat"
"Airfoils_v3/_coarseMod/airfoilEL_39.dat"
======  Rotor/Blade Properties  =====================================================================
False          UseBlCm            - Include aerodynamic pitching moment in calculations?  (flag)
"AERODYN_Blade.dat"                 ADBlFile(1)        - Name of file containing distributed aerodynamic properties for Blade #1 (-)
"AERODYN_Blade.dat"                 ADBlFile(2)        - Name of file containing distributed aerodynamic properties for Blade #2 (-) [unused if NumBl < 2]
"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=True, or TwrAero=True]
         1    NumTwrNds         - Number of tower nodes used in the analysis  (-) [used only when TwrPotent/=0, TwrShadow=True, or TwrAero=True]
TwrElev        TwrDiam        TwrCd          TwrTI			 TwrCb !TwrTI used only with TwrShadow=2, TwrCb used only with Buoyancy=True
(m)              (m)           (-)
1              1.0            1.0            0.1			 0.0
======  Outputs  ====================================================================================
False         SumPrint            - Generate a summary file listing input options and interpolated properties to "<rootname>.AD.sum"?  (flag)
          9   NBlOuts             - Number of blade node outputs [0 - 9] (-)
          1,2,3,4,5,6,7,8,9    BlOutNd             - Blade nodes whose values will be output  (-)
          0   NTwOuts             - Number of tower node outputs [0 - 9]  (-)
          1   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, (-)

"RtAeroMxh, RtAeroFxh, RtFldCp"

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

Aerodyn_driver.dvr

**_----- AeroDyn Driver Input File ---------------------------------------------------------
BAR turbine driver input file, using advanced input, sinusoidal base motion
----- Input Configuration ---------------------------------------------------------------
False           Echo         - Echo input parameters to "<rootname>.ech"?
         0      MHK          - MHK turbine type (switch) {0: not an MHK turbine, 1: fixed MHK turbine, 2: floating MHK turbine}
         1      AnalysisType - {1: multiple turbines, one simulation, 2: one turbine, one time-dependent simulation, 3: one turbine, combined cases}
         6      TMax         - Total run time [used only when AnalysisType/=3] (s)
         0.001  DT           - Simulation time step [used only when AnalysisType/=3] (s)
"./AERODYN.dat" AeroFile     - Name of the primary AeroDyn input file
----- Environmental Conditions ----------------------------------------------------------
     1.177     FldDens      - Density of working fluid (kg/m^3)
   1.45e-5     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]
         0     WtrDpth      - Water depth (m)
----- Inflow Data -----------------------------------------------------------------------
          0      CompInflow  - Compute inflow wind velocities (switch) {0=Steady Wind; 1=InflowWind}
"./InflowWind" InflowFile    - Name of the InflowWind input file [used only when CompInflow=1]
       4.19      HWindSpeed  - Horizontal wind speed   [used only when CompInflow=0 and AnalysisType=1] (m/s)
        1.2      RefHt       - Reference height for horizontal wind speed [used only when CompInflow=0]     (m)
          0      PLExp       - Power law exponent   [used only when CompInflow=0 and AnalysisType=1]                           (-)
----- Turbine Data ----------------------------------------------------------------------
1               NumTurbines - Number of turbines
----- Turbine(1) ------------------------------------------------------------------------
False                     BasicHAWTFormat(1)     - Flag to switch between basic or generic input format {True: next 7 lines are basic inputs, False: Base/Twr/Nac/Hub/Bld geometry and motion must follow}
0,0,0.45                  BaseOriginInit(1)      - x,y,z coordinates of base origin (m)
0,0,0                     BaseOrientationInit(1) - successive rotations (theta_x, theta_y, theta_z) defining initial orientation of the base frame from the global frame (e.g. roll, tilt, yaw) (deg)
True                      HasTower(1)            - True if turbine has a tower (flag)
True                      HAWTprojection(1)      - True if turbine is a horizontal axis turbine (for AeroDyn projections) (flag)
0,0,0                     TwrOrigin_t(1)         - Coordinate of tower base in base coordinates [used only when HasTower is True] (m)
-0.139946,0,1.599590      NacOrigin_t(1)         - x,y,z coordinates of nacelle origin (and tower top) from base, in base coordinates (m)
-0.091114,0,0.044781      HubOrigin_n(1)         - NOTE: Bar has 7m overhang, tilt of 6deg, and twr2shaft 3.09343 x,y,z coordinates of hub origin from nacelle origin, in nacelle coordinates (m)
0,0,0                     HubOrientation_n(1)    - successive rotations (theta_x, theta_y, theta_z) defining initial orientation of the hub frame from the nacelle frame (e.g. roll, tilt, yaw). The x axis needs to be aligned with the rotational speed. (deg)
----- Turbine(1) Blades -----------------------------------------------------------------
3               NumBlades(1)          - Number of blades for current rotor (-)
0,0,0           BldOrigin_h(1_1)      - Orign of blade 1 wrt. hub origin in hub coordinates (m)
0,0,0           BldOrigin_h(1_2)      - Orign of blade 2 wrt. hub origin in hub coordinates (m)
0,0,0           BldOrigin_h(1_3)      - Orign of blade 3 wrt. hub origin in hub coordinates (m)
0,0,0           BldOrientation_h(1_1) - successive rotations (theta_x, theta_y, theta_z) defining initial orientation of the blade frame from the hub frame such that the "z" is along span, "y" along trailing edge without pitch (azimuth, precone, pitch) (deg)
120,0,0         BldOrientation_h(1_2) - successive rotations (theta_x, theta_y, theta_z) defining initial orientation of the blade frame from the hub frame such that the "z" is along span, "y" along trailing edge without pitch (azimuth, precone, pitch) (deg)
240,0,0         BldOrientation_h(1_3) - successive rotations (theta_x, theta_y, theta_z) defining initial orientation of the blade frame from the hub frame such that the "z" is along span, "y" along trailing edge without pitch (azimuth, precone, pitch) (deg)
0.089           BldHubRad_bl(1_1)     - z-offset in blade coordinates of blade 1 where radial input data start (m)
0.089           BldHubRad_bl(1_2)     - z-offset in blade coordinates of blade 2 where radial input data start (m)
0.089           BldHubRad_bl(1_3)     - z-offset in blade coordinates of blade 3 where radial input data start (m)
----- Turbine(1) Motion [used only when AnalysisType=1] ---------------------------------
1               BaseMotionType(1)       - Type of motion prescribed for this base {0: fixed, 1: Sinusoidal motion, 2: arbitrary motion} (flag)
1               DegreeOfFreedom(1)      - {1:xt, 2:yt, 3:zt, 4:theta_xt, 5:theta_yt, 6:theta_zt} [used only when BaseMotionType=1] (flag)
0.08            Amplitude(1)            - Amplitude of sinusoidal motion   [used only when BaseMotionType=1] (m or rad)
2               Frequency(1)            - Frequency of sinusoidal motion   [used only when BaseMotionType=1] (Hz)
"unused"        BaseMotionFileName(1)   - Filename containing arbitrary base motion (19 columns: Time, x, y, z, theta_x, ..., alpha_z)  [used only when BaseMotionType=2]
0               NacMotionType(1)        - Type of motion prescribed for the nacelle {0: fixed yaw, 1: time varying yaw angle} (flag)
0               NacYaw(1)               - Yaw angle (about z_t) of the nacelle [user only when NacMotionType=0] (deg)
"unused"        NacMotionFileName(1)    - Filename containing yaw motion [used only when NacMotionType=1]
1               RotMotionType(1)        - Type of motion prescribed for this rotor {0: constant rotation, 1: time varying rotation} (flag)
240             RotSpeed(1)             - Rotational speed of rotor in rotor coordinates [used only when RotorMotionType=0] (rpm)
"RotMotionFile"        RotMotionFileName(1)    - Filename containing rotor motion [used only when RotorMotionType=1]
0               BldMotionType(1)        - Type of pitch motion prescribed for the blades {0: fixed, 1: time varying pitch} (flag)
0               BldPitch(1_1)           - Blade 1 pitch [used only when BldMotionType=0] (deg)
0               BldPitch(1_2)           - Blade 2 pitch [used only when BldMotionType=0] (deg)
0               BldPitch(1_3)           - Blade 3 pitch [used only when BldMotionType=0] (deg)
"unused" BldMotionFileName(1_1)  - Filename containing blade pitch motion [used only when BldMotionType=1]
"unused" BldMotionFileName(1_2)  - Filename containing blade pitch motion [used only when BldMotionType=1]
"unused" BldMotionFileName(1_3)  - Filename containing blade pitch motion [used only when BldMotionType=1]
----- Time-dependent Analysis [used only when AnalysisType=2, numTurbines=1] ------------
"unused"         TimeAnalysisFileName - Filename containing time series (6 column: Time, HWndSpeed, PLExp, RotSpd, Pitch, Yaw). 
----- Combined-Case Analysis [used only when AnalysisType=3, numTurbines=1] -------------
          0  NumCases     - Number of cases to run
HWndSpeed    PLExp        RotSpd       Pitch        Yaw     dT      Tmax  DOF  Amplitude Frequency 
(m/s)        (-)          (rpm)        (deg)        (deg)   (s)     (s)    (-)  (m or rad) (Hz)
----- Output Settings -------------------------------------------------------------------
"ES15.8E2"  OutFmt        - Format used for text tabular output, excluding the time channel.  Resulting field should be 10 characters. (quoted string)
1           OutFileFmt    - Format for tabular (time-marching) output file (switch) {1: text file [<RootName>.out], 2: binary file [<RootName>.outb], 3: both}
0           WrVTK         - VTK visualization data output: (switch) {0=none; 1=init; 2=animation}
2           WrVTK_Type    - VTK visualization data type: (switch) {1=surfaces; 2=lines; 3=both}
2           VTKHubRad     - HubRadius for VTK visualization (m)
-7,-4,0,21,8,8    VTKNacDim     - Nacelle Dimension for VTK visualization x0,y0,z0,Lx,Ly,Lz (m)_**

OLAF.dat

--------------------------- OLAF (cOnvecting LAgrangian Filaments) INPUT FILE -----------------
Free wake input file for the Helix test case
--------------------------- GENERAL OPTIONS ---------------------------------------------------
default IntMethod          - Integration method {1: RK4, 5: Forward Euler 1st order, default: 5} (switch) 
default DTfvw              - Time interval for wake propagation. {default: dtaero} (s)
default FreeWakeStart      - Time when wake is free. (-) value = always free. {default: 0.0} (s)
default FullCircStart      - Time at which full circulation is reached. {default: 0.0} (s)
--------------------------- CIRCULATION SPECIFICATIONS ----------------------------------------
default CircSolvMethod     - Circulation solving method {1: Cl-Based, 2: No-Flow Through, 3: Prescribed, default: 1 }(switch)
0.0001  CircSolvConvCrit   - Convergence criteria {default: 0.001} [only if CircSolvMethod=1] (-)
0.01    CircSolvRelaxation - Relaxation factor {default: 0.1} [only if CircSolvMethod=1] (-)
40      CircSolvMaxIter    - Maximum number of iterations for circulation solving {default: 30} (-)
"./Helix_PrescribedGamma.csv"  - PrescribedCircFile File containing prescribed circulation [only if CircSolvMethod=3] (quoted string)
===============================================================================================
--------------------------- WAKE OPTIONS ------------------------------------------------------
------------------- WAKE EXTENT AND DISCRETIZATION --------------------------------------------
1000    nNWPanels          - Number of near-wake panels (-)
1000    nNWPanelsFree      - Number of free near-wake panels (-) {default: nNWPanels}
1274    nFWPanels          - Number of far-wake panels (-) {default: 0}
1000    nFWPanelsFree      - Number of free far-wake panels (-) {default: nFWPanels}
True    FWShedVorticity    - Include shed vorticity in the far wake {default: False}
------------------- WAKE REGULARIZATIONS AND DIFFUSION -----------------------------------------
0       DiffusionMethod    - Diffusion method to account for viscous effects {0: None, 1: Core Spreading, "default": 0}         
3       RegDeterMethod     - Method to determine the regularization parameters {0:  Manual, 1: Optimized, 2: Chord, 3: Span, default: 0 }          
3       RegFunction        - Viscous diffusion function {0: None, 1: Rankine, 2: LambOseen, 3: Vatistas, 4: Denominator, "default": 3} (switch)
3       WakeRegMethod      - Wake regularization method {1: Constant, 2: Stretching, 3: Age, default: 3} (switch)
0.6     WakeRegFactor      - Wake regularization factor (m or -)
0.6     WingRegFactor      - Wing regularization factor (m or -)
1000     CoreSpreadEddyVisc - Eddy viscosity in core spreading methods, typical values 1-1000 
------------------- WAKE TREATMENT OPTIONS ---------------------------------------------------
default TwrShadowOnWake    - Include tower flow disturbance effects on wake convection {default:false} [only if TwrPotent or TwrShadow]
default ShearModel         - Shear Model {0: No treatment, 1: Mirrored vorticity, default: 0}
------------------- SPEEDUP OPTIONS -----------------------------------------------------------
default VelocityMethod     - Method to determine the velocity {1:Segment N^2, 2:Particle tree, 3:Particle N^2, 4:Segment tree, default: 2}
default TreeBranchFactor   - Branch radius fraction above which a multipole calculation is used {default: 1.5} [only if VelocityMethod=2,4]
default PartPerSegment     - Number of particles per segment {default: 1} [only if VelocityMethod=2,3]
===============================================================================================
--------------------------- OUTPUT OPTIONS  ---------------------------------------------------
0       WrVTk              - Outputs Visualization Toolkit (VTK) (independent of .fst option) {0: NoVTK, 1: Write VTK at VTK_fps, 2: Write VTK at init and final, default: 0} (flag)
default nVTKBlades         - Number of blades for which VTK files are exported {0: No VTK per blade, n: VTK for blade 1 to n, default: 0} (-) 
default VTKCoord           - Coordinate system used for VTK export. {1: Global, 2: Hub, 3: Both, default: 1} 
default VTK_fps            - Frame rate for VTK output (frames per second) {"all" for all glue code timesteps, "default" for all OLAF timesteps} [only if WrVTK=1] 
0       nGridOut           - Number of grid outputs
GridName  GridType  TStart   TEnd    DTGrid   XStart  XEnd   nX   YStart   YEnd   nY   ZStart   ZEnd   nZ
(-)         (-)      (s)     (s)      (s)       (m)    (m)   (-)   (m)     (m)    (-)   (m)     (m)    (-)
===============================================================================================
--------------------------- ADVANCED OPTIONS --------------------------------------------------
===============================================================================================

[jjonkman]

Dear @Laurens09,

Ignoring the details of your simulation set-up at first (which I haven't reviewed yet), it doesn't appear that your solution has converged and reached a periodic steady state yet. You appear to be showing only results over the first 1.5 seconds of a longer simulation. Does the solution reach a periodic steady state if you run the simulation for longer?

Best regards,

[Laurens09]

No, I have run simulations up to 2/3s (in some cases more), but covergence is not reached anyway. Is there a reasonable time after which I should expect convergence?

[RBergua]

Dear @Laurens09,

The load case that you are running seems to be the Load Case 2.16 from OC6 phase III (https://wes.copernicus.org/articles/8/465/2023/wes-8-465-2023-discussion.html). I think the only difference is that you are running with the original UNAFLOW definition of 39 aerodynamic sections instead of the simplified 20 sections that we used in the OC6 phase III project.

Below you can see the response in time domain that we obtained when using OLAF:

Somehow, your plots are very noisy. This is not expected for a spatially uniform wind inflow. By the way, I believe both plots that you shared correspond to aerodynamic torque.

I suspect the RotMotionFile could be wrong. Note that you should provide 4 columns with:

1. Time [s]
2. Azimuth [rad]
3. Angular velocity [rad/s]
4. Angular acceleration [rad/s^2]

And the azimuth must be an unwrapped angle. See below for reference:

I would probably recommend starting without platform motion nor rotor speed variations and check the outputs against Figures 3 and 4 from the OC6 phase III paper commented above.

I hope that helps!