Modelling Parked (Standstill) condition for VolturnUS-S Floating Wind Turbine

Hi everyone:

I am trying to model the parked/standstill condition in openfast using VolturnUS-S semisubmersible. I have set GenDOF = False, feathered blades to 90 degrees and set initial rotor speed to zero in ElastoDyn. PCMode=0 in ServoDyn.

In AeroDyn, I have set WakeMoD=0 and AFAeroMod=1.0.

However, I get this error:

FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption

violated in SUBROUTINE SmllRotTrans() due to a large blade deflection (ElastoDyn SetCoordSy). The

solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will

be suppressed.

Additional debugging message from SUBROUTINE SmllRotTrans(): 0.725 s

FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalcOutput:IfW_FF

Wind_CalcOutput [position=(5.5972, -4.9906, 1.863) in wind-file coordinates]: FF wind array

boundaries violated. Grid too small in Z direction (height (Z=1.863 m) is below the grid and no

tower points are defined).

OpenFAST encountered an error at simulation time 0.95 of 3600 seconds.

Simulation error level: FATAL ERROR

In the z-direction my grid goes from 2.5 to 297.5 m that is grid height is 295 m. This is the limit based on grid height criteria in TurbSim.

Do you know how I could fix this problem?

Regards,
AOAW

Hi @Jason.Jonkman:
I have moved the discussion on modelling parked (standstill) turbine to the following forum.

You responded as follows in the Tower Strike with latest version of OpenFAST forum:
“It sounds like your model has gone unstable. Can you clarify your simulation settings? It sounds like you’ve parked the rotor with GenDOF = False and RotSpeed = 0.0 rpm and have set the pitch angles to BlPitch = 91.5deg. Can you confirm? Are you getting these errors only for certain yaw misalignments (wind directions)?”

I have only considered one case, the 0 degree wind direction. The relevant settings of ElastoDyn and ServoDyn are shown below:

------- ELASTODYN v1.03. INPUT FILE -------------------------------------------*
IEA 15 MW offshore reference model on UMaine VolturnUS-S semi-submersible floating platform
---------------------- SIMULATION CONTROL --------------------------------------
False Echo - Echo input data to “.ech” (flag)
** 3 Method - Integration method: {1: RK4, 2: AB4, or 3: ABM4} (-)**
“default” DT Integration time step (s)
---------------------- DEGREES OF FREEDOM --------------------------------------
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]
False DrTrDOF - Drivetrain rotational-flexibility DOF (flag)
False GenDOF - Generator DOF (flag)
False YawDOF - Yaw DOF (flag)
True TwFADOF1 - First fore-aft tower bending-mode DOF (flag)
True TwFADOF2 - Second fore-aft tower bending-mode DOF (flag)
True TwSSDOF1 - First side-to-side tower bending-mode DOF (flag)
True TwSSDOF2 - Second side-to-side tower bending-mode DOF (flag)
True PtfmSgDOF - Platform horizontal surge translation DOF (flag)
True PtfmSwDOF - Platform horizontal sway translation DOF (flag)
True PtfmHvDOF - Platform vertical heave translation DOF (flag)
True PtfmRDOF - Platform roll tilt rotation DOF (flag)
True PtfmPDOF - Platform pitch tilt rotation DOF (flag)
True PtfmYDOF - Platform yaw rotation DOF (flag)
---------------------- INITIAL CONDITIONS --------------------------------------
0 OoPDefl - Initial out-of-plane blade-tip displacement (meters)
0 IPDefl - Initial in-plane blade-tip deflection (meters)
91.5 BlPitch(1) - Blade 1 initial pitch (degrees)
91.5 BlPitch(2) - Blade 2 initial pitch (degrees)
** 91.5 BlPitch(3) - Blade 3 initial pitch (degrees) [unused for 2 blades]**
** 0 TeetDefl - Initial or fixed teeter angle (degrees) [unused for 3 blades]**
** 0 Azimuth - Initial azimuth angle for blade 1 (degrees)**
0.00 RotSpeed - Initial or fixed rotor speed (rpm)
0 NacYaw - Initial or fixed nacelle-yaw angle (degrees)
** 0 TTDspFA - Initial fore-aft tower-top displacement (meters)**
** 0 TTDspSS - Initial side-to-side tower-top displacement (meters)**
** 0 PtfmSurge - Initial or fixed horizontal surge translational displacement of platform (meters)**
** 0 PtfmSway - Initial or fixed horizontal sway translational displacement of platform (meters)**
** 0 PtfmHeave - Initial or fixed vertical heave translational displacement of platform (meters)**
** 0 PtfmRoll - Initial or fixed roll tilt rotational displacement of platform (degrees)**
** 0 PtfmPitch - Initial or fixed pitch tilt rotational displacement of platform (degrees)**
** 0 PtfmYaw - Initial or fixed yaw rotational displacement of platform (degrees)**

The value I used for BldEdDmp1 is shown below:
4.5 BldEdDmp1 - Blade edge mode #1 structural damping in percent of critical (%)

------- SERVODYN v1.05.* INPUT FILE --------------------------------------------
IEA 15 MW offshore reference model on UMaine VolturnUS-S semi-submersible floating platform
---------------------- SIMULATION CONTROL --------------------------------------
False Echo - Echo input data to .ech (flag)
“default” DT - Communication interval for controllers (s) (or “default”)
---------------------- PITCH CONTROL -------------------------------------------
0 PCMode - Pitch control mode {0: none, 3: user-defined from routine PitchCntrl, 4: user-defined from Simulink/Labview, 5: user-defined from Bladed-style DLL} (switch)
0.0 TPCOn - Time to enable active pitch control (s) [unused when PCMode=0]
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]
2.0 PitManRat(1) - Pitch rate at which override pitch maneuver heads toward final pitch angle for blade 1 (deg/s)
2.0 PitManRat(2) - Pitch rate at which override pitch maneuver heads toward final pitch angle for blade 2 (deg/s)
2.0 PitManRat(3) - Pitch rate at which override pitch maneuver heads toward final pitch angle for blade 3 (deg/s) [unused for 2 blades]
0.0 BlPitchF(1) - Blade 1 final pitch for pitch maneuvers (degrees)
0.0 BlPitchF(2) - Blade 2 final pitch for pitch maneuvers (degrees)
0.0 BlPitchF(3) - Blade 3 final pitch for pitch maneuvers (degrees) [unused for 2 blades]
---------------------- GENERATOR AND TORQUE CONTROL ----------------------------
0 VSContrl - Variable-speed control mode {0: none, 1: simple VS, 3: user-defined from routine UserVSCont, 4: user-defined from Simulink/Labview, 5: user-defined from Bladed-style DLL} (switch)
1 GenModel - Generator model {1: simple, 2: Thevenin, 3: user-defined from routine UserGen} (switch) [used only when VSContrl=0]
95.756 GenEff - Generator efficiency [ignored by the Thevenin and user-defined generator models] (%)
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]
---------------------- SIMPLE VARIABLE-SPEED TORQUE CONTROL --------------------
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]
---------------------- 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]
100 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]
---------------------- HIGH-SPEED SHAFT BRAKE ----------------------------------
0 HSSBrMode - HSS brake model {0: none, 1: simple, 3: user-defined from routine UserHSSBr, 4: user-defined from Simulink/Labview, 5: user-defined from Bladed-style DLL} (switch)
0 THSSBrDp - Time to initiate deployment of the HSS brake (s)
0 HSSBrDT - Time for HSS-brake to reach full deployment once initiated (sec) [used only when HSSBrMode=1]
9999.9 HSSBrTqF - Fully deployed HSS-brake torque (N-m)
---------------------- NACELLE-YAW CONTROL -------------------------------------
0 YCMode - Yaw control mode {0: none, 3: user-defined from routine UserYawCont, 4: user-defined from Simulink/Labview, 5: user-defined from Bladed-style DLL} (switch)
9999.9 TYCOn - Time to enable active yaw control (s) [unused when YCMode=0]
0.0 YawNeut - Neutral yaw position–yaw spring force is zero at this yaw (degrees)
8458453511.0 YawSpr - Nacelle-yaw spring constant (N-m/rad)
28561762.0 YawDamp - Nacelle-yaw damping constant (N-m/(rad/s))
9999.9 TYawManS - Time to start override yaw maneuver and end standard yaw control (s)
0.25 YawManRat - Yaw maneuver rate (in absolute value) (deg/s)
0.0 NacYawF - Final yaw angle for override yaw maneuvers (degrees)
---------------------- Aerodynamic Flow Control -------------------------------------
0 AfCmode - Airfoil control mode {0- none, 1- cosine wave cycle, 4- user-defined from Simulink/Labview, 5- user-defined from Bladed-style DLL}
0.0 AfC_Mean - Mean level for sinusoidal cycling or steady value (-) [used only with AfCmode==1]
0.0 AfC_Amp - Amplitude for for cosine cycling of flap signal (AfC = AfC_Amp*cos(Azimuth+phase)+AfC_mean) (-) [used only with AfCmode==1]
0.0 AfC_phase - Phase relative to the blade azimuth (0 is vertical) for for cosine cycling of flap signal (deg) [used only with AfCmode==1]

The error that I get with those settings is shown below:
FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption
violated in SUBROUTINE SmllRotTrans() due to a large blade deflection (ElastoDyn SetCoordSy). The
solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will
be suppressed.
** Additional debugging message from SUBROUTINE SmllRotTrans(): 0.725 s**

FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalcOutput:IfW_FF
Wind_CalcOutput [position=(-16.053, -42.159, 314.03) in wind-file coordinates]: FF wind array
boundaries violated. Grid too small in Z direction (Z=314.03 m is above the grid).OpenFAST encountered an error at simulation time 1.025 of 3600 seconds. Simulation error level: FATAL ERROR

As you have pointed out the model has gone unstable. Please Let me know how I could fix it. I have tried changing the blade structural damping value mention above but that did not help.

Regards,
AOAW

Dear @Andre.White,

Have you changed other settings in the OpenFAST model, e.g., HydroDyn or MooDyn?

Can you clarify what solver settings you’ve set in the OpenFAST primary (**.fst*) input file, i.e., DT, NumCrctn, DT_UJac, and UJacSclFact? Does dropping DT have any impact on the solution?

What do the blade, tower, and platform deflections/displacements look like during the 1-s simulation?

Best regards,

Hi @Jason.Jonkman I have changed the water depth from 200 m to 100 m and modified the mooring line dimensions for water depth of 100 m. I have set up the system such that the system has a mean heave of zero in the still water condition. These are my settings in MoorDyn.

**--------------------- MoorDyn Input File ------------------------------------ **
**IEA 15 MW offshore reference model on UMaine VolturnUS-S semi-submersible floating platform mooring model- C. Allen UMaine **
**FALSE Echo - echo the input file data (flag) **
**----------------------- LINE TYPES ------------------------------------------ **
**1 NTypes - number of LineTypes **
**Name Diam MassDen EA BA/-zeta Can Cat Cdn Cdt **
**(-) (m) (kg/m) (N) (N-s/-) (-) (-) (-) (-) **
**main 0.30 1971.00 8.1E+09 -1 0.82 0.27 1.11 0.20 **
**---------------------- CONNECTION PROPERTIES -------------------------------- **
**6 NConnects - number of connections including anchors and fairleads **
Node Type X Y Z M V FX FY FZ CdA CA
(-) (-) (m) (m) (m) (kg) (m^3) (kN) (kN) (kN) (m^2) (-)
1 Vessel -58.000 0.000 -14.000 0 0 0 0 0 0 0
2 Fixed -418.500 0.000 -100.000 0 0 0 0 0 0 0
3 Vessel 29.000 50.229 -14.000 0 0 0 0 0 0 0
4 Fixed 209.250 362.432 -100.000 0 0 0 0 0 0 0
5 Vessel 29.000 -50.229 -14.000 0 0 0 0 0 0 0
6 Fixed 209.250 -362.432 -100.000 0 0 0 0 0 0 0
**---------------------- LINE PROPERTIES -------------------------------------- **
**3 NLines - number of line objects **
Line LineType UnstrLen NumSegs NodeAnch NodeFair Outputs CtrlChan
(-) (-) (m) (-) (-) (-) (-) (-)
1 main 415.00 50 2 1 pt 0
2 main 415.00 50 4 3 pt 0
3 main 415.00 50 6 5 pt 0
**---------------------- SOLVER OPTIONS --------------------------------------- **
0.001 dtM - time step to use in mooring integration (s)
3.0e6 kbot - bottom stiffness (Pa/m)
3.0e5 cbot - bottom damping (Pa-s/m)
1.0 dtIC - time interval for analyzing convergence during IC gen (s)
60.0 TmaxIC - max time for ic gen (s)
4.0 CdScaleIC - factor by which to scale drag coefficients during dynamic relaxation (-)
**0.001 threshIC - threshold for IC convergence (-) **
**------------------------ OUTPUTS -------------------------------------------- **
**FairTen1 **
**FairTen2 **
**FairTen3 **
**AnchTen1 **
**AnchTen2 **
**AnchTen3 **
END

These are my simulation control settings. I am not sure what you mean by drop DT as I thought DT was time step for the simulations.
---------------------- SIMULATION CONTROL -------------------------------------- **
** False Echo - Echo input data to .ech (flag) **
** FATAL AbortLevel - Error level when simulation should abort (string) {“WARNING”, “SEVERE”, “FATAL”} **
** 3600 TMax - Total run time (s) **
** 0.025 DT - Integration time step (s) **
** 2 InterpOrder - Interpolation order for input/output time history (-) {1=linear, 2=quadratic} **
** 0 NumCrctn - Number of correction iterations (-) {0=explicit calculation, i.e., no corrections} **
** 99999.0 DT_UJac - Time between calls to get Jacobians (s) **
** 1000000.0 UJacSclFact - Scaling factor used in Jacobians (-)

What do the blade, tower, and platform deflections/displacements look like during the 1-s simulation? Does this mean that simulation time is set to 1s or should I observe what they look like after 1s.

Regards,
AOAW

Hi @Andre.White,

By

dropping DT

, I meant does reducing DT change the solution in any way? If so, this would imply that the solution is not numerically converged, and the instability may be numerical in nature. Otherwise, I would expect a physical instability.

When I asked

what do the blade, tower, and platform deflections/displacements look like during the 1-s simulation

, I was asking what the time series look like during the 1 s you are simulating? Presumably the blade-top deflection time series is increasing exponentially without bound; is that correct? What about the tower deflection and platform displacement time series? I’m trying to understand what in the model is going unstable.

During the simulation that goes unstable, what wave conditions are used? Is the OpenFAST model stable at other conditions, e.g. a lower wind speed or less severe sea state?

Best regards,

@Jason.Jonkman thanks for the clarification. I will have to troubleshoot beginning with the value of DT.
The model runs properly when the conditions are normal. So far I was investigating between 9 and 15 m/s wind and the related sea states and the model performs well. The model breaks down for the extreme wind and sea state. However, I see where others have run simulations for extreme conditions so I believe there is a way to do it. I just have not figured it out just yet.

Regards,
AOAW

Hi @Jason.Jonkman:

I changed value of DT to make it smaller but the model is still unstable. I am still getting the following error.
FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_CalcContStateDeriv:SetCoordSy:Small angle assumption

violated in SUBROUTINE SmllRotTrans() due to a large blade deflection (ElastoDyn SetCoordSy). The

solution may be inaccurate. Simulation continuing, but future warnings from SmllRotTrans() will

be suppressed.

Additional debugging message from SUBROUTINE SmllRotTrans(): 0.725 s

FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalcOutput:IfW_FF

Wind_CalcOutput [position=(-16.053, -42.159, 314.03) in wind-file coordinates]: FF wind array

boundaries violated. Grid too small in Z direction (Z=314.03 m is above the grid).

OpenFAST encountered an error at simulation time 1.025 of 3600 seconds.

Simulation error level: FATAL ERROR

Also note the following:

  1. The parked/idle case runs fine. The only change I made was to set GenDOF=True and model runs with no problem
  2. The original case for 200 m deep water also gives error when I try to run the parked/standstill case
  3. For lower wind speed that is 9 m/s the model still gives error for the parked/standstill case.
    Not sure how to solve this problem as yet.

Problem No. 2 - I also have another problem. It has persisted for some time but only now bringing it to your attention. I have tried to a wind only case for 11 m/s turbulent wind and get the following error:
FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:RotCalcOutput:BEMT_CalcOutput(node 3,

blade 1):UA_CalcOutput:UA_BlendSteady:Temporarily turning off UA due to high angle of attack or

low relative velocity. This warning will not be repeated though the condition may persist.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:RotCalcOutput:BEMT_CalcOutput(node 50,

blade 1):UA_CalcOutput:Mach number exceeds 0.3. Theory is invalid. This warning will not be

repeated though the condition may persist.

Warning: SkewedWakeCorrection encountered a large value of chi (90.407 deg), so the yaw

correction will be limited. This warning will not be repeated though the condition may persist.

See the AD15 chi output channels, and consider turning off the Pitt/Peters skew model (set

SkewMod=1) if this condition persists.

FAST_Solution:FAST_AdvanceStates:SolveOption2c_Inp2AD_SrvD:InflowWind_CalcOutput:CalcOutput:IfW_FF

Wind_CalcOutput [position=(0.13124, -1.42073E-03, 2.421) in wind-file coordinates]: FF wind

array boundaries violated. Grid too small in Z direction (height (Z=2.421 m) is below the grid

and no tower points are defined).

OpenFAST encountered an error at simulation time 1.575 of 3600 seconds.

Simulation error level: FATAL ERROR
I am not sure why this is so. I have turned off HydroDyn and MoorDyn for wind only case. When I ran the wind and wave case the model worked fine, so not sure.
Let me know if you have any ideas about problem 1 and this new problem, problem no. 2.

Thank you.

Regards,
AOAW

Dear @Andre.White,

Regarding the parked case, this is quite surprising. In the idling case, presumably the rotor is rotating a bit? This could mean that the instability is azimuth dependent. That is, the idling case never dwells in the instability; also, it may be possible to park the rotor at an azimuth angle that is stable.

Can you clarify what wind conditions you are simulating? Are you using full-field turbulence or is wind steady and uniform?

I’m also still interested to see the time series of blade deflection, tower deflection, and platform displacement for the short time the simulation runs as I mentioned before.

Regarding problem 2, you mentioned that you disabled HydroDyn and MoorDyn. Does that mean that you’ve disabled the platform DOFs in ElastoDyn? If not, the turbine would fall due to gravity and cause all sorts of errors.

Best regards,

Hi @Jason.Jonkman:
I will check the azimuth angle. Note the following in response to your queries:

  • The wind condition is full-field turbulence.
  • I am not getting any values in the .out file for that short simulation time.
  • Is there another way to model the wind only case without disabling HydroDyn and MoorDyn? When I disable the DOFs for the platform and increase the damping on the blades (BldFlDmp1, BldFlDmp2, BldEdDmp1) to 45%, the model runs. However, turning off the DOFs essentially result in 0 movement of the platform, so this does not seem to be accurate. I would like to compare wave only, wind only and wave and wind.

Thank you.

Regards,
AOAW

Dear @Andre.White,

Does the parked simulation also go unstable when using steady, uniform wind rather than full-field turbulence?

To ensure that you get output over a short 1-s or so simulation, set TStart = 0 s and DT_Out = “DEFAULT” in the OpenFAST primary (*.fst) input file.

Regarding modeling wind only, it sounds like what you really want is still water as the incident wave, which you can get by keeping HydroDyn and MoorDyn enabled and by setting WaveMod = 0 in HydroDyn.

Best regards,

Hi @Jason.Jonkman:
These are the deflections for blade, tower top and platform displacements (surge, heave, pitch).



image
image
image

The blade deflections seem relatively high.

Regards,
AOAW

Dear @Andre.White,

Indeed it looks like a blade-edgewise instability. I was first expecting a physic instability, but given the every other time step oscillation when the model first goes unstable, I’m now wondering if it is a numerical instability. What does these time series look like if you drop DT by an order of magnitude–from 0.025 to 0.0025 s?

Does the model remain stable if you disable the blade-edgewise DOF (EdgeDOF = False)?

Again, does the parked simulation also go unstable when using steady, uniform wind rather than full-field turbulence?

Best regards,

Hi @Jason.Jonkman:
I have made good progress. I downloaded the latest version of the openfast models and restarted the process. So I have done the following for the original 200 m deep model and my 100 m deep model for 45 m/s steady and turbulent winds:

  1. Wind only case, by setting WaveMod=0, still water.
  2. Parked/idle turbine
  3. Parked /standstill turbine
    The wind only case was also for parked turbine. I have not checked the results as yet though. I also did not have to change the blade structural damping for any of those cases. I believe that takes care of that. I may now have to run the full set of simulations I had done before. I will let you know if I have any problems.

I have another query. I am now doing the parked case with yaw misalignment. I did the following:

  1. Turned on the yaw DOF in ElastoDyn
  2. Set the YCMode in ServoDyn to 5
    I used a yaw misalignment of 30 degrees for the first case. I was getting an error due to large blade deflection and so I set the blade structural damping to 60% and the model stabilizes and runs fine. I will have to see if it holds for other degrees of yaw misalignment.

I would like to know if my set up for yaw misalignment is correct?

I have some queries about TurbSim but I will reserve them for another time. However, making you aware. Maybe about next week I will get around to raising them.

Thank you.

Regards,
AOAW

Dear @Andre.White,

Are you saying that your parked model is now stable? What did you do to fix the issue?

Regarding yaw misalignment, setting YCMode = 5 would only be useful if your DISCON controller supports yaw control; does it? To set a fixed yaw misalignment, you can also keep YawDOF disabled in ElastoDyn and set the initial yaw angle (ElastoDyn input NacYaw) to a nonzero value. Alternatively, you could keep the nacelle-yaw unchanged and change the wind propogation direction (InflowWind input PropagationDir).

Best regards,

Hi @Jason.Jonkman:
I believe the problem I was having was with the initial turbine model that I downloaded from GitHub. I had mixed some of the previous input files from the old version of openfast with the latest version and that seemed to have caused some conflicts. I therefore downloaded the latest version again and ran the simulations from scratch for parked turbine and it worked fine.

I believe the controller supports yaw control. However, I have used the approach to set YawDOF to zero and changed NacYaw. For Nacelle yaw though because of the large blade deflection I had to set the blade structural damping value to 60% (I just picked this value, I will test to see if lower value could work. Nonetheless an appropriately large value has to be selected) for the simulations to run.

Thank you.

Regards,
AOAW

Dear @Andre.White,

OK, thanks for clarifying. I’m glad your parked modeling issue is solved.

Regarding the large blade deflection at high yaw misalignments in the parked or idling condition, sounds like the problem we’ve seen before for other wind turbines, as discussed in the following forum topic: Designing for yaw errors using FAST. Indeed, increasing the blade structural damping is a common solution.

Best regards,

Thanks @Jason.Jonkman .
I have some queries about TurbSim which I am going to send in another forum.

Regards,
AOAW