# Model verification

Dear Dr. Jonkman,

I modeled the wind turbine in region 3 but I got different results in comparison to the FAST. For instance, when I apply a nominal pitch angle to the wind turbine, say 19.94, which its equivalent wind speed is 22m/s; accordingly, I got the rated value of 1.267rpm for the rotor speed in my model. However, when I applied those values in FAST there are fluctuations in the rotor speed, and power coefficient! (Note that I applied the rated value for the generator torque and power in region 3).
For example the rotor speed in FAST in comparison with my model is this:

And the power coefficient, which is my main objective for comparison is this:

Why does the FAST has fluctuations while I only applied nominal values?!

Thanks

Best regards,
Sina

Dear Sina,

You haven’t said anything about your model set up or how FAST’s capabilities compare with those of your model. Regardless, structural degrees of freedom, nonideal initial conditions, gravity, and aerodynamic loading could cause oscillations in the FAST solution.

Best regards,

Dear Dr. Jonkman,

Thanks for your prompt response. My model is very simple. I just modeled the rotor speed dynamics which is a first order differential equation using the aerodynamics torque and generator torque. I only used the initial condition for rotor speed in both models. This is the only initial condition in my model. The aerodynamic loading is calculated by the aerodynamic torque equation in my model. I only applied step and constant inputs to the fast but there is still oscillations. What other set ups I should do in the FAST to eliminate those oscillations?

Thanks,
Best regards,
Sina

Dear Sina,

To reduce the oscillations in FAST, you could disable all structural degrees of freedom, set gravity to zero, ensure that there is no shaft tilt or yaw error, and ensure that the wind inflow is steady and uniform.

Best regards,

Dear Dr. Jonkman,

Thanks again for your prompt response. I set the shaft tilt to zero but when I want to set the gravity to zero Matlab gives me the following error:

Thanks
Best regards,
Sina

Dear Sina,

The error is hopefully self-explanatory. Close the *.HD.sum file you have open before running FAST.

That said, you won’t be able to enable HydroDyn if gravity is zero. I would disable HydroDyn in this case.

Best regards,

Dear Dr. Jonkman,
Thanks for your help. Actually, there was not such file to be opened. How can I disable the HydroDyn?

Anyway, I made the gravity around 0.02, all signals are fixed but the CP! There is till oscillation in the power coefficient as follows:

Which is still strange because CP is a function of tip-speed ratio, and pitch angel that they are now fixed!
Thanks,
Best regards,
Sina

Dear Sina,

You can disable HydroDyn by setting CompHydro=0 in the FAST primary input file.

You haven’t given me enough information to debug the problem. Are you plotting the RtAeroCp output from AeroDyn v15 or something else? I would guess there is something in your simulation set-up that is causing an oscillation in aerodynamic loading.

Best regards,

Dear Dr. Jonkman,

Thanks for your prompt response. Yes, I am plotting the RtAeroCp output from AeroDyn v15, which I still don’t know what is the source of oscillation.

Thanks,
Best regards,
Sina

Dear Sina,

Do you see oscillations in other AeroDyn outputs, e.g. RtTSR, RtVAvgxh, and RtArea? Is RtSkew = 0?

Best regards,

Dear Dr. Jonkman,
Thanks again for your prompt response. Yes, I can see many oscillations in other output e.g RtArea. I don’t know about RtSkew. What is the role of it? Where can I find this flag?

Thanks,
Best regards,
Sina

Dear Sina,

If you are seeing oscillations in these outputs, then my guess is that you haven’t yet disabled all of the structural DOFs (in ElastoDyn).

RtSkew is an output parameter of AeroDyn v15 (just like RtArea is) and shows the skew angle between the inflow and rotor (from tilt or yaw).

Best regards,

Dear Dr. Jonkman,
Thanks for your fast response. Yes, I disabled all of them as follows:

and this is Rtskew:

Thanks
Best regards,
Sina

Dear Sina,

Do you have BeamDyn enabled (meaning the blades are modeled structural by BeamDyn, not ElastoDyn)–as specified in the OpenFAST glue code?

Do you have nonzero shaft tilt or nacelle-yaw (as specified in ElastoDyn) or nonzero veer or wind direction (as specified in InflowWind)?

Best regards,

## Dear Dr. Jonkman, This is my BeamDyn: --------- BEAMDYN V1.01.* INPUT FILE ------------------------------------------- NREL 5MW blade ---------------------- SIMULATION CONTROL -------------------------------------- False Echo - Echo input data to “.ech” (flag) 2 analysis_type - 1: Static analysis; 2: Dynamic analysis 0.0 rhoinf - Numerical Damping Parameter for Generalized-alpha integrator 2 quadrature - 1: Gauss; 2: Trapezoidal DEFAULT refine - Refinement factor for quadrature 2. DEFAULT = 1 DEFAULT n_fact - Factorization frequency: The Jacobian is computed every n_fact steps in N-R iteration. DEFAULT = 5 DEFAULT DTBeam - Time step size DEFAULT NRMax - Max number of iterations in Newton-Ralphson algorithm DEFAULT stop_tol - Tolerance for stopping criterion ---------------------- GEOMETRY PARAMETER -------------------------------------- 1 member_total - Total number of member (-) 49 kp_total - Total number of key point (-) 1 49 - Member number; Number of key points in this member kp_xr kp_yr kp_zr initial_twist (m) (m) (m) (deg) 0.000000 0.000000 0.000000 13.308000 0.000000 0.000000 0.199875 13.308000 0.000000 0.000000 1.199865 13.308000 0.000000 0.000000 2.199855 13.308000 0.000000 0.000000 3.199845 13.308000 0.000000 0.000000 4.199835 13.308000 0.000000 0.000000 5.199825 13.308000 0.000000 0.000000 6.199815 13.308000 0.000000 0.000000 7.199805 13.308000 0.000000 0.000000 8.201025 13.308000 0.000000 0.000000 9.199785 13.308000 0.000000 0.000000 10.199775 13.308000 0.000000 0.000000 11.199765 13.181000 0.000000 0.000000 12.199755 12.848000 0.000000 0.000000 13.200975 12.192000 0.000000 0.000000 14.199735 11.561000 0.000000 0.000000 15.199725 11.072000 0.000000 0.000000 16.199715 10.792000 0.000000 0.000000 18.200925 10.232000 0.000000 0.000000 20.200290 9.672000 0.000000 0.000000 22.200270 9.110000 0.000000 0.000000 24.200250 8.534000 0.000000 0.000000 26.200230 7.932000 0.000000 0.000000 28.200825 7.321000 0.000000 0.000000 30.200190 6.711000 0.000000 0.000000 32.200170 6.122000 0.000000 0.000000 34.200150 5.546000 0.000000 0.000000 36.200130 4.971000 0.000000 0.000000 38.200725 4.401000 0.000000 0.000000 40.200090 3.834000 0.000000 0.000000 42.200070 3.332000 0.000000 0.000000 44.200050 2.890000 0.000000 0.000000 46.200030 2.503000 0.000000 0.000000 48.201240 2.116000 0.000000 0.000000 50.199990 1.730000 0.000000 0.000000 52.199970 1.342000 0.000000 0.000000 54.199950 0.954000 0.000000 0.000000 55.199940 0.760000 0.000000 0.000000 56.199930 0.574000 0.000000 0.000000 57.199920 0.404000 0.000000 0.000000 57.699915 0.319000 0.000000 0.000000 58.201140 0.253000 0.000000 0.000000 58.699905 0.216000 0.000000 0.000000 59.199900 0.178000 0.000000 0.000000 59.699895 0.140000 0.000000 0.000000 60.199890 0.101000 0.000000 0.000000 60.699885 0.062000 0.000000 0.000000 61.199880 0.023000 0.000000 0.000000 61.500000 0.000000 ---------------------- MESH PARAMETER ------------------------------------------ 5 order_elem - Order of interpolation (basis) function (-) ---------------------- MATERIAL PARAMETER -------------------------------------- “NRELOffshrBsline5MW_BeamDyn_Blade.dat” BldFile - Name of file containing properties for blade ---------------------- PITCH ACTUATOR PARAMETERS ------------------------------- False UsePitchAct - Whether a pitch actuator should be used (flag) 200 PitchJ - Pitch actuator inertia (kg-m^2) [used only when UsePitchAct is true] 2.0E+7 PitchK - Pitch actuator stiffness (kg-m^2/s^2) [used only when UsePitchAct is true] 5.0E+5 PitchC - Pitch actuator damping (kg-m^2/s) [used only when UsePitchAct is true] ---------------------- OUTPUTS ------------------------------------------------- True SumPrint - Print summary data to “.sum” (flag) “ES10.3E2” OutFmt - Format used for text tabular output, excluding the time channel. Resulting field should be 10 characters. (quoted string) 0 NNodeOuts - Number of nodes to output to file [0 - 9] (-) 1,2,3,4,5,6 OutNd - 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, (-) “RootFxr, RootFyr, RootFzr” “RootMxr, RootMyr, RootMzr” “TipTDxr, TipTDyr, TipTDzr” “TipRDxr, TipRDyr, TipRDzr” END of input file (the word “END” must appear in the first 3 columns of this last OutList line)

Regarding the shaft tilt, and nacelle-yaw they both are zero. And this is my windinflow input file:

## False Echo - Echo input data to .ech (flag) 2 WindType - switch for wind file type (1=steady; 2=uniform; 3=binary TurbSim FF; 4=binary Bladed-style FF; 5=HAWC format; 6=User defined) 0 PropagationDir - Direction of wind propagation (meteoroligical rotation from aligned with X (positive rotates towards -Y) – degrees) 1 NWindVel - Number of points to output the wind velocity (0 to 9) 0 WindVxiList - List of coordinates in the inertial X direction (m) 0 WindVyiList - List of coordinates in the inertial Y direction (m) 90 WindVziList - List of coordinates in the inertial Z direction (m) ================== Parameters for Steady Wind Conditions [used only for WindType = 1] ========================= 0 HWindSpeed - Horizontal windspeed (m/s) 90 RefHt - Reference height for horizontal wind speed (m) 0.2 PLexp - Power law exponent (-) ================== Parameters for Uniform wind file [used only for WindType = 2] ============================ “Step-Wind.wnd” Filename - Filename of time series data for uniform wind field. (-) 90 RefHt - Reference height for horizontal wind speed (m) 125.88 RefLength - Reference length for linear horizontal and vertical sheer (-) ================== Parameters for Binary TurbSim Full-Field files [used only for WindType = 3] ============== “TurbSim_Hydro.bts” Filename - Name of the Full field wind file to use (.bts) ================== Parameters for Binary Bladed-style Full-Field files [used only for WindType = 4] ========= “Turbsim_Hydro.twr” FilenameRoot - Rootname of the full-field wind file to use (.wnd, .sum) True TowerFile - Have tower file (.twr) (flag) ================== Parameters for HAWC-format binary files [Only used with WindType = 5] ===================== “wasp\Output\basic_5u.bin” FileName_u - name of the file containing the u-component fluctuating wind (.bin) “wasp\Output\basic_5v.bin” FileName_v - name of the file containing the v-component fluctuating wind (.bin) “wasp\Output\basic_5w.bin” FileName_w - name of the file containing the w-component fluctuating wind (.bin) 64 nx - number of grids in the x direction (in the 3 files above) (-) 32 ny - number of grids in the y direction (in the 3 files above) (-) 32 nz - number of grids in the z direction (in the 3 files above) (-) 16 dx - distance (in meters) between points in the x direction (m) 3 dy - distance (in meters) between points in the y direction (m) 3 dz - distance (in meters) between points in the z direction (m) 90 RefHt - reference height; the height (in meters) of the vertical center of the grid (m) ------------- Scaling parameters for turbulence --------------------------------------------------------- 1 ScaleMethod - Turbulence scaling method [0 = none, 1 = direct scaling, 2 = calculate scaling factor based on a desired standard deviation] 1 SFx - Turbulence scaling factor for the x direction (-) [ScaleMethod=1] 1 SFy - Turbulence scaling factor for the y direction (-) [ScaleMethod=1] 1 SFz - Turbulence scaling factor for the z direction (-) [ScaleMethod=1] 12 SigmaFx - Turbulence standard deviation to calculate scaling from in x direction (m/s) [ScaleMethod=2] 8 SigmaFy - Turbulence standard deviation to calculate scaling from in y direction (m/s) [ScaleMethod=2] 2 SigmaFz - Turbulence standard deviation to calculate scaling from in z direction (m/s) [ScaleMethod=2] ------------- Mean wind profile parameters (added to HAWC-format files) --------------------------------- 5 URef - Mean u-component wind speed at the reference height (m/s) 2 WindProfile - Wind profile type (0=constant;1=logarithmic,2=power law) 0.2 PLExp - Power law exponent (-) (used for PL wind profile type only) 0.03 Z0 - Surface roughness length (m) (used for LG wind profile type only) ====================== OUTPUT ================================================== False SumPrint - Print summary data to .IfW.sum (flag) OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels, (-) “Wind1VelX” X-direction wind velocity at point WindList(1) “Wind1VelY” Y-direction wind velocity at point WindList(1) “Wind1VelZ” Z-direction wind velocity at point WindList(1) END of input file (the word “END” must appear in the first 3 columns of this last OutList line)

Thanks
Best regards
Sina

Dear Sina,

You can’t disable the blade structural DOFs in BeamDyn, so, your rotor is not rigid. To make it rigid, I would disable BeamDyn in the OpenFAST primary input file (meaning the blade structure is modeled in ElastoDyn, and you’ve disabled those DOFs).

What does your InfloWind input file look like?

Best regards,

## False Echo - Echo input data to .ech (flag) 2 WindType - switch for wind file type (1=steady; 2=uniform; 3=binary TurbSim FF; 4=binary Bladed-style FF; 5=HAWC format; 6=User defined) 0 PropagationDir - Direction of wind propagation (meteoroligical rotation from aligned with X (positive rotates towards -Y) – degrees) 1 NWindVel - Number of points to output the wind velocity (0 to 9) 0 WindVxiList - List of coordinates in the inertial X direction (m) 0 WindVyiList - List of coordinates in the inertial Y direction (m) 90 WindVziList - List of coordinates in the inertial Z direction (m) ================== Parameters for Steady Wind Conditions [used only for WindType = 1] ========================= 0 HWindSpeed - Horizontal windspeed (m/s) 90 RefHt - Reference height for horizontal wind speed (m) 0.2 PLexp - Power law exponent (-) ================== Parameters for Uniform wind file [used only for WindType = 2] ============================ “Step-Wind.wnd” Filename - Filename of time series data for uniform wind field. (-) 90 RefHt - Reference height for horizontal wind speed (m) 125.88 RefLength - Reference length for linear horizontal and vertical sheer (-) ================== Parameters for Binary TurbSim Full-Field files [used only for WindType = 3] ============== “TurbSim_Hydro.bts” Filename - Name of the Full field wind file to use (.bts) ================== Parameters for Binary Bladed-style Full-Field files [used only for WindType = 4] ========= “Turbsim_Hydro.twr” FilenameRoot - Rootname of the full-field wind file to use (.wnd, .sum) True TowerFile - Have tower file (.twr) (flag) ================== Parameters for HAWC-format binary files [Only used with WindType = 5] ===================== “wasp\Output\basic_5u.bin” FileName_u - name of the file containing the u-component fluctuating wind (.bin) “wasp\Output\basic_5v.bin” FileName_v - name of the file containing the v-component fluctuating wind (.bin) “wasp\Output\basic_5w.bin” FileName_w - name of the file containing the w-component fluctuating wind (.bin) 64 nx - number of grids in the x direction (in the 3 files above) (-) 32 ny - number of grids in the y direction (in the 3 files above) (-) 32 nz - number of grids in the z direction (in the 3 files above) (-) 16 dx - distance (in meters) between points in the x direction (m) 3 dy - distance (in meters) between points in the y direction (m) 3 dz - distance (in meters) between points in the z direction (m) 90 RefHt - reference height; the height (in meters) of the vertical center of the grid (m) ------------- Scaling parameters for turbulence --------------------------------------------------------- 1 ScaleMethod - Turbulence scaling method [0 = none, 1 = direct scaling, 2 = calculate scaling factor based on a desired standard deviation] 1 SFx - Turbulence scaling factor for the x direction (-) [ScaleMethod=1] 1 SFy - Turbulence scaling factor for the y direction (-) [ScaleMethod=1] 1 SFz - Turbulence scaling factor for the z direction (-) [ScaleMethod=1] 12 SigmaFx - Turbulence standard deviation to calculate scaling from in x direction (m/s) [ScaleMethod=2] 8 SigmaFy - Turbulence standard deviation to calculate scaling from in y direction (m/s) [ScaleMethod=2] 2 SigmaFz - Turbulence standard deviation to calculate scaling from in z direction (m/s) [ScaleMethod=2] ------------- Mean wind profile parameters (added to HAWC-format files) --------------------------------- 5 URef - Mean u-component wind speed at the reference height (m/s) 2 WindProfile - Wind profile type (0=constant;1=logarithmic,2=power law) 0.2 PLExp - Power law exponent (-) (used for PL wind profile type only) 0.03 Z0 - Surface roughness length (m) (used for LG wind profile type only) ====================== OUTPUT ================================================== False SumPrint - Print summary data to .IfW.sum (flag) OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels, (-) “Wind1VelX” X-direction wind velocity at point WindList(1) “Wind1VelY” Y-direction wind velocity at point WindList(1) “Wind1VelZ” Z-direction wind velocity at point WindList(1) END of input file (the word “END” must appear in the first 3 columns of this last OutList line)

Regarding the BeamDyn, I didn’t touch the BeamDyn file. I sent it to you as it is. Could you clarify it more?

Thanks,
Best regards,
Sina

Dear Sina,

What is in “Step-Wind.wnd”?

To disable BeamDyn, set CompElast=1 in the FAST primary input file.

Best regards,

Dear Dr. Jonkman,
Thanks for responding me with celerity. This is my step_wind file:

! Time Wind Wind Vert. Horiz. Vert. LinV Gust
! Speed Dir Speed Shear LinV Speed Speed
0.0 22 0.0 0.0 0.0 0.0 0.0 0.0
0.1 22 0.0 0.0 0.0 0.0 0.0 0.0

Regarding BeamDyn, I could not find CompElast flag in the ElastoDyn. Could you tell me in which file it is located?
Thanks
Best regards,
Sina

Dear Sina,

OK, I see that you are using steady, uniform wind of 22 m/s.

CompElast is set in the FAST primary input (*.fst) file.

Best regards,