Tower base loads due wind effect

Discuss the theory and modeling of rotor aerodynamics.

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Riccardo.Caradonna
Posts: 34
Joined: Mon May 04, 2020 3:31 am
Organization: Politecnico di Torino
Location: Italia

Tower base loads due wind effect

Postby Riccardo.Caradonna » Mon May 04, 2020 3:14 pm

Hello everyone,

for my master thesis I developed a model for offshore wind turbines. I just noticed some discrepance between tower base forces calculated with my model and those of FAST v8.16.00a-bjj.
To solve the problem I tried how these forces are calculated in FAST, but I could not find anything, can you suggest me a document that can help me?
In particular I'm running a Test 18 with:
-steady wind of 10 m/s,
-all DOF set to "FALSE", except drivetrain and generator DOF;

and the TwrBsFyt has an oscillatory trend, so I can't understand what this force depends on.

Thank you,
Riccardo.

Jason.Jonkman
Posts: 5738
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Tower base loads due wind effect

Postby Jason.Jonkman » Mon May 04, 2020 4:38 pm

Dear Riccardo,

For information on the FAST theory basis, please see the following forum topic: viewtopic.php?f=4&t=424. That said, much of that doesn't apply when all DOFs are disabled except the drivetrain and generator DOF.

Are you using steady uniform wind without yaw error? Even so, the NREL 5-MW turbine has some rotor tilt, which may lead to oscillations in aerodynamic loads. I'd probably have to know more about your simulation setup and results to comment more.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Riccardo.Caradonna
Posts: 34
Joined: Mon May 04, 2020 3:31 am
Organization: Politecnico di Torino
Location: Italia

Re: Tower base loads due wind effect

Postby Riccardo.Caradonna » Tue May 05, 2020 9:45 am

Dear Jason,

Thanks for your prompt reply. As you requested the results of: TwrBsFxt, TwrBsFyt, TwrBsFzt; are shown in "Force" attachment.
Moreover, the wind trends in each direction are shown in the "Wind" attachment.
While the input files used for this Test are are the follow.

------- ELASTODYN v1.03.* INPUT FILE -------------------------------------------
NREL 5.0 MW Baseline Wind Turbine for Use in Offshore Analysis. Properties from Dutch Offshore Wind Energy Converter (DOWEC) 6MW Pre-Design (10046_009.pdf) and REpower 5M 5MW (5m_uk.pdf)
---------------------- SIMULATION CONTROL --------------------------------------
False Echo - Echo input data to "<RootName>.ech" (flag)
3 Method - Integration method: {1: RK4, 2: AB4, or 3: ABM4} (-)
"DEFAULT" DT - Integration time step (s)
---------------------- ENVIRONMENTAL CONDITION ---------------------------------
9.80665 Gravity - Gravitational acceleration (m/s^2)
---------------------- DEGREES OF FREEDOM --------------------------------------
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]
True DrTrDOF - Drivetrain rotational-flexibility DOF (flag)
True GenDOF - Generator DOF (flag)
False 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)
False PtfmSgDOF - Platform horizontal surge translation DOF (flag)
False PtfmSwDOF - Platform horizontal sway translation DOF (flag)
False PtfmHvDOF - Platform vertical heave translation DOF (flag)
False PtfmRDOF - Platform roll tilt rotation DOF (flag)
False PtfmPDOF - Platform pitch tilt rotation DOF (flag)
False 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)
6.364 BlPitch(1) - Blade 1 initial pitch (degrees)
6.364 BlPitch(2) - Blade 2 initial pitch (degrees)
6.364 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)
8.1344 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)
---------------------- TURBINE CONFIGURATION -----------------------------------
3 NumBl - Number of blades (-)
63 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)
0 PreCone(1) - Blade 1 cone angle (degrees)
0 PreCone(2) - Blade 2 cone angle (degrees)
0 PreCone(3) - Blade 3 cone angle (degrees) [unused for 2 blades]
0 HubCM - Distance from rotor apex to hub mass [positive downwind] (meters)
0 UndSling - Undersling length [distance from teeter pin to the rotor apex] (meters) [unused for 3 blades]
0 Delta3 - Delta-3 angle for teetering rotors (degrees) [unused for 3 blades]
0 AzimB1Up - Azimuth value to use for I/O when blade 1 points up (degrees)
-5 OverHang - Distance from yaw axis to rotor apex [3 blades] or teeter pin [2 blades] (meters)
1.912 ShftGagL - Distance from rotor apex [3 blades] or teeter pin [2 blades] to shaft strain gages [positive for upwind rotors] (meters)
0 ShftTilt - Rotor shaft tilt angle (degrees)
1.9 NacCMxn - Downwind distance from the tower-top to the nacelle CM (meters)
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)
-3.09528 NcIMUxn - Downwind distance from the tower-top to the nacelle IMU (meters)
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)
2 Twr2Shft - Vertical distance from the tower-top to the rotor shaft (meters)
87.6 TowerHt - Height of tower above ground level [onshore] or MSL [offshore] (meters)
0 TowerBsHt - Height of tower base above ground level [onshore] or MSL [offshore] (meters)
0 PtfmCMxt - Downwind distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
0 PtfmCMyt - Lateral distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
0 PtfmCMzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
0 PtfmRefzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform reference point (meters)
---------------------- MASS AND INERTIA ----------------------------------------
0 TipMass(1) - Tip-brake mass, blade 1 (kg)
0 TipMass(2) - Tip-brake mass, blade 2 (kg)
0 TipMass(3) - Tip-brake mass, blade 3 (kg) [unused for 2 blades]
56780 HubMass - Hub mass (kg)
115926 HubIner - Hub inertia about rotor axis [3 blades] or teeter axis [2 blades] (kg m^2)
534.116 GenIner - Generator inertia about HSS (kg m^2)
240000 NacMass - Nacelle mass (kg)
2.60789E+06 NacYIner - Nacelle inertia about yaw axis (kg m^2)
0 YawBrMass - Yaw bearing mass (kg)
0 PtfmMass - Platform mass (kg)
0 PtfmRIner - Platform inertia for roll tilt rotation about the platform CM (kg m^2)
0 PtfmPIner - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)
0 PtfmYIner - Platform inertia for yaw rotation about the platform CM (kg m^2)
---------------------- BLADE ---------------------------------------------------
17 BldNodes - Number of blade nodes (per blade) used for analysis (-)
"NRELOffshrBsline5MW_Blade.dat" BldFile(1) - Name of file containing properties for blade 1 (quoted string)
"NRELOffshrBsline5MW_Blade.dat" BldFile(2) - Name of file containing properties for blade 2 (quoted string)
"NRELOffshrBsline5MW_Blade.dat" BldFile(3) - Name of file containing properties for blade 3 (quoted string) [unused for 2 blades]
---------------------- 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 TeetDmpP - Rotor-teeter damper position (degrees) [used only for 2 blades and when TeetMod=1]
0 TeetDmp - Rotor-teeter damping constant (N-m/(rad/s)) [used only for 2 blades and when TeetMod=1]
0 TeetCDmp - Rotor-teeter rate-independent Coulomb-damping moment (N-m) [used only for 2 blades and when TeetMod=1]
0 TeetSStP - Rotor-teeter soft-stop position (degrees) [used only for 2 blades and when TeetMod=1]
0 TeetHStP - Rotor-teeter hard-stop position (degrees) [used only for 2 blades and when TeetMod=1]
0 TeetSSSp - Rotor-teeter soft-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
0 TeetHSSp - Rotor-teeter hard-stop linear-spring constant (N-m/rad) [used only for 2 blades and when TeetMod=1]
---------------------- DRIVETRAIN ----------------------------------------------
100 GBoxEff - Gearbox efficiency (%)
97 GBRatio - Gearbox ratio (-)
8.67637E+08 DTTorSpr - Drivetrain torsional spring (N-m/rad)
5.900E+06 DTTorDmp - Drivetrain torsional damper (N-m/(rad/s))
---------------------- FURLING -------------------------------------------------
False Furling - Read in additional model properties for furling turbine (flag) [must currently be FALSE)
"unused" FurlFile - Name of file containing furling properties (quoted string) [unused when Furling=False]
---------------------- TOWER ---------------------------------------------------
20 TwrNodes - Number of tower nodes used for analysis (-)
"NRELOffshrBsline5MW_Onshore_ElastoDyn_Tower.dat" TwrFile - Name of file containing tower properties (quoted string)
---------------------- OUTPUT --------------------------------------------------
True SumPrint - Print summary data to "<RootName>.sum" (flag)
1 OutFile - Switch to determine where output will be placed: {1: in module output file only; 2: in glue code output file only; 3: both} (currently unused)
True TabDelim - Use tab delimiters in text tabular output file? (flag) (currently unused)
"ES10.3E2" OutFmt - Format used for text tabular output (except time). Resulting field should be 10 characters. (quoted string) (currently unused)
0 TStart - Time to begin tabular output (s) (currently unused)
1 DecFact - Decimation factor for tabular output {1: output every time step} (-) (currently unused)
0 NTwGages - Number of tower nodes that have strain gages for output [0 to 9] (-)
10, 19, 28 TwrGagNd - List of tower nodes that have strain gages [1 to TwrNodes] (-) [unused if NTwGages=0]
3 NBlGages - Number of blade nodes that have strain gages for output [0 to 9] (-)
5, 9, 13 BldGagNd - List of blade nodes that have strain gages [1 to BldNodes] (-) [unused if NBlGages=0]
OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels, (-)
"OoPDefl1" - Blade 1 out-of-plane and in-plane deflections and tip twist
"IPDefl1" - Blade 1 out-of-plane and in-plane deflections and tip twist
"TwstDefl1" - Blade 1 out-of-plane and in-plane deflections and tip twist
"BldPitch1" - Blade 1 pitch angle
"Azimuth" - Blade 1 azimuth angle
"RotSpeed" - Low-speed shaft and high-speed shaft speeds
"GenSpeed" - Low-speed shaft and high-speed shaft speeds
"TTDspFA" - Tower fore-aft and side-to-side displacements and top twist
"TTDspSS" - Tower fore-aft and side-to-side displacements and top twist
"TTDspTwst" - Tower fore-aft and side-to-side displacements and top twist
"NacYaw" - Nacelle yaw angle and nacelle yaw error estimate

"RootFxb1" - Out-of-plane shear, in-plane shear, and axial forces at the root of blade 1
"RootFyb1" - Out-of-plane shear, in-plane shear, and axial forces at the root of blade 1
"RootFzb1" - Out-of-plane shear, in-plane shear, and axial forces at the root of blade 1
"RootMxb1" - In-plane bending, out-of-plane bending, and pitching moments at the root of blade 1
"RootMyb1" - In-plane bending, out-of-plane bending, and pitching moments at the root of blade 1
"RootMzb1" - In-plane bending, out-of-plane bending, and pitching moments at the root of blade 1
"RotTorq" - Rotor torque and low-speed shaft 0- and 90-bending moments at the main bearing
"RotThrust"
"YawBrFxp" - Fore-aft shear, side-to-side shear, and vertical forces at the top of the tower (not rotating with nacelle yaw)
"YawBrFyp" - Fore-aft shear, side-to-side shear, and vertical forces at the top of the tower (not rotating with nacelle yaw)
"YawBrFzp" - Fore-aft shear, side-to-side shear, and vertical forces at the top of the tower (not rotating with nacelle yaw)
"YawBrMxp" - Side-to-side bending, fore-aft bending, and yaw moments at the top of the tower (not rotating with nacelle yaw)
"YawBrMyp" - Side-to-side bending, fore-aft bending, and yaw moments at the top of the tower (not rotating with nacelle yaw)
"YawBrMzp" - Side-to-side bending, fore-aft bending, and yaw moments at the top of the tower (not rotating with nacelle yaw)
"TwrBsFxt" - Fore-aft shear, side-to-side shear, and vertical forces at the base of the tower (mudline)
"TwrBsFyt" - Fore-aft shear, side-to-side shear, and vertical forces at the base of the tower (mudline)
"TwrBsFzt" - Fore-aft shear, side-to-side shear, and vertical forces at the base of the tower (mudline)
"TwrBsMxt" - Side-to-side bending, fore-aft bending, and yaw moments at the base of the tower (mudline)
"TwrBsMyt" - Side-to-side bending, fore-aft bending, and yaw moments at the base of the tower (mudline)
"TwrBsMzt" - Side-to-side bending, fore-aft bending, and yaw moments at the base of the tower (mudline)
END of input file (the word "END" must appear in the first 3 columns of this last OutList line)
---------------------------------------------------------------------------------------


------- InflowWind v3.01.* INPUT FILE -------------------------------------------------------------------------
12 m/s turbulent winds on 31x31 FF grid and tower for FAST CertTests #18, #19, #21, #22, #23, and #24
---------------------------------------------------------------------------------------------------------------
False Echo - Echo input data to <RootName>.ech (flag)
1 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] =========================
10 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] ============================
"Wind/90m_12mps_twr.bin" 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] ==============
"Wind/Wind_NTM_B_13_v0h0.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] =========
"Wind/90m_12mps_twr" FilenameRoot - Rootname of the full-field wind file to use (.wnd, .sum)
False 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) ---------------------------------
10.151 URef - Mean u-component wind speed at the reference height (m/s)
0 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 <RootName>.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)
---------------------------------------------------------------------------------------


------- AERODYN v15.03.* INPUT FILE ------------------------------------------------
NREL 5.0 MW offshore baseline aerodynamic input properties.
====== General Options ============================================================================
False Echo - Echo the input to "<rootname>.AD.ech"? (flag)
"default" DTAero - Time interval for aerodynamic calculations {or "default"} (s)
1 WakeMod - Type of wake/induction model (switch) {0=none, 1=BEMT}
1 AFAeroMod - Type of blade airfoil aerodynamics model (switch) {1=steady model, 2=Beddoes-Leishman unsteady model}
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}
False TwrShadow – Calculate tower influence on wind based on downstream tower shadow? (flag)
False TwrAero - Calculate tower aerodynamic loads? (flag)
False FrozenWake - Assume frozen wake during linearization? (flag) [used only when WakeMod=1 and when linearizing]
====== Environmental Conditions ===================================================================
1.2 AirDens - Air density (kg/m^3)
1.464E-05 KinVisc - Kinematic air viscosity (m^2/s)
335 SpdSound - Speed of sound (m/s)
====== Blade-Element/Momentum Theory Options ====================================================== [used only when WakeMod=1]
2 SkewMod - Type of skewed-wake correction model (switch) {1=uncoupled, 2=Pitt/Peters, 3=coupled} [used only when WakeMod=1]
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]
"Default" IndToler - Convergence tolerance for BEMT nonlinear solve residual equation {or "default"} (-) [used only when WakeMod=1]
100 MaxIter - Maximum number of iteration steps (-) [used only when WakeMod=1]
====== Beddoes-Leishman Unsteady Airfoil Aerodynamics Options ===================================== [used only when AFAeroMod=2]
3 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]
====== Airfoil Information =========================================================================
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 (-)
8 NumAFfiles - Number of airfoil files used (-)
"Airfoils/Cylinder1.dat" AFNames - Airfoil file names (NumAFfiles lines) (quoted strings)
"Airfoils/Cylinder2.dat"
"Airfoils/DU40_A17.dat"
"Airfoils/DU35_A17.dat"
"Airfoils/DU30_A17.dat"
"Airfoils/DU25_A17.dat"
"Airfoils/DU21_A17.dat"
"Airfoils/NACA64_A17.dat"
====== Rotor/Blade Properties =====================================================================
True UseBlCm - Include aerodynamic pitching moment in calculations? (flag)
"NRELOffshrBsline5MW_AeroDyn_blade.dat" ADBlFile(1) - Name of file containing distributed aerodynamic properties for Blade #1 (-)
"NRELOffshrBsline5MW_AeroDyn_blade.dat" ADBlFile(2) - Name of file containing distributed aerodynamic properties for Blade #2 (-) [unused if NumBl < 2]
"NRELOffshrBsline5MW_AeroDyn_blade.dat" ADBlFile(3) - Name of file containing distributed aerodynamic properties for Blade #3 (-) [unused if NumBl < 3]
====== Tower Influence and Aerodynamics ============================================================= [used only when TwrPotent/=0, TwrShadow=True, or TwrAero=True]
12 NumTwrNds - Number of tower nodes used in the analysis (-) [used only when TwrPotent/=0, TwrShadow=True, or TwrAero=True]
TwrElev TwrDiam TwrCd
(m) (m) (-)
0.0000000E+00 6.0000000E+00 1.0000000E+00
8.5261000E+00 5.7870000E+00 1.0000000E+00
1.7053000E+01 5.5740000E+00 1.0000000E+00
2.5579000E+01 5.3610000E+00 1.0000000E+00
3.4105000E+01 5.1480000E+00 1.0000000E+00
4.2633000E+01 4.9350000E+00 1.0000000E+00
5.1158000E+01 4.7220000E+00 1.0000000E+00
5.9685000E+01 4.5090000E+00 1.0000000E+00
6.8211000E+01 4.2960000E+00 1.0000000E+00
7.6738000E+01 4.0830000E+00 1.0000000E+00
8.5268000E+01 3.8700000E+00 1.0000000E+00
8.7600000E+01 3.8700000E+00 1.0000000E+00
====== Outputs ====================================================================================
True SumPrint - Generate a summary file listing input options and interpolated properties to "<rootname>.AD.sum"? (flag)
0 NBlOuts - Number of blade node outputs [0 - 9] (-)
1, 9, 19 BlOutNd - Blade nodes whose values will be output (-)
0 NTwOuts - Number of tower node outputs [0 - 9] (-)
1, 2, 6 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, (-)
"RtAeroFxh"
"RtAeroFyh"
"RtAeroFzh"
"RtAeroMxh"
"RtAeroMyh"
"RtAeroMzh"
"RtAeroPwr"

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

Thank you for your help.

Best regards,
Riccardo.
Attachments
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Jason.Jonkman
Posts: 5738
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: Tower base loads due wind effect

Postby Jason.Jonkman » Tue May 05, 2020 10:59 am

Dear Riccardo,

I see an oscillation of about 30 cycles in 50 seconds, or 0.6 Hz. My guess is this is a 3P (3 per revolution) oscillation resulting from the 3-bladed rotor operating in the sheared (from the 0.2 power law shear exponent) and skewed flow (from the 5deg shaft tilt) that you have enabled.

Best regards.
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Riccardo.Caradonna
Posts: 34
Joined: Mon May 04, 2020 3:31 am
Organization: Politecnico di Torino
Location: Italia

Re: Tower base loads due wind effect

Postby Riccardo.Caradonna » Wed May 06, 2020 7:52 am

Dear Jason,

Thanks for your help, now the previsious ploblem is fixed.
Now I'm trying to extend the force analysis at not-steady state case. My model takes into account only the u-component of the wind, so there are differences between loads in the Z and Y directions due to the others two components of the wind developed by Turbsim (along y and z axis).
Can you suggest me any topic or document about how FAST V8 calculate these forces?
In other words, how can I find YawBrFyp and YawBrFzp from Wind1VelY and Wind1VelZ?

Best regards,

Riccardo.

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Re: Tower base loads due wind effect

Postby Jason.Jonkman » Wed May 06, 2020 9:09 am

Dear Riccardo,

Well, the transverse loads are impacted by the aerodynamic loads and structural response, including aero-elastic effects. I would suggest reviewing the FAST theory basis I referenced in the link in my post dated May 04, 2020 above.

Best regards
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

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Re: Tower base loads due wind effect

Postby Riccardo.Caradonna » Tue Sep 29, 2020 11:22 am

Dear Jason,

I am carrying out an Onshore test with test 24 with precon = 0, in particular I am finding it difficult to derive the wind values ​​in the tangential and normal directions with respect to the reference system of the blade.
To do the test I am using the wind files obtained from TurbSim, from which in addition to the .bts file to be implemented in the FAST test input file, I also extract the spatial and temporal distribution of the u, v, w components of the wind that I use then to verify.
To evaluate the wind components on the blade node, I use azimuth to evaluate the position of the node and the time to derive the wind spectrum corresponding to that time step.
Furthermore, to take into account the 3 wind components in the blade reference system, I use the following equation:

[Vx_blade Vy_blade Vz_blade]^T = (R^T) *([u v w]^T)
where is it:
_R is the rotation matrix shown in Figure 1 with (rx ry rz) respectively (Azimuth Pitch Yaw);


Normal speed (V_norm) is equal to Vx_blade while tangential speed (V_tang) is equal to Vy_blade + RotSpeed ​​* r.
Where r represents the radial position of the node.
Comparing the Vrel obtained as:
Vrel = sqrt (V_tang ^ 2 + V_norm ^ 2)
with the BαNβVrel output I do not find the same results.
Is there any error in my process?
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Re: Tower base loads due wind effect

Postby Jason.Jonkman » Tue Sep 29, 2020 11:59 am

Dear Riccardo,

A few comments and questions:
  • Are pitch and yaw associated with the floating platform or wind turbine?
  • Which structural DOFs are enabled in your model?
  • Which rotation sequence are you assuming?
  • The relative wind speed output from AeroDyn includes induction effects, which I don't see in your equation.
  • I would expect the relative wind speed (not including induction) in global to be V_wind - v_struct, but you have a + sign; I'm not sure if this is related to the coordinate system you are using.
I hope that helps.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Riccardo.Caradonna
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Re: Tower base loads due wind effect

Postby Riccardo.Caradonna » Tue Nov 03, 2020 10:18 am

Dear Jason,
I am verifying the BEM Theory implemented on my model, making comparisons with the FAST outputs.
I noticed some differences in the trends of pN and pT (normal and tangential load on the blade per unit of length), so I investigated more deeply, finding differences in the trends of a and a '(axial and tangential induction factor). From some tests I have found that the values ​​of Cx and Cy obtained by me are the same as those obtained by FAST, imposing the same alpha and phi inputs. Therefore the error must be in one of the three corrections; since the skew correction only concerns the axial induction factor, and since the tangential induction factor is also wrong, I focused on the other two corrections and on the value of a '. In my model I used the formulas shown in the following document https://www.nrel.gov/docs/fy15osti/63217.pdf
In particular, I note that in the first 4 nodes the tangential induction factor leaving FAST is 0, while according to my calculations, being
TIF = (sigma * Cy) / (4 * F * sinPhi * cosPhi - sigma * Cy)
and since sigma and Cy different from 0, and F not infinite, I don't understand how it manages to be TIF = 0 in the first 4 nodes.
Here are the FAST outputs I used:
Cx = 'BαNβCx'
Cy = 'BαNβCy'
AIF = a = 'BαNβAxInd'
TIF = a '=' BαNβTnInd '
Phi = 'BαNβPhi'
Alpha = 'BαNβAlpha'

Thanks for your help, best regards.

Riccardo.

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Re: Tower base loads due wind effect

Postby Jason.Jonkman » Tue Nov 03, 2020 12:05 pm

Dear Riccardo,

I'm not sure. There have been many changes to the BEM implementation in AeroDyn since the Ning et al paper you reference was published (to make the solution robust across all conditions, to make it compatible with the modularization framework, etc.). Unfortunately, I'm not ware of an updated reference that fully explains the current BEM algorithm. Your best bet is to review the AeroDyn source code to understand the algorithm. You may also want to run your model in debug mode to understand why your results differ.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

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Re: Tower base loads due wind effect

Postby Riccardo.Caradonna » Tue Nov 10, 2020 10:02 am

Dear Jason,
I am trying to evaluate the difference in wind speed in the various nodes of the blade between my model and FAST without induction, for the moment I am concentrating on the x direction. To do this I am using an Onshore test with an average wind of 8.5 with turbulence obtained from Turbsim (.bts file). To derive the wind from FAST I am using the BαNβVUndx output, since the test is onshore the x in the blade reference system is the same as the global reference system which is the one used by turbsim.
While in my model I created a spatially (X, Y) and temporally discretized look-up table, using the '.u' file out of Turbsim, then in the look-up table I enter with Time (T), Yposition (Y ) and Zposition (Z), where in the case of an onshore test:
T = current time-step;
Y = sin (Azimuth) * r;
Z = cos (Azimuth) * r.
Where is it:
Azimuth = is the output of FAST
r = distance in the z direction between the node under consideration and the center of the hub in the blade reference system.

Furthermore, in the FF_interp function present in the source code of the inflow wind, I noticed that FAST obtains the 4 pairs of points (Y, Z) relating to 2 Time slices and then performs bilinear interpolation for each time slice. Linear interpolation is then used to interpolate between time slices.
For this reason I have imposed a linear interpolation in my LUT in the three dimensions.
Despite this there are differences between my model and FAST, in particular I noticed that as the nodes increase, a time lag is created (fig. 1). This does not happen in the case of a steady wind with power law exponent (fig. 2) where my model and FAST are practically identical.
Is it possible that there is a difference between the '.u' and '.bts' files coming out of Turbsim?
Is there something wrong with my approach?

Thanks a lot for the help, best regards.

Riccardo.
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Re: Tower base loads due wind effect

Postby Bonnie.Jonkman » Tue Nov 10, 2020 10:58 am

Riccardo,

A few comments:
1. Some older versions of FAST/InflowWind did interpolation differently than the current version. It now does a tri-linear interpolation.
2. When InflowWind reads the FF grid files, it shifts them so that at time zero, the wind field starts half the grid width in front of the turbine. The initial X position is

Code: Select all

0.5*(NYGrids-1)*dY
.
3. Keep in mind that X=0 at the undeflected tower centerline (not at the hub). Depending on where you've requested output from InflowWind, this could make a difference.
4. You will need to calculate an X position as well as Y, Z, and time. Are your blades rigid? Do you have tilt or precone in your model? These will make a difference as to where the blade nodes are, and thus what the wind velocity will be. In the current InflowWind, it is calculated this way:

Code: Select all

TimeShifted = t_requested + ( InitialXPosition - X )/MeanFFWindSpeed
Bonnie Jonkman

Envision Energy USA, 2016-
National Renewable Energy Laboratory, 2003-2016

Riccardo.Caradonna
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Re: Tower base loads due wind effect

Postby Riccardo.Caradonna » Tue Nov 10, 2020 1:26 pm

Dear Bonnie,

Thank you for your prompt reply. Regarding your comments:
1. The inflow wind source code that I have read, I believe it is that of the FAST executive that I am using, because it was present in the folder I downloaded when I installed FAST v8.16.

3. In the test that I used I set overhang=0, so I think that the Hub is at the same x coordinate respect undeflected center line.

4. In this case I don't calculate the x position because is an onshore test, but in the other cases I calculate this position in my model to evaluate the time shifted (with the same equation you suggest). Moreover, my blades and tower are rigid and I set Tilt=0 and precone=0.

Regarding point 2, I have not set any shift in the x position. Do you think this can solve my problem? Could there be more?

Thank you again for your help, best regards.

Riccardo.

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Re: Tower base loads due wind effect

Postby Bonnie.Jonkman » Tue Nov 10, 2020 1:48 pm

I don't know how you have defined your nodes, but if you are matching at the hub node and NOT matching as you move out radially from the hub, I would suspect that there is an error in one or more of the position calculations.

Perhaps you can calculate the equivalent shift on your plot by matching the peaks and back-calculating how far it is off. Or just step through it using a debugger to identify differences.
Bonnie Jonkman

Envision Energy USA, 2016-
National Renewable Energy Laboratory, 2003-2016

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Re: Tower base loads due wind effect

Postby Riccardo.Caradonna » Thu Nov 12, 2020 2:09 pm

Dear Bonnie,

With the imposition of an initial x value, the differences between the two graphs have decreased, but they are still present.
So to evaluate if, as you suggested, there is some error in evaluating the position of the nodes, I used 'Wind1VelX' as the output of FAST, so that it was a fixed point and that it was therefore comparable with what I get from Turbsim. To make the comparison, therefore, I set the coordinates of a node of the wind grid in the Inflowind input file. In this way I bypassed the node coordinates problem and therefore I expected an equal trend with only a time offset, due to the initial x value imposed in the Inflowind routine.
However, as you can see from figures 1 and 2, the analogous trend that I expected is obtained only for the hub coordinates (fig1), while if I move to the coordinates of another point of the grid (fig2), the differences do not they only limit more to the time offset.
Here is the Turbsim input file that I am using for the test:

Code: Select all

TurbSim Input File. Valid for TurbSim v1.06.00, 21-Sep-2012
 
---------Runtime Options-----------------------------------
1393911158               RandSeed1       - First random seed  (-2147483648 to 2147483647)
RANLUX              RandSeed2       - Second random seed (-2147483648 to 2147483647) for intrinsic pRNG, or an alternative pRNG: "RanLux" or "RNSNLW"
False                WrBHHTP         - Output hub-height turbulence parameters in binary form?  (Generates RootName.bin)
False               WrFHHTP         - Output hub-height turbulence parameters in formatted form?  (Generates RootName.dat)
False               WrADHH          - Output hub-height time-series data in AeroDyn form?  (Generates RootName.hh)
True               WrADFF          - Output full-field time-series data in TurbSim/AeroDyn form? (Generates Rootname.bts)
False               WrBLFF          - Output full-field time-series data in BLADED/AeroDyn form?  (Generates RootName.wnd)
False               WrADTWR         - Output tower time-series data? (Generates RootName.twr)
True               WrFMTFF         - Output full-field time-series data in formatted (readable) form?  (Generates RootName.u, RootName.v, RootName.w)
False               WrACT           - Output coherent turbulence time steps in AeroDyn form? (Generates RootName.cts)
True                Clockwise       - Clockwise rotation looking downwind? (used only for full-field binary files - not necessary for AeroDyn)
 0                  ScaleIEC        - Scale IEC turbulence models to exact target standard deviation? [0=no additional scaling; 1=use hub scale uniformly; 2=use individual scales]
 
--------Turbine/Model Specifications-----------------------
13                  NumGrid_Z       - Vertical grid-point matrix dimension
13                  NumGrid_Y       - Horizontal grid-point matrix dimension
0.05                TimeStep        - Time step [seconds]
1200                AnalysisTime    - Length of analysis time series [seconds] (program will add time if necessary: AnalysisTime = MAX(AnalysisTime, UsableTime+GridWidth/MeanHHWS) )
1200                UsableTime      - Usable length of output time series [seconds] (program will add GridWidth/MeanHHWS seconds)
90               HubHt           - Hub height [m] (should be > 0.5*GridHeight)
145.00              GridHeight      - Grid height [m]
145.00              GridWidth       - Grid width [m] (should be >= 2*(RotorRadius+ShaftLength))
0                   VFlowAng        - Vertical mean flow (uptilt) angle [degrees]
0                   HFlowAng        - Horizontal mean flow (skew) angle [degrees]
 
--------Meteorological Boundary Conditions-------------------
"IECKAI"            TurbModel       - Turbulence model ("IECKAI"=Kaimal, "IECVKM"=von Karman, "GP_LLJ", "NWTCUP", "SMOOTH", "WF_UPW", "WF_07D", "WF_14D", "TIDAL", or "NONE")
"3"             IECstandard     - Number of IEC 61400-x standard (x=1,2, or 3 with optional 61400-1 edition number (i.e. "1-Ed2") )
"B"                 IECturbc        - IEC turbulence characteristic ("A", "B", "C" or the turbulence intensity in percent) ("KHTEST" option with NWTCUP model, not used for other models)
"NTM"               IEC_WindType    - IEC turbulence type ("NTM"=normal, "xETM"=extreme turbulence, "xEWM1"=extreme 1-year wind, "xEWM50"=extreme 50-year wind, where x=wind turbine class 1, 2, or 3)
default             ETMc            - IEC Extreme Turbulence Model "c" parameter [m/s]
"PL"             WindProfileType - Wind profile type ("JET";"LOG"=logarithmic;"PL"=power law;"H2L"=Log law for TIDAL spectral model;"IEC"=PL on rotor disk, LOG elsewhere; or "default")
90                   RefHt           - Height of the reference wind speed [m]
8.5                URef            - Mean (total) wind speed at the reference height [m/s] (or "default" for JET wind profile)
default             ZJetMax         - Jet height [m] (used only for JET wind profile, valid 70-490 m)
0.14                PLExp           - Power law exponent [-] (or "default")   
0.03                Z0              - Surface roughness length [m] (or "default")
 
--------Non-IEC Meteorological Boundary Conditions------------
default             Latitude        - Site latitude [degrees] (or "default")
0.05                RICH_NO         - Gradient Richardson number
default             UStar           - Friction or shear velocity [m/s] (or "default")
default             ZI              - Mixing layer depth [m] (or "default")
default             PC_UW           - Hub mean u'w' Reynolds stress (or "default")
default             PC_UV           - Hub mean u'v' Reynolds stress (or "default")
default             PC_VW           - Hub mean v'w' Reynolds stress (or "default")
default             IncDec1         - u-component coherence parameters (e.g. "10.0  0.3e-3" in quotes) (or "default")
default             IncDec2         - v-component coherence parameters (e.g. "10.0  0.3e-3" in quotes) (or "default")
default             IncDec3         - w-component coherence parameters (e.g. "10.0  0.3e-3" in quotes) (or "default")
default             CohExp          - Coherence exponent (or "default")

--------Coherent Turbulence Scaling Parameters-------------------
"C:\Users\Luigi\Dropbox\Tesi\NREL\Turbsim\coh_events\EventData\"  CTEventPath     - Name of the path where event data files are located
"Random"            CTEventFile     - Type of event files ("LES", "DNS", or "RANDOM")
true                Randomize       - Randomize the disturbance scale and locations? (true/false)
 1.0                DistScl         - Disturbance scale (ratio of wave height to rotor disk). (Ignored when Randomize = true.)
 0.5                CTLy            - Fractional location of tower centerline from right (looking downwind) to left side of the dataset. (Ignored when Randomize = true.)
 0.5                CTLz            - Fractional location of hub height from the bottom of the dataset. (Ignored when Randomize = true.)
30.0                CTStartTime     - Minimum start time for coherent structures in RootName.cts [seconds]

==================================================
NOTE: Do not add or remove any lines in this file!
==================================================

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