Hi everyone, I am working on the modal analysis of the turbine tower. However, I have some confusion on fore-aft vibration modelling and the related output data from FAST.
After enabling both the first and second modein ElastoDyn.dat, I obtained the output from the tower gages (TwHt1ALxt-TwHt9ALxt ), and the tower top acceleration (YawBrTAxp) for the fore-aft vibration. And then implement an power spectural density analysis on the data. My confusion is that there is two peaks in the PSD of the tower gages data, while only one peak for the first mode in the PSD of ‘YawBrRAxp’. (Show in the left column in the figure).
And I also try to enable only one mode, the first and the second, and then derive PSD of the ‘YawBrTAxp’. And I can derive the two peaks corresponding to the first and second mode, respetively. But if I enable both two modes, again there is only one peak in the PSD. (Shown in the right column in the figure).
So I am confused on these results. I would expect to get two peaks corresponding to two modes from the tower-top measurement as in the tower gages. Does this expectation make sense? And should I make some more modification on the ‘ElastoDyn.dat’ file? (the current one is also attached here)
And I am also wondering how FAST derives the acceleration while both two modes are enabled. (Since it seems that it is not simply adding two modes together). Is there references for the theory part?
(The data sampling time is 0.01s in the simulation. The wind speed is step steady wind at 10m/s, the controller is the k_omega_Square torque controller.)
Thanks in advance for your help!
Best regards
The details of ElastroDyn.dat are as below:
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)
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)
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)
0.0000 BlPitch(1) - Blade 1 initial pitch (degrees)
0.0000 BlPitch(2) - Blade 2 initial pitch (degrees)
0.0000 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)
9.2 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 (-)
63.0000 TipRad - The distance from the rotor apex to the blade tip (meters)
1.5000 HubRad - The distance from the rotor apex to the blade root (meters)
-2.5 PreCone(1) - Blade 1 cone angle (degrees)
-2.5 PreCone(2) - Blade 2 cone angle (degrees)
-2.5 PreCone(3) - Blade 3 cone angle (degrees) [unused for 2 blades]
0 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)
-5.01910 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)
-5.0 ShftTilt - Rotor shaft tilt angle (degrees)
1.90000 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)
2.40000 Twr2Shft - Vertical distance from the tower-top to the rotor shaft (meters)
87.60 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]
5.678E+04 HubMass - Hub mass (kg)
1.159E+05 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)
2.400E+05 NacMass - Nacelle mass (kg)
2.599E+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 ---------------------------------------------------
48 BldNodes - Number of blade nodes (per blade) used for analysis (-)
"ElastoDyn_blade.dat" BldFile(1) - Name of file containing properties for blade 1 (quoted string)
"ElastoDyn_blade.dat" BldFile(2) - Name of file containing properties for blade 2 (quoted string)
"ElastoDyn_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 ----------------------------------------------
100.0 GBoxEff - Gearbox efficiency (%)
97.0 GBRatio - Gearbox ratio (-)
8.67637E+08 DTTorSpr - Drivetrain torsional spring (N-m/rad)
6.215E+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 ---------------------------------------------------
40 TwrNodes - Number of tower nodes used for analysis (-)
"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)
9 NTwGages - Number of tower nodes that have strain gages for output [0 to 9] (-)
1, 2, 3, 4, 5, 6, 7, 8, 9 TwrGagNd - List of tower nodes that have strain gages [1 to TwrNodes] (-) [unused if NTwGages=0]
0 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"
"OoPDefl2"
"OoPDefl3"
"IPDefl1"
"IPDefl2"
"IPDefl3"
"NcIMUTAxs"
"NcIMUTAys"
"NcIMUTAzs"
"NcIMUTVxs"
"NcIMUTVys"
"NcIMUTVzs"
"NcIMURAxs"
"NcIMURAys"
"NcIMURAzs"
"RootMOoP1"
"RootMOoP2"
"RootMOoP3"
"RootMIP1"
"RootMIP2"
"RootMIP3"
"RootMFlp1"
"RootMFlp2"
"RootMFlp3"
"RootMEdg1"
"RootMEdg2"
"RootMEdg3"
"TwrBsMxt"
"TwrBsMyt"
"TwrBsMzt"
"LSSTipMya"
"LSSTipMza"
"LSSTipVxa"
"GenSpeed"
"BlPitch1"
"BlPitch2"
"BlPitch3"
"Azimuth"
"RotPwr"
"RotThrust"
"RotSpeed"
"HSShftTq"
"LSShftFya"
"LSShftFza"
"LSShftFys"
"LSShftFzs"
"YawBrFyp"
"YawBrTDyt"
"RotTorq"
"TwHt1ALxt"
"TwHt1ALyt"
"TwHt2ALxt"
"TwHt2ALyt"
"TwHt3ALxt"
"TwHt3ALyt"
"TwHt4ALxt"
"TwHt4ALyt"
"TwHt5ALxt"
"TwHt5ALyt"
"TwHt6ALxt"
"TwHt6ALyt"
"TwHt7ALxt"
"TwHt7ALyt"
"TwHt8ALxt"
"TwHt8ALyt"
"TwHt9ALxt"
"TwHt9ALyt"
"TwHt1TDxt"
"TwHt1TDYt"
"TwHt2TDxt"
"TwHt2TDyt"
"TwHt3TDxt"
"TwHt3TDyt"
"TwHt4TDxt"
"TwHt4TDyt"
"TwHt5TDxt"
"TwHt5TDyt"
"TwHt6TDxt"
"TwHt6TDyt"
"TwHt7TDxt"
"TwHt7TDyt"
"TwHt8TDxt"
"TwHt8TDyt"
"TwHt9TDxt"
"TwHt9TDyt"
"YawBrTDxp"
"YawBrTDyp"
"YawBrTDzp"
"YawBrTDxt"
"YawBrTDyt"
"YawBrTDzt"
"YawBrTAxp"
"YawBrTAyp"
"YawBrTAzp"
"YawBrRDxt"
"YawBrRDyt"
"YawBrRDzt"
"YawBrRVxp"
"YawBrRVyp"
"YawBrRVzp"
"YawBrRAxp"
"YawBrRAyp"
"YawBrRAzp"
END of input file (the word "END" must appear in the first 3 columns of this last OutList line)