Reasons for symmetric results of axial force and moments and well operated ElastoDyn simulation

[JongHoon-Jeong]

Hello.
I am currently working with the example file '5MW_OC4Jckt_DLL_WTurb_WavesIrr_MGrowth' for a fixed offshore wind turbine in OpenFAST, and I have two questions regarding the results of two tasks I performed.

1. I extracted the time histories of axial forces and moments at the interface between the tower and the jacket. The axial forces at the bottom and top of the member — M1N1FMZe and M1N2FMZe — came out with the same magnitude but opposite signs (i.e., symmetric with respect to the time axis on a graph).
   The same applies to M1N1MMZe and M1N2MMZe.
   I previously read a post addressing a similar issue, which stated that although the force transmitted from the top to the bottom due to self-weight should theoretically make the axial forces and moments different, the weight is not directly used in the nodal output, so its effect is not reflected.
   In that case, how can I get the axial forces and z-axis moments at the top and bottom nodes to come out asymmetrically (i.e., not mirror images of each other)?
   The key SubDyn settings I used are as follows:
   ----------- SubDyn MultiMember Support Structure Input File ---------------------------
   OC4 'Jacket' SubStructure Input File. The grouted connection is simulated with an equivalent tubular beam of enhanced properties. RRD 10/15/2013
   -------------------------- SIMULATION CONTROL -----------------------------------------
   False Echo - Echo input data to ".SD.ech" (flag)
   "DEFAULT" SDdeltaT - Local Integration Step. If "default", the glue-code integration step will be used.
   3 IntMethod - Integration Method [1/2/3/4 = RK4/AB4/ABM4/AM2].
   True SttcSolve - Solve dynamics about static equilibrium point
   -------------------- FEA and CRAIG-BAMPTON PARAMETERS ---------------------------------
   3 FEMMod - FEM switch: element model in the FEM. [1= Euler-Bernoulli(E-B); 2=Tapered E-B (unavailable); 3= 2-node Timoshenko; 4= 2-node tapered Timoshenko (unavailable)]
   2 NDiv - Number of sub-elements per member
   8 Nmodes - Number of internal modes to retain. If Nmodes=0 --> Guyan Reduction. If Nmodes<0 --> retain all modes.
   1 JDampings - Damping Ratios for each retained mode (% of critical) If Nmodes>0, list Nmodes structural damping ratios for each retained mode (% of critical), or a single damping ratio to be applied to all retained modes. (last entered value will be used for all remaining modes).
   2 GuyanDampMod - Guyan damping {0=none, 1=Rayleigh Damping, 2=user specified 6x6 matrix}
   0.000, 0.000 RayleighDamp - Mass and stiffness proportional damping coefficients (Rayleigh Damping) [only if GuyanDampMod=1]
   6 GuyanDampSize - Guyan damping matrix (6x6) [only if GuyanDampMod=2]
   0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
   0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
   0.0000e+00 0.0000e+00 1.066100e+06 0.0000e+00 0.0000e+00 0.0000e+00
   0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
   0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
   0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
   ---------------------------- OUTPUT: SUMMARY & OUTFILE --------------------------------
   True SumPrint - Output a Summary File (flag)
   0 OutCBModes - Output Guyan and Craig-Bampton modes {0: No output, 1: JSON output}, (flag)
   0 OutFEMModes - Output first 30 FEM modes {0: No output, 1: JSON output} (flag)
   False OutCOSM - Output cosine matrices with the selected output member forces (flag)
   False OutAll - [T/F] Output all members' end forces
   2 OutSwtch - [1/2/3] Output requested channels to: 1=.SD.out; 2=.out (generated by FAST); 3=both files.
   True TabDelim - Generate a tab-delimited output in the .SD.out file
   1 OutDec - Decimation of output in the .SD.out file
   "F15.2" OutFmt - Output format for numerical results in the .SD.out file
   "A11" OutSFmt - Output format for header strings in the .SD.out file
   ------------------------- MEMBER OUTPUT LIST ------------------------------------------
   4 NMOutputs - Number of members whose forces/displacements/velocities/accelerations will be output (-) [Must be <= 99].
   MemberID NOutCnt NodeCnt ![NOutCnt=how many nodes to get output for [< 10]; NodeCnt are local ordinal numbers from the start of the member, and must be >=1 and <= NDiv+1] If NMOutputs=0 leave blank as well.
   (-) (-) (-)
   101 2 1 2 ! M1
   102 2 1 2 ! M2
   103 2 1 2 ! M3
   104 2 1 2 ! M4
   ------------------------- SDOutList: The next line(s) contains a list of output parameters that will be output in .SD.out or .out. ------
   "M1N1FMZe, M1N2FMZe" - Leg1 dynamic forces
   "M1N1MMXe, M1N1MMYe, M1N1MMZe, M1N2MMXe, M1N2MMYe, M1N2MMZe" - Leg1 dynamic moments
   "M2N1FMZe, M2N2FMZe" - Leg1 dynamic forces
   "M2N1MMXe, M2N1MMYe, M2N1MMZe, M2N2MMXe, M2N2MMYe, M2N2MMZe" - Leg1 dynamic moments
   "M3N1FMZe, M3N2FMZe" - Leg1 dynamic forces
   "M3N1MMXe, M3N1MMYe, M3N1MMZe, M3N2MMXe, M3N2MMYe, M3N2MMZe" - Leg1 dynamic moments
   "M4N1FMZe, M4N2FMZe" - Leg1 dynamic forces
   "M4N1MMXe, M4N1MMYe, M4N1MMZe, M4N2MMXe, M4N2MMYe, M4N2MMZe" - Leg1 dynamic moments
   END of output channels and end of file. (the word "END" must appear in the first 3 columns of this line)

2. For this task, I tried to extract time histories of axial forces and moments at the top, middle, and bottom of the tower, and set the initial conditions in ElastoDyn accordingly. I ran the simulation multiple times with different settings, and what I found surprising is that the simulation runs fine whether I use setting (1) or setting (2) below.
   Normally, to minimize startup transients that would arise from applying a large amount of simulation loading, and to ensure the controller operates from the correct initial values, one should use the values recommended in the NREL specification report for the ElastoDyn initial conditions.

(1)
---------------------- INITIAL CONDITIONS --------------------------------------
0 OoPDefl - Initial out-of-plane blade-tip displacement (meters)
0 IPDefl - Initial in-plane blade-tip deflection (meters)
0 BlPitch(1) - Blade 1 initial pitch (degrees)
0 BlPitch(2) - Blade 2 initial pitch (degrees)
0 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)
12.1 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)
-0.00702 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)

(2)
---------------------- INITIAL CONDITIONS --------------------------------------
4.5 OoPDefl - Initial out-of-plane blade-tip displacement (meters)
-0.75 IPDefl - Initial in-plane blade-tip deflection (meters)
3.75 BlPitch(1) - Blade 1 initial pitch (degrees)
3.75 BlPitch(2) - Blade 2 initial pitch (degrees)
3.75 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)
12.1 RotSpeed - Initial or fixed rotor speed (rpm)
0 NacYaw - Initial or fixed nacelle-yaw angle (degrees)
0.33 TTDspFA - Initial fore-aft tower-top displacement (meters)
-0.05 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)
-0.00702 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)

Output parameters requested:
---------------------- OUTPUT --------------------------------------------------
True SumPrint - Print summary data to ".sum" (flag)
2 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)
"F15.2" OutFmt - Format used for text tabular output (except time). Resulting field should be 10 characters. (quoted string) (currently unused)
30 TStart - Time to begin tabular output (s) (currently unused)
1 DecFact - Decimation factor for tabular output {1: output every time step} (-) (currently unused)
3 NTwGages - Number of tower nodes that have strain gages for output [0 to 9] (-)
1, 10, 20 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] (-)
0 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, (-)
"TwHt1FLzt" - Local tower yaw (or torsional) force of tower gage 1
"TwHt1MLxt" - Local tower roll (or side-to-side) moment of tower gage 1
"TwHt1MLyt" - Local tower pitching (or fore-aft) moment of tower gage 1
"TwHt1MLzt" - Local tower yaw (or torsional) moment of tower gage 1
"TwHt2FLzt" - Local tower yaw (or torsional) force of tower gage 2
"TwHt2MLxt" - Local tower roll (or side-to-side) moment of tower gage 2
"TwHt2MLyt" - Local tower pitching (or fore-aft) moment of tower gage 2
"TwHt2MLzt" - Local tower yaw (or torsional) moment of tower gage 2
"TwHt3FLzt" - Local tower yaw (or torsional) force of tower gage 3
"TwHt3MLxt" - Local tower roll (or side-to-side) moment of tower gage 3
"TwHt3MLyt" - Local tower pitching (or fore-aft) moment of tower gage 3
"TwHt3MLzt" - Local tower yaw (or torsional) moment of tower gage 3
END of OutList section (the word "END" must appear in the first 3 columns of the last OutList line)

[jjonkman]

Dear @JongHoon-Jeong,

Regarding (1), the sign change between the loads output at either end of a given element in SubDyn has been discussed in the following OpenFAST issue: #2781 and in the online SubDyn documentation on readthedocs: https://openfast.readthedocs.io/en/main/source/user/subdyn/theory.html#nodal-loads-calculation. The way SubDyn handles self weight and its implication on nodal load outputs has also been discussed in the following OpenFAST issue: #2325, along with a suggested workaround to improve the results.

Regarding (2), when you say the "simulation runs fine", I assume you mean that both simulations are numerical stable, although the start-up transients differ. I would expect the use of initial conditions closer to the steady-state solution for a given set of conditions will have less start-up transients; is that what you are seeing? Using initial conditions that are far way from the steady-state solution will result in longer start-up transients, and may become unstable if, e.g., the controller gets confused by the state of the turbine and produces unreliable output.

Best regards,

[JongHoon-Jeong]

Dear Dr. Jonkman,
Thank you so much for your kind and detailed response.
(1) Based on your advice, I changed NDiv multiple times (3, 4, 6, etc.) and re-ran the simulation with the settings shown below. However, I still get results where M1N1FMZe = -M1N2FMZe and M1N1MMZe = -M1N2MMZe.
4 NDiv - Number of sub-elements per member
32 Nmodes - Number of internal modes to retain. If Nmodes=0 --> Guyan Reduction. If Nmodes<0 --> retain all modes.

---------------------------- OUTPUT: SUMMARY & OUTFILE --------------------------------
True SumPrint - Output a Summary File (flag)
0 OutCBModes - Output Guyan and Craig-Bampton modes {0: No output, 1: JSON output}, (flag)
0 OutFEMModes - Output first 30 FEM modes {0: No output, 1: JSON output} (flag)
False OutCOSM - Output cosine matrices with the selected output member forces (flag)
False OutAll - [T/F] Output all members' end forces
2 OutSwtch - [1/2/3] Output requested channels to: 1=.SD.out; 2=.out (generated by FAST); 3=both files.
True TabDelim - Generate a tab-delimited output in the .SD.out file
1 OutDec - Decimation of output in the .SD.out file
"F15.2" OutFmt - Output format for numerical results in the .SD.out file
"A11" OutSFmt - Output format for header strings in the .SD.out file
------------------------- MEMBER OUTPUT LIST ------------------------------------------
4 NMOutputs - Number of members whose forces/displacements/velocities/accelerations will be output (-) [Must be <= 99].
MemberID NOutCnt NodeCnt ![NOutCnt=how many nodes to get output for [< 10]; NodeCnt are local ordinal numbers from the start of the member, and must be >=1 and <= NDiv+1] If NMOutputs=0 leave blank as well.
(-) (-) (-)
101 2 1 5 ! M1
102 2 1 5 ! M2
103 2 1 5 ! M3
104 2 1 5 ! M4
In addition, the following warnings also appear:
Running SubDyn.
Fixed bottom case detected
Guyan extra moment will be included in loads (fixed-bottom case detected)
Performing Craig-Bampton reduction 2400 DOFs -> 32 modes + 48 DOFs
[WARN] Complex eigenvalue found with small Im compare to Re
[WARN] Complex eigenvalue found with small Im compare to Re
[WARN] Complex eigenvalue found with small Im compare to Re
[WARN] Complex eigenvalue found with small Im compare to Re
[WARN] Complex eigenvalue found with small Im compare to Re
[WARN] Complex eigenvalue found with small Im compare to Re
Could you please advise on how to eliminate these warnings, and how to prevent the axial force and z-axis moment outputs at the top and bottom of the member from having equal magnitudes with opposite signs?

(2) When comparing the case where initial conditions close to the steady-state solution are applied versus the case where initial conditions far from the steady-state solution are applied, the time required for the startup transient to settle is similar in both cases. While the Total Real Time is slightly shorter when using initial conditions closer to the steady-state solution (by approximately 0.01 hours), it is puzzling that both cases run successfully without significant differences.

Thank you for your time and assistance.

[JongHoon-Jeong]

I give you ElastoDyn, SubDyn, fst with txt file, too.
5MW_OC4Jckt_DLL_WTurb_WavesIrr_MGrowth_fst.txt
ElastoDyn.txt
SubDyn.txt

[jjonkman]

Dear @JongHoon-Jeong,

Regarding (1), I would expect increasing NDiv would change how self-weight impacts the nodal loads at the ends of a member, Are the results exactly unchanged between your NDiv = 2 and NDiv = 4 cases? Perhaps the self weight is small for the members you are considering relative to other loads in the system?

Regarding (2), can you quantitative results of what you are seeing, e.g., time series during the start-up transient?

Best regards,

[JongHoon-Jeong]

Thank you so much for your continued responses despite your busy schedule. However, the issue has not yet been resolved, and I would like to ask one final question regarding this matter.
With a simulation time of 3600 seconds, the axial force and z-axis moment of Member 1 were compared between the case of NDiv = 2 and the case of NDiv = 4, as shown in the table below.

To run the simulations, DT and DT_Out were set to 0.005 for NDiv = 2, and 0.002 for NDiv = 4. The results are presented in a table at 1-second intervals from 0 to 10 seconds.
Although the two cases yield different results, and the values are presented to four decimal places, the magnitudes at the top and bottom of the member are still equal with opposite signs.
(2) I apologize, but I am not sure how long the startup transient lasts. Based on my own judgment, I extracted the time histories of RotSpeed, TTDspFA, and OoPDefl1 for both cases in order to estimate the time required for these responses to stabilize, and plotted each history using MATLAB.
The plots for both cases are shown below.


To be honest, I am not sure at what point the startup transient ends, so I have been unable to extract the response history during the startup transient period. Based on the figures above, up to what point would the startup transient last? Also, due to schedule constraints, I was unable to run long simulations, so I set NDiv = 1 in SubDyn and DT and DT_Out to 0.01. Would this setting also affect the output values from ElastoDyn?

[jjonkman]

Dear @JongHoon-Jeong,

To @RBergua's point, does the solution of (1) change if you reduce Nmodes back down to 8, which is how the original r-test model is defined (being curious if increasing the number of modes is yielding unexpected behavior).

Best regards,

[JongHoon-Jeong]

1. The settings were modified as described below, and the results for NDiv = 2 and NDiv = 4 are presented in the table below. However, in both cases, the responses at the top and bottom of the member are still equal in magnitude with opposite signs.

(1) SubDyn settings for NDiv = 2
----------- SubDyn MultiMember Support Structure Input File ---------------------------
OC4 'Jacket' SubStructure Input File. The grouted connection is simulated with an equivalent tubular beam of enhanced properties. RRD 10/15/2013
-------------------------- SIMULATION CONTROL -----------------------------------------
False Echo - Echo input data to ".SD.ech" (flag)
"DEFAULT" SDdeltaT - Local Integration Step. If "default", the glue-code integration step will be used.
3 IntMethod - Integration Method [1/2/3/4 = RK4/AB4/ABM4/AM2].
True SttcSolve - Solve dynamics about static equilibrium point
-------------------- FEA and CRAIG-BAMPTON PARAMETERS ---------------------------------
3 FEMMod - FEM switch: element model in the FEM. [1= Euler-Bernoulli(E-B); 2=Tapered E-B (unavailable); 3= 2-node Timoshenko; 4= 2-node tapered Timoshenko (unavailable)]
2 NDiv - Number of sub-elements per member
8 Nmodes - Number of internal modes to retain. If Nmodes=0 --> Guyan Reduction. If Nmodes<0 --> retain all modes.
1 JDampings - Damping Ratios for each retained mode (% of critical) If Nmodes>0, list Nmodes structural damping ratios for each retained mode (% of critical), or a single damping ratio to be applied to all retained modes. (last entered value will be used for all remaining modes).
1 GuyanDampMod - Guyan damping {0=none, 1=Rayleigh Damping, 2=user specified 6x6 matrix}
0.000, 0.001 RayleighDamp - Mass and stiffness proportional damping coefficients (Rayleigh Damping) [only if GuyanDampMod=1]
6 GuyanDampSize - Guyan damping matrix (6x6) [only if GuyanDampMod=2]
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 1.066100e+06 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
---- STRUCTURE JOINTS: joints connect structure members (~Hydrodyn Input File) --------
64 NJoints - Number of joints (-)
JointID JointXss JointYss JointZss JointType JointDirX JointDirY JointDirZ JointStiff ![Coordinates of Member joints in SS-Coordinate System][JointType={1:cantilever, 2:universal joint, 3:revolute joint, 4:spherical joint}]
(-) (m) (m) (m) (-) (-) (-) (-) (Nm/rad)
1 6.00000 6.00000 -45.50000 1 0.0 0.0 0.0 0.0
2 6.00000 6.00000 -45.00000 1 0.0 0.0 0.0 0.0
3 5.96700 5.96700 -44.00100 1 0.0 0.0 0.0 0.0
4 5.93900 5.93900 -43.12700 1 0.0 0.0 0.0 0.0
5 5.33300 5.33300 -24.61400 1 0.0 0.0 0.0 0.0
6 -6.00000 6.00000 -45.50000 1 0.0 0.0 0.0 0.0
7 -6.00000 6.00000 -45.00000 1 0.0 0.0 0.0 0.0
8 -5.96700 5.96700 -44.00100 1 0.0 0.0 0.0 0.0
9 -5.93900 5.93900 -43.12700 1 0.0 0.0 0.0 0.0
10 -5.33300 5.33300 -24.61400 1 0.0 0.0 0.0 0.0
11 -6.00000 -6.00000 -45.50000 1 0.0 0.0 0.0 0.0
12 -6.00000 -6.00000 -45.00000 1 0.0 0.0 0.0 0.0
13 -5.96700 -5.96700 -44.00100 1 0.0 0.0 0.0 0.0
14 -5.93900 -5.93900 -43.12700 1 0.0 0.0 0.0 0.0
15 -5.33300 -5.33300 -24.61400 1 0.0 0.0 0.0 0.0
16 6.00000 -6.00000 -45.50000 1 0.0 0.0 0.0 0.0
17 6.00000 -6.00000 -45.00000 1 0.0 0.0 0.0 0.0
18 5.96700 -5.96700 -44.00100 1 0.0 0.0 0.0 0.0
19 5.93900 -5.93900 -43.12700 1 0.0 0.0 0.0 0.0
20 5.33300 -5.33300 -24.61400 1 0.0 0.0 0.0 0.0
21 4.82000 4.82000 -8.92200 1 0.0 0.0 0.0 0.0
22 4.38500 4.38500 4.37800 1 0.0 0.0 0.0 0.0
23 4.01600 4.01600 15.65100 1 0.0 0.0 0.0 0.0
24 4.00000 4.00000 16.15000 1 0.0 0.0 0.0 0.0
25 -4.82000 4.82000 -8.92200 1 0.0 0.0 0.0 0.0
26 -4.38500 4.38500 4.37800 1 0.0 0.0 0.0 0.0
27 -4.01600 4.01600 15.65100 1 0.0 0.0 0.0 0.0
28 -4.00000 4.00000 16.15000 1 0.0 0.0 0.0 0.0
29 -4.82000 -4.82000 -8.92200 1 0.0 0.0 0.0 0.0
30 -4.38500 -4.38500 4.37800 1 0.0 0.0 0.0 0.0
31 -4.01600 -4.01600 15.65100 1 0.0 0.0 0.0 0.0
32 -4.00000 -4.00000 16.15000 1 0.0 0.0 0.0 0.0
33 4.82000 -4.82000 -8.92200 1 0.0 0.0 0.0 0.0
34 4.38500 -4.38500 4.37800 1 0.0 0.0 0.0 0.0
35 4.01600 -4.01600 15.65100 1 0.0 0.0 0.0 0.0
36 4.00000 -4.00000 16.15000 1 0.0 0.0 0.0 0.0
37 5.62000 0.00000 -33.37300 1 0.0 0.0 0.0 0.0
38 -5.62000 0.00000 -33.37300 1 0.0 0.0 0.0 0.0
39 0.00000 5.62000 -33.37300 1 0.0 0.0 0.0 0.0
40 0.00000 -5.62000 -33.37300 1 0.0 0.0 0.0 0.0
41 5.06400 0.00000 -16.37100 1 0.0 0.0 0.0 0.0
42 -5.06400 0.00000 -16.37100 1 0.0 0.0 0.0 0.0
43 0.00000 5.06400 -16.37100 1 0.0 0.0 0.0 0.0
44 0.00000 -5.06400 -16.37100 1 0.0 0.0 0.0 0.0
45 4.59200 0.00000 -1.95800 1 0.0 0.0 0.0 0.0
46 -4.59200 0.00000 -1.95800 1 0.0 0.0 0.0 0.0
47 0.00000 4.59200 -1.95800 1 0.0 0.0 0.0 0.0
48 0.00000 -4.59200 -1.95800 1 0.0 0.0 0.0 0.0
49 4.19300 0.00000 10.26200 1 0.0 0.0 0.0 0.0
50 -4.19300 0.00000 10.26200 1 0.0 0.0 0.0 0.0
51 0.00000 4.19300 10.26200 1 0.0 0.0 0.0 0.0
52 0.00000 -4.19300 10.26200 1 0.0 0.0 0.0 0.0
53 4.00000 4.00000 20.15000 1 0.0 0.0 0.0 0.0
54 -4.00000 4.00000 20.15000 1 0.0 0.0 0.0 0.0
55 4.00000 -4.00000 20.15000 1 0.0 0.0 0.0 0.0
56 -4.00000 -4.00000 20.15000 1 0.0 0.0 0.0 0.0
57 6.00000 -6.00000 -49.50000 1 0.0 0.0 0.0 0.0
58 6.00000 6.00000 -49.50000 1 0.0 0.0 0.0 0.0
59 -6.00000 -6.00000 -49.50000 1 0.0 0.0 0.0 0.0
60 -6.00000 6.00000 -49.50000 1 0.0 0.0 0.0 0.0
61 6.00000 -6.00000 -50.00100 1 0.0 0.0 0.0 0.0
62 6.00000 6.00000 -50.00100 1 0.0 0.0 0.0 0.0
63 -6.00000 -6.00000 -50.00100 1 0.0 0.0 0.0 0.0
64 -6.00000 6.00000 -50.00100 1 0.0 0.0 0.0 0.0
------------------- BASE REACTION JOINTS: 1/0 for Locked/Free DOF @ each Reaction Node ---------------------
4 NReact - Number of Joints with reaction forces; be sure to remove all rigid motion DOFs of the structure (else det([K])=[0])
RJointID RctTDXss RctTDYss RctTDZss RctRDXss RctRDYss RctRDZss SSIfile ![Global Coordinate System]
(-) (flag) (flag) (flag) (flag) (flag) (flag) (string)
61 1 1 1 1 1 1 ""
62 1 1 1 1 1 1 ""
63 1 1 1 1 1 1 ""
64 1 1 1 1 1 1 ""
------- INTERFACE JOINTS: 1/0 for Locked (to the TP)/Free DOF @each Interface Joint (only Locked-to-TP implemented thus far (=rigid TP)) ---------
8 NInterf - Number of interface joints locked to the Transition Piece (TP): be sure to remove all rigid motion dofs
IJointID ItfTDXss ItfTDYss ItfTDZss ItfRDXss ItfRDYss ItfRDZss
(-) (flag) (flag) (flag) (flag) (flag) (flag)
24 1 1 1 1 1 1
28 1 1 1 1 1 1
32 1 1 1 1 1 1
36 1 1 1 1 1 1
53 1 1 1 1 1 1
54 1 1 1 1 1 1
55 1 1 1 1 1 1
56 1 1 1 1 1 1
----------------------------------- MEMBERS -------------------------------------------
112 NMembers - Number of members (-)
MemberID MJointID1 MJointID2 MPropSetID1 MPropSetID2 MType MSpin/COSMID ! [MType={1c:beam circ., 1r:beam rect., 2:cable, 3:rigid, 4:beam arb., 5:spring}. COMSID={-1:none}]
(-) (-) (-) (-) (-) (-) (deg/-)
1 1 2 2 2 1c 0
2 2 3 2 2 1c 0
3 3 4 2 2 1c 0
4 4 5 2 2 1c 0
5 6 7 2 2 1c 0
6 7 8 2 2 1c 0
7 8 9 2 2 1c 0
8 9 10 2 2 1c 0
9 11 12 2 2 1c 0
10 12 13 2 2 1c 0
11 13 14 2 2 1c 0
12 14 15 2 2 1c 0
13 16 17 2 2 1c 0
14 17 18 2 2 1c 0
15 18 19 2 2 1c 0
16 19 20 2 2 1c 0
17 5 21 3 3 1c 0
18 21 22 3 3 1c 0
19 22 23 3 3 1c 0
20 23 24 3 3 1c 0
21 10 25 3 3 1c 0
22 25 26 3 3 1c 0
23 26 27 3 3 1c 0
24 27 28 3 3 1c 0
25 15 29 3 3 1c 0
26 29 30 3 3 1c 0
27 30 31 3 3 1c 0
28 31 32 3 3 1c 0
29 20 33 3 3 1c 0
30 33 34 3 3 1c 0
31 34 35 3 3 1c 0
32 35 36 3 3 1c 0
33 8 3 1 1 1c 0
34 13 8 1 1 1c 0
35 13 18 1 1 1c 0
36 18 3 1 1 1c 0
37 4 37 1 1 1c 0
38 37 20 1 1 1c 0
39 19 37 1 1 1c 0
40 37 5 1 1 1c 0
41 9 38 1 1 1c 0
42 38 15 1 1 1c 0
43 14 38 1 1 1c 0
44 38 10 1 1 1c 0
45 4 39 1 1 1c 0
46 39 10 1 1 1c 0
47 9 39 1 1 1c 0
48 39 5 1 1 1c 0
49 19 40 1 1 1c 0
50 40 15 1 1 1c 0
51 14 40 1 1 1c 0
52 40 20 1 1 1c 0
53 5 41 1 1 1c 0
54 41 33 1 1 1c 0
55 20 41 1 1 1c 0
56 41 21 1 1 1c 0
57 10 42 1 1 1c 0
58 42 29 1 1 1c 0
59 15 42 1 1 1c 0
60 42 25 1 1 1c 0
61 5 43 1 1 1c 0
62 43 25 1 1 1c 0
63 10 43 1 1 1c 0
64 43 21 1 1 1c 0
65 20 44 1 1 1c 0
66 44 29 1 1 1c 0
67 15 44 1 1 1c 0
68 44 33 1 1 1c 0
69 21 45 1 1 1c 0
70 45 34 1 1 1c 0
71 33 45 1 1 1c 0
72 45 22 1 1 1c 0
73 25 46 1 1 1c 0
74 46 30 1 1 1c 0
75 29 46 1 1 1c 0
76 46 26 1 1 1c 0
77 21 47 1 1 1c 0
78 47 26 1 1 1c 0
79 25 47 1 1 1c 0
80 47 22 1 1 1c 0
81 33 48 1 1 1c 0
82 48 30 1 1 1c 0
83 29 48 1 1 1c 0
84 48 34 1 1 1c 0
85 22 49 1 1 1c 0
86 49 35 1 1 1c 0
87 34 49 1 1 1c 0
88 49 23 1 1 1c 0
89 26 50 1 1 1c 0
90 50 31 1 1 1c 0
91 30 50 1 1 1c 0
92 50 27 1 1 1c 0
93 22 51 1 1 1c 0
94 51 27 1 1 1c 0
95 26 51 1 1 1c 0
96 51 23 1 1 1c 0
97 34 52 1 1 1c 0
98 52 31 1 1 1c 0
99 30 52 1 1 1c 0
100 52 35 1 1 1c 0
101 24 53 4 4 1c 0
102 28 54 4 4 1c 0
103 32 56 4 4 1c 0
104 36 55 4 4 1c 0
105 58 1 5 5 1c 0
106 57 16 5 5 1c 0
107 60 6 5 5 1c 0
108 59 11 5 5 1c 0
109 62 58 6 6 1c 0
110 61 57 6 6 1c 0
111 64 60 6 6 1c 0
112 63 59 6 6 1c 0
------------------ CIRCULAR BEAM CROSS-SECTION PROPERTIES -----------------------------
6 NPropSets - Number of structurally unique cross-sections
PropSetID YoungE ShearG MatDens XsecD XsecT
(-) (N/m2) (N/m2) (kg/m3) (m) (m)
1 2.10000e+11 8.07690e+10 7850.00 0.800000 0.020000
2 2.10000e+11 8.07690e+10 7850.00 1.200000 0.050000
3 2.10000e+11 8.07690e+10 7850.00 1.200000 0.035000
4 2.10000e+11 8.07690e+10 7850.00 1.200000 0.040000
5 2.10000e+11 8.07690e+10 3339.12 2.082000 0.491000
6 2.10000e+11 8.07690e+10 7850.00 2.082000 0.060000
----------------- RECTANGULAR BEAM CROSS-SECTION PROPERTIES ---------------------------
0 NPropSets - Number of structurally unique cross-sections (if 0 the following table is ignored)
PropSetID YoungE ShearG MatDens XsecA XsecB XsecT
(-) (N/m2) (N/m2) (kg/m3) (m) (m) (m)
----------------- ARBITRARY BEAM CROSS-SECTION PROPERTIES -----------------------------
0 NXPropSets - Number of structurally unique non-circular cross-sections (if 0 the following table is ignored)
PropSetID YoungE ShearG MatDens XsecA XsecAsx XsecAsy XsecJxx XsecJyy XsecJ0 XsecJt
(-) (N/m2) (N/m2) (kg/m3) (m2) (m2) (m2) (m4) (m4) (m4) (m4)
-------------------------- CABLE PROPERTIES -------------------------------------------
0 NCablePropSets - Number of cable cable properties
PropSetID EA MatDens T0 CtrlChannel
(-) (N) (kg/m) (N) (-)
----------------------- RIGID LINK PROPERTIES -----------------------------------------
0 NRigidPropSets - Number of rigid link properties
PropSetID MatDens
(-) (kg/m)
----------------------- SPRING ELEMENT PROPERTIES -------------------------------------
0 NSpringPropSets - Number of spring properties
PropSetID k11 k12 k13 k14 k15 k16 k22 k23 k24 k25 k26 k33 k34 k35 k36 k44 k45 k46 k55 k56 k66
(-) (N/m) (N/m) (N/m) (N/rad) (N/rad) (N/rad) (N/m) (N/m) (N/rad) (N/rad) (N/rad) (N/m) (N/rad) (N/rad) (N/rad) (Nm/rad) (Nm/rad) (Nm/rad) (Nm/rad) (Nm/rad) (Nm/rad)
---------------------- MEMBER COSINE MATRICES COSM(i,j) -------------------------------
0 NCOSMs - Number of unique cosine matrices (i.e., of unique member alignments including principal axis rotations); ignored if NXPropSets=0 or 9999 in any element below
COSMID COSM11 COSM12 COSM13 COSM21 COSM22 COSM23 COSM31 COSM32 COSM33
(-) (-) (-) (-) (-) (-) (-) (-) (-) (-)
------------------------ JOINT ADDITIONAL CONCENTRATED MASSES--------------------------
0 NCmass - Number of joints with concentrated masses; Global Coordinate System
CMJointID JMass JMXX JMYY JMZZ JMXY JMXZ JMYZ MCGX MCGY MCGZ
(-) (kg) (kgm^2) (kgm^2) (kgm^2) (kgm^2) (kgm^2) (kgm^2) (m) (m) (m)
---------------------------- OUTPUT: SUMMARY & OUTFILE --------------------------------
True SumPrint - Output a Summary File (flag)
1 OutCBModes - Output Guyan and Craig-Bampton modes {0: No output, 1: JSON output}, (flag)
0 OutFEMModes - Output first 30 FEM modes {0: No output, 1: JSON output} (flag)
False OutCOSM - Output cosine matrices with the selected output member forces (flag)
False OutAll - [T/F] Output all members' end forces
2 OutSwtch - [1/2/3] Output requested channels to: 1=.SD.out; 2=.out (generated by FAST); 3=both files.
True TabDelim - Generate a tab-delimited output in the .SD.out file
1 OutDec - Decimation of output in the .SD.out file
"F10.4" OutFmt - Output format for numerical results in the .SD.out file
"A11" OutSFmt - Output format for header strings in the .SD.out file
------------------------- MEMBER OUTPUT LIST ------------------------------------------
4 NMOutputs - Number of members whose forces/displacements/velocities/accelerations will be output (-) [Must be <= 99].
MemberID NOutCnt NodeCnt ![NOutCnt=how many nodes to get output for [< 10]; NodeCnt are local ordinal numbers from the start of the member, and must be >=1 and <= NDiv+1] If NMOutputs=0 leave blank as well.
(-) (-) (-)
101 2 1 3 ! M1
102 2 1 3 ! M2
103 2 1 3 ! M3
104 2 1 3 ! M4
------------------------- SDOutList: The next line(s) contains a list of output parameters that will be output in .SD.out or .out. ------
"M1N1FMZe, M1N2FMZe" - Leg1 dynamic forces
"M1N1MMXe, M1N1MMYe, M1N1MMZe, M1N2MMXe, M1N2MMYe, M1N2MMZe" - Leg1 dynamic moments
"M2N1FMZe, M2N2FMZe" - Leg1 dynamic forces
"M2N1MMXe, M2N1MMYe, M2N1MMZe, M2N2MMXe, M2N2MMYe, M2N2MMZe" - Leg1 dynamic moments
"M3N1FMZe, M3N2FMZe" - Leg1 dynamic forces
"M3N1MMXe, M3N1MMYe, M3N1MMZe, M3N2MMXe, M3N2MMYe, M3N2MMZe" - Leg1 dynamic moments
"M4N1FMZe, M4N2FMZe" - Leg1 dynamic forces
"M4N1MMXe, M4N1MMYe, M4N1MMZe, M4N2MMXe, M4N2MMYe, M4N2MMZe" - Leg1 dynamic moments
END of output channels and end of file. (the word "END" must appear in the first 3 columns of this line)

(2) SubDyn settings for NDiv = 4
-------------------- FEA and CRAIG-BAMPTON PARAMETERS ---------------------------------
3 FEMMod - FEM switch: element model in the FEM. [1= Euler-Bernoulli(E-B); 2=Tapered E-B (unavailable); 3= 2-node Timoshenko; 4= 2-node tapered Timoshenko (unavailable)]
4 NDiv - Number of sub-elements per member
8 Nmodes - Number of internal modes to retain. If Nmodes=0 --> Guyan Reduction. If Nmodes<0 --> retain all modes.
1 JDampings - Damping Ratios for each retained mode (% of critical) If Nmodes>0, list Nmodes structural damping ratios for each retained mode (% of critical), or a single damping ratio to be applied to all retained modes. (last entered value will be used for all remaining modes).
1 GuyanDampMod - Guyan damping {0=none, 1=Rayleigh Damping, 2=user specified 6x6 matrix}
0.000, 0.001 RayleighDamp - Mass and stiffness proportional damping coefficients (Rayleigh Damping) [only if GuyanDampMod=1]
6 GuyanDampSize - Guyan damping matrix (6x6) [only if GuyanDampMod=2]
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 1.066100e+06 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00
0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00 0.0000e+00

------------------------- MEMBER OUTPUT LIST ------------------------------------------
4 NMOutputs - Number of members whose forces/displacements/velocities/accelerations will be output (-) [Must be <= 99].
MemberID NOutCnt NodeCnt ![NOutCnt=how many nodes to get output for [< 10]; NodeCnt are local ordinal numbers from the start of the member, and must be >=1 and <= NDiv+1] If NMOutputs=0 leave blank as well.
(-) (-) (-)
101 2 1 5 ! M1
102 2 1 5 ! M2
103 2 1 5 ! M3
104 2 1 5 ! M4
------------------------- SDOutList: The next line(s) contains a list of output parameters that will be output in .SD.out or .out. ------
"M1N1FMZe, M1N2FMZe" - Leg1 dynamic forces
"M1N1MMXe, M1N1MMYe, M1N1MMZe, M1N2MMXe, M1N2MMYe, M1N2MMZe" - Leg1 dynamic moments
"M2N1FMZe, M2N2FMZe" - Leg1 dynamic forces
"M2N1MMXe, M2N1MMYe, M2N1MMZe, M2N2MMXe, M2N2MMYe, M2N2MMZe" - Leg1 dynamic moments
"M3N1FMZe, M3N2FMZe" - Leg1 dynamic forces
"M3N1MMXe, M3N1MMYe, M3N1MMZe, M3N2MMXe, M3N2MMYe, M3N2MMZe" - Leg1 dynamic moments
"M4N1FMZe, M4N2FMZe" - Leg1 dynamic forces
"M4N1MMXe, M4N1MMYe, M4N1MMZe, M4N2MMXe, M4N2MMYe, M4N2MMZe" - Leg1 dynamic moments

Note that only a portion of the settings are shown here; the remaining parameters are configured with the same values as in (1).

2. Following your advice, RBergua, I set Nmodes back to 8, and the warning '[WARN] Complex eigenvalue found with small Im compare to Re' no longer appears. Thank you.
   In addition, I obtained the JSON file and used it to animate the modes for both cases. Snapshots of the maximum displacement for each mode are shown below. Note that the SubDyn output parameters shown in Section 1 were disabled for this part.

For these simulations, WindType = 1 and WaveMod = 0 were applied, and the ElastoDyn settings are presented below.

• Case 1
  ------- ELASTODYN for OpenFAST INPUT FILE -------------------------------------------
  OC4 TOWER+ 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 ".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]
  True DrTrDOF - Drivetrain rotational-flexibility DOF (flag)
  True GenDOF - Generator DOF (flag)
  True 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 --------------------------------------
  4.5 OoPDefl - Initial out-of-plane blade-tip displacement (meters)
  -0.75 IPDefl - Initial in-plane blade-tip deflection (meters)
  3.75 BlPitch(1) - Blade 1 initial pitch (degrees)
  3.75 BlPitch(2) - Blade 2 initial pitch (degrees)
  3.75 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)
  12.1 RotSpeed - Initial or fixed rotor speed (rpm)
  0 NacYaw - Initial or fixed nacelle-yaw angle (degrees)
  0.33 TTDspFA - Initial fore-aft tower-top displacement (meters)
  -0.00702 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)
  -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)
  -5.0191 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 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)
  1.96256 Twr2Shft - Vertical distance from the tower-top to the rotor shaft (meters)
  88.15 TowerHt - Height of tower relative to ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] (meters)
  20.15 TowerBsHt - Height of tower base relative to ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] (meters)
  0 PtfmCMxt - Downwind distance from the ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] to the platform CM (meters)
  0 PtfmCMyt - Lateral distance from the ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] to the platform CM (meters)
  18.15 PtfmCMzt - Vertical distance from the ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] to the platform CM (meters)
  18.15 PtfmRefzt - Vertical distance from the ground level [onshore], MSL [offshore wind or floating MHK], or seabed [fixed MHK] 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)
  2607890 NacYIner - Nacelle inertia about yaw axis (kg m^2)
  0 YawBrMass - Yaw bearing mass (kg)
  666000 PtfmMass - Platform mass (kg)
  6002880 PtfmRIner - Platform inertia for roll tilt rotation about the platform CM (kg m^2)
  6002880 PtfmPIner - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)
  10229800 PtfmYIner - Platform inertia for yaw rotation about the platform CM (kg m^2)
  0 PtfmXYIner - Platform xy moment of inertia about the platform CM (=-int(xydm)) (kg m^2)
  0 PtfmYZIner - Platform yz moment of inertia about the platform CM (=-int(yzdm)) (kg m^2)
  0 PtfmXZIner - Platform xz moment of inertia about the platform CM (=-int(xzdm)) (kg m^2)
  ---------------------- BLADE ---------------------------------------------------
  17 BldNodes - Number of blade nodes (per blade) used for analysis (-)
  "../5MW_Baseline/NRELOffshrBsline5MW_Blade.dat" BldFile(1) - Name of file containing properties for blade 1 (quoted string)
  "../5MW_Baseline/NRELOffshrBsline5MW_Blade.dat" BldFile(2) - Name of file containing properties for blade 2 (quoted string)
  "../5MW_Baseline/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]
  ---------------------- YAW-FRICTION --------------------------------------------
  0 YawFrctMod - Yaw-friction model {0: none, 1: friction independent of yaw-bearing force and bending moment, 2: friction with Coulomb terms depending on yaw-bearing force and bending moment, 3: user defined model} (switch)
  300 M_CSmax - Maximum static Coulomb friction torque (N-m) [M_CSmax when YawFrctMod=1; |Fz|*M_CSmax when YawFrctMod=2 and Fz<0]
  0 M_FCSmax - Maximum static Coulomb friction torque proportional to yaw bearing shear force (N-m) [sqrt(Fx^2+Fy^2)*M_FCSmax; only used when YawFrctMod=2]
  0 M_MCSmax - Maximum static Coulomb friction torque proportional to yaw bearing bending moment (N-m) [sqrt(Mx^2+My^2)*M_MCSmax; only used when YawFrctMod=2]
  40 M_CD - Dynamic Coulomb friction moment (N-m) [M_CD when YawFrctMod=1; |Fz|*M_CD when YawFrctMod=2 and Fz<0]
  0 M_FCD - Dynamic Coulomb friction moment proportional to yaw bearing shear force (N-m) [sqrt(Fx^2+Fy^2)*M_FCD; only used when YawFrctMod=2]
  0 M_MCD - Dynamic Coulomb friction moment proportional to yaw bearing bending moment (N-m) [sqrt(Mx^2+My^2)*M_MCD; only used when YawFrctMod=2]
  0 sig_v - Linear viscous friction coefficient (N-m/(rad/s))
  0 sig_v2 - Quadratic viscous friction coefficient (N-m/(rad/s)^2)
  0 OmgCut - Yaw angular velocity cutoff below which viscous friction is linearized (rad/s)
  ---------------------- DRIVETRAIN ----------------------------------------------
  100 GBoxEff - Gearbox efficiency (%)
  97 GBRatio - Gearbox ratio (-)
  867637000 DTTorSpr - Drivetrain torsional spring (N-m/rad)
  6215000 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_OC4Jacket_ElastoDyn_Tower.dat" TwrFile - Name of file containing tower properties (quoted string)
  ---------------------- OUTPUT --------------------------------------------------
  True SumPrint - Print summary data to ".sum" (flag)
  2 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)
  "F10.5" OutFmt - Format used for text tabular output (except time). Resulting field should be 10 characters. (quoted string) (currently unused)
  30 TStart - Time to begin tabular output (s) (currently unused)
  1 DecFact - Decimation factor for tabular output {1: output every time step} (-) (currently unused)
  3 NTwGages - Number of tower nodes that have strain gages for output [0 to 9] (-)
  1, 10, 20 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] (-)
  0 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
  "RotSpeed" - Low-speed shaft and high-speed shaft speeds
  "TTDspFA" - Tower fore-aft and side-to-side displacements and top twist
  "TwHt1FLzt" - Local tower yaw (or torsional) force of tower gage 1
  "TwHt1MLxt" - Local tower roll (or side-to-side) moment of tower gage 1
  "TwHt1MLyt" - Local tower pitching (or fore-aft) moment of tower gage 1
  "TwHt1MLzt" - Local tower yaw (or torsional) moment of tower gage 1
  "TwHt2FLzt" - Local tower yaw (or torsional) force of tower gage 2
  "TwHt2MLxt" - Local tower roll (or side-to-side) moment of tower gage 2
  "TwHt2MLyt" - Local tower pitching (or fore-aft) moment of tower gage 2
  "TwHt2MLzt" - Local tower yaw (or torsional) moment of tower gage 2
  "TwHt3FLzt" - Local tower yaw (or torsional) force of tower gage 3
  "TwHt3MLxt" - Local tower roll (or side-to-side) moment of tower gage 3
  "TwHt3MLyt" - Local tower pitching (or fore-aft) moment of tower gage 3
  "TwHt3MLzt" - Local tower yaw (or torsional) moment of tower gage 3
  END of OutList section (the word "END" must appear in the first 3 columns of the last OutList line)
  ====== Outputs for all blade stations (same ending as above for Spn1.... =========================== [optional section]
  1 BldNd_BladesOut - Number of blades to output all node information at. Up to number of blades on turbine. (-)
  "All" BldNd_BlOutNd - Future feature will allow selecting a portion of the nodes to output. Not implemented yet. (-)
  OutList - The next line(s) contains a list of output parameters. See OutListParameters.xlsx for a listing of available output channels, (-)
  END (the word "END" must appear in the first 3 columns of this last OutList line in the optional nodal output section)

---

• Case 2
  ---------------------- INITIAL CONDITIONS --------------------------------------
  0 OoPDefl - Initial out-of-plane blade-tip displacement (meters)
  0 IPDefl - Initial in-plane blade-tip deflection (meters)
  0 BlPitch(1) - Blade 1 initial pitch (degrees)
  0 BlPitch(2) - Blade 2 initial pitch (degrees)
  0 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)
  12.1 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)
  -0.00702 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)

All settings other than those described above were configured with the same values as in Case 1.

[JongHoon-Jeong]

To add one more note regarding 2., NDiv was set to 1 in SubDyn.

[jjonkman]

Dear @JongHoon-Jeong,

Regarding (1), do the solutions eventually converge to similar answers for NDiv = 2 and 4 with Nmodes = 8 (i.e. can you share your table of results 100 or so seconds into the simulation)? I'm not aware of any issues with the 6 Guyan or first 8 Craig-Bampton modes; our concerns are with the higher modes that were triggering warnings about their eigenvalues, but not including these modes is a good solution (I'm not sure why you increased Nmodes in the first place). Also, could you try looking at the nodal loads in a member lower in the jacket; I'm curious if there is something unique in the outputs for members attached to the interface joints?

Regarding (2), does plotting the solution with WindType = 1 and WaveMod = 0 compared to the solution with wind and wave excitation offer any clue as to the length of the start-up transient?

Best regards,

[JongHoon-Jeong]

Dear Dr. Jonkman,

I would like to wrap up our discussion on the issues I have been working on here.

Regarding issue number 1, after speaking with my academic advisor, I came to understand that the answer to my question lies in structural analysis theory: when an external force is applied at one end of a beam, an equal force acts at the opposite end to maintain equilibrium.

Regarding issue number 2, upon examining the graph results more carefully, I was able to see that a startup transient occurs at the very beginning. I believe it was not easy to notice because I was looking at approximately 3,600 seconds worth of data.

I am currently enrolled as a master's degree student in graduate school. As I still lack knowledge in many areas, I am afraid I may have caused you inconvenience by asking such burdensome questions during your busy schedule, and I sincerely apologize for that.

I am truly grateful for your consistent and kind responses throughout this discussion, and I sincerely hope that you remain in good health.

Thank you very much.