Dear @Lixian.Zhang,
In addition to @Riad.Elhamoud’s suggestions, I would confirm that the TLCD motion is 90-degree phase shift from the surge motion for these cases.
Best regards,
Dear @Lixian.Zhang
I have reviewed your HydroDyn input file. Although i am using the version here, which is for OpenFAST v3.5, i was able to run the free decay test and everything went fine. I compared between your HydroDyn and mine and for me there are quite similar. Note that in the version here, there are two HydroDyn input files (one includes hybrid theory and the other one includes the strip theory) and both are fine where using both files, the platform pitch response dies out with time. Nothing odd to me.
I dont now why you obtain odd results when you are simulating platform pitch in a free decay test (without TLCD).
Please kindly find in the following the plot of the PSD of platform pitch response computed from the platform pitch free decay test where i used the HydroDyn input file based on the hydrid approach.
Best Regards,
Riad
Dear @Lixian.Zhang
I was reviewing what you have sent a couple of days ago and i domt see that you are doing a platform pitch free decay test (see Figures 1 and 3). Indeed a platform pitch free decay test starts with a non-zero value of platform pitch at time=0 and i see in the figures 1 and 3 that at time zero, the platform pitch starts from zero which is not a free decay test.
Best Regards,
Riad
Dear @Riad.Elhamoud , Dear @Jason.Jonkman ,
Following your suggestion, I calculated the PSD for the uncontrolled case. The peak frequency of the PSD is located at approximately 0.03662 Hz, as shown in the figure below:
Due to my oversight, the figures I posted a few days ago did not include the first few hundred seconds of the pitch free-decay time response. I would like to provide the following supplementary results for completeness:
Variation with the TLCD mass ratio（“TLCD-2” denotes a mass ratio of 2%）
Variation with the liquid-column height（“TLCD-20m” denotes a liquid-column height of 20 m）
In addition, I would like to ask whether there is any existing model or test case involving a TLCD applied to the 22-MW floating wind turbine, and whether any related results are available for reference.
Best regards,
Dear @Lixian.Zhang,
I’m not aware of an example of the IEA Wind 22-MW RWT with a TLCD.
Again, I suggest focusing on the simpler case of surge free-decay, and switch from a TLCD to a TMD; do you see the damping you expect in that case?
Best regards,
Dear @Lixian.Zhang
Maybe you can try to put the TLCD in the nacelle if you dont want to deal with TMD.
Best Regards,
Riad
Dear @Jason.Jonkman , Dear @Riad.Elhamoud ,
I really appreciate your attention to this issue and your helpful replies.Recently, I have been carrying out pitch free-decay vibration-reduction analyses of the floating wind turbine using a TMD. I found that when the TMD is placed at the center location of the original TLCD, a clear vibration-reduction effect can be observed, regardless of whether the TMD mass ratio, natural frequency, or damping ratio is varied. The results are shown below:
Variation with the TMD mass ratio (“TMD-0_5” denotes a mass ratio of 0.5%, and “TMD-1_0” denotes a mass ratio of 1%).
Variation with the frequency ratio (“TMD-0_9” denotes a ratio of the TMD natural frequency to the pitch natural frequency of 0.9) .
Variation with the damping ratio (“TMD-1_0” denotes a damping ratio of 1% ).
I have also included my TMD control input file below for your reference.
------- STRUCTURAL CONTROL (StC) INPUT FILE ----------------------------
Input file for tuned mass damper, module by Matt Lackner, Meghan Glade, and Semyung Park (UMass)
---------------------- SIMULATION CONTROL --------------------------------------
True Echo - Echo input data to <RootName>.ech (flag)
---------------------- StC DEGREES OF FREEDOM ----------------------------------
1 StC_DOF_MODE - DOF mode (switch) {0: No StC or TLCD DOF; 1: StC_X_DOF, StC_Y_DOF, and/or StC_Z_DOF (three independent StC DOFs); 2: StC_XY_DOF (Omni-Directional StC); 3: TLCD; 4: Prescribed force/moment time series; 5: Force determined by external DLL}
true StC_X_DOF - DOF on or off for StC X (flag) [Used only when StC_DOF_MODE=1]
fasle StC_Y_DOF - DOF on or off for StC Y (flag) [Used only when StC_DOF_MODE=1]
FALSE StC_Z_DOF - DOF on or off for StC Z (flag) [Used only when StC_DOF_MODE=1]
---------------------- StC LOCATION ------------------------------------------- [relative to the reference origin of component attached to]
0 StC_P_X - At rest X position of StC (m)
0 StC_P_Y - At rest Y position of StC (m)
-17 StC_P_Z - At rest Z position of StC (m)
---------------------- StC INITIAL CONDITIONS --------------------------------- [used only when StC_DOF_MODE=1 or 2]
0 StC_X_DSP - StC X initial displacement (m) [relative to at rest position]
0 StC_Y_DSP - StC Y initial displacement (m) [relative to at rest position]
0 StC_Z_DSP - StC Z initial displacement (m) [relative to at rest position; used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
"none" StC_Z_PreLd - StC Z pre-load (N) {"gravity" to offset for gravity load; "none" or 0 to turn off} [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
---------------------- StC CONFIGURATION -------------------------------------- [used only when StC_DOF_MODE=1 or 2]
6 StC_X_PSP - Positive stop position (maximum X mass displacement) (m)
-6 StC_X_NSP - Negative stop position (minimum X mass displacement) (m)
6 StC_Y_PSP - Positive stop position (maximum Y mass displacement) (m)
-6 StC_Y_NSP - Negative stop position (minimum Y mass displacement) (m)
5 StC_Z_PSP - Positive stop position (maximum Z mass displacement) (m) [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
-5 StC_Z_NSP - Negative stop position (minimum Z mass displacement) (m) [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
---------------------- StC MASS, STIFFNESS, & DAMPING ------------------------- [used only when StC_DOF_MODE=1 or 2]
426717.48 StC_X_M - StC X mass (kg) [must equal StC_Y_M for StC_DOF_MODE = 2]
0 StC_Y_M - StC Y mass (kg) [must equal StC_X_M for StC_DOF_MODE = 2]
0 StC_Z_M - StC Z mass (kg) [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
0 StC_XY_M - StC XY mass (kg) [used only when StC_DOF_MODE=2]
22591.07 StC_X_K - StC X stiffness (N/m)
0 StC_Y_K - StC Y stiffness (N/m)
0 StC_Z_K - StC Z stiffness (N/m) [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
29455.06 StC_X_C - StC X damping (N/(m/s))
0 StC_Y_C - StC Y damping (N/(m/s))
0 StC_Z_C - StC Z damping (N/(m/s)) [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
0 StC_X_KS - Stop spring X stiffness (N/m)
0 StC_Y_KS - Stop spring Y stiffness (N/m)
0 StC_Z_KS - Stop spring Z stiffness (N/m) [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
0 StC_X_CS - Stop spring X damping (N/(m/s))
0 StC_Y_CS - Stop spring Y damping (N/(m/s))
0 StC_Z_CS - Stop spring Z damping (N/(m/s)) [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
---------------------- StC USER-DEFINED SPRING FORCES ------------------------- [used only when StC_DOF_MODE=1 or 2]
False Use_F_TBL - Use spring force from user-defined table (flag)
17 NKInpSt - Number of spring force input stations
---------------------- StC SPRING FORCES TABLE -------------------------------- [used only when StC_DOF_MODE=1 or 2]
X F_X Y F_Y Z F_Z
(m) (N) (m) (N) (m) (N)
-6.0000000E+00 -4.8000000E+06 -6.0000000E+00 -4.8000000E+06 -6.0000000E+00 -4.8000000E+06
-5.0000000E+00 -2.4000000E+06 -5.0000000E+00 -2.4000000E+06 -5.0000000E+00 -2.4000000E+06
-4.5000000E+00 -1.2000000E+06 -4.5000000E+00 -1.2000000E+06 -4.5000000E+00 -1.2000000E+06
-4.0000000E+00 -6.0000000E+05 -4.0000000E+00 -6.0000000E+05 -4.0000000E+00 -6.0000000E+05
-3.5000000E+00 -3.0000000E+05 -3.5000000E+00 -3.0000000E+05 -3.5000000E+00 -3.0000000E+05
-3.0000000E+00 -1.5000000E+05 -3.0000000E+00 -1.5000000E+05 -3.0000000E+00 -1.5000000E+05
-2.5000000E+00 -1.0000000E+05 -2.5000000E+00 -1.0000000E+05 -2.5000000E+00 -1.0000000E+05
-2.0000000E+00 -6.5000000E+04 -2.0000000E+00 -6.5000000E+04 -2.0000000E+00 -6.5000000E+04
0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00 0.0000000E+00
2.0000000E+00 6.5000000E+04 2.0000000E+00 6.5000000E+04 2.0000000E+00 6.5000000E+04
2.5000000E+00 1.0000000E+05 2.5000000E+00 1.0000000E+05 2.5000000E+00 1.0000000E+05
3.0000000E+00 1.5000000E+05 3.0000000E+00 1.5000000E+05 3.0000000E+00 1.5000000E+05
3.5000000E+00 3.0000000E+05 3.5000000E+00 3.0000000E+05 3.5000000E+00 3.0000000E+05
4.0000000E+00 6.0000000E+05 4.0000000E+00 6.0000000E+05 4.0000000E+00 6.0000000E+05
4.5000000E+00 1.2000000E+06 4.5000000E+00 1.2000000E+06 4.5000000E+00 1.2000000E+06
5.0000000E+00 2.4000000E+06 5.0000000E+00 2.4000000E+06 5.0000000E+00 2.4000000E+06
6.0000000E+00 4.8000000E+06 6.0000000E+00 4.8000000E+06 6.0000000E+00 4.8000000E+06
---------------------- StructCtrl CONTROL -------------------------------------------- [used only when StC_DOF_MODE=1 or 2]
0 StC_CMODE - Control mode (switch) {0:none; 1: Semi-Active Control Mode; 4: Active Control Mode through Simulink (not available); 5: Active Control Mode through Bladed interface}
0 StC_CChan - Control channel group (1:10) for stiffness and damping (StC_[XYZ]_K, StC_[XYZ]_C, and StC_[XYZ]_Brake) [used only when StC_DOF_MODE=1 or 2, and StC_CMODE=4 or 5]
1 StC_SA_MODE - Semi-Active control mode {1: velocity-based ground hook control; 2: Inverse velocity-based ground hook control; 3: displacement-based ground hook control 4: Phase difference Algorithm with Friction Force 5: Phase difference Algorithm with Damping Force} (-)
0 StC_X_C_HIGH - StC X high damping for ground hook control
0 StC_X_C_LOW - StC X low damping for ground hook control
0 StC_Y_C_HIGH - StC Y high damping for ground hook control
0 StC_Y_C_LOW - StC Y low damping for ground hook control
0 StC_Z_C_HIGH - StC Z high damping for ground hook control [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
0 StC_Z_C_LOW - StC Z low damping for ground hook control [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
0 StC_X_C_BRAKE - StC X high damping for braking the StC (Don't use it now. should be zero)
0 StC_Y_C_BRAKE - StC Y high damping for braking the StC (Don't use it now. should be zero)
0 StC_Z_C_BRAKE - StC Z high damping for braking the StC (Don't use it now. should be zero) [used only when StC_DOF_MODE=1 and StC_Z_DOF=TRUE]
---------------------- TLCD --------------------------------------------------- [used only when StC_DOF_MODE=3]
7.9325 L_X - X TLCD total length (m)
6.5929 B_X - X TLCD horizontal length (m)
2.0217 area_X - X TLCD cross-sectional area of vertical column (m^2)
0.913 area_ratio_X - X TLCD cross-sectional area ratio (vertical column area divided by horizontal column area) (-)
2.5265 headLossCoeff_X - X TLCD head loss coeff (-)
1000 rho_X - X TLCD liquid density (kg/m^3)
3.5767 L_Y - Y TLCD total length (m)
2.1788 B_Y - Y TLCD horizontal length (m)
1.2252 area_Y - Y TLCD cross-sectional area of vertical column (m^2)
2.7232 area_ratio_Y - Y TLCD cross-sectional area ratio (vertical column area divided by horizontal column area) (-)
0.6433 headLossCoeff_Y - Y TLCD head loss coeff (-)
1000 rho_Y - Y TLCD liquid density (kg/m^3)
---------------------- PRESCRIBED TIME SERIES --------------------------------- [used only when StC_DOF_MODE=4]
1 PrescribedForcesCoord- Prescribed forces are in global or local coordinates (switch) {1: global; 2: local}
"TimeForceSeries.dat" PrescribedForcesFile - Time series force and moment (7 columns of time, FX, FY, FZ, MX, MY, MZ)
-------------------------------------------------------------------------------
Based on the above observations, would it be reasonable to think that there may be some issues with the TLCD performance in free-decay vibration reduction? If so, could this have a significant influence on the subsequent simulations under normal operating conditions? I would appreciate any suggestions you both may have on this.
In addition, I would like to ask whether there are any successfully validated TLCD results available for reference, either from free-decay simulations or from normal operating conditions.
Best regards，
Dear @Lixian.Zhang
Thank you for the simulations you have ran. Here is my comments and recommandations:
- I dont agree with your statment " a clear vibration-reduction effect can be observed, regardless of whether the TMD mass ratio, natural frequency, or damping ratio is varied". In general, the vibration mitigation increases with the mass ratio. But there is a limit beyond the TMD has a detrimental effect. I did not see it myself but it is my intuition.
Regarding the TMD frequency, it should be close or equal to the excited mode of your structure. And the results you provided confirm this. If you consider a frequency ratio of 50%, 20%, the TMD will not work and maybe the TMD will increase the vibration (expressed in terms of temporal standard deviation and not RMS). My advice is that “dont believe a lot of papers in literature” where sometimes you will find that the TMD works for all freqencies and for any load case. A TMD has a frequency band or bandwidth. Outside this frequency band, the TMD does not work and this frequency band is in the vicinity of the excited mode (in your case, it is platform pitch). Regarding the damping ratio, i agree that there is an optimal damping ratio that leads to the highest vibration mitigation. - Regarding your question about TLCD, i suggest to put it in the nacelle and tuning it to the excited mode which is platfrom pitch freqency and try to compute the PSD of the uncontrolled and controlled cases.
Besides, i will share soon the MATLAB scripts that i developed during my Ph.D. thesis where these scripts couple MATLAB and OpenFAST to calibrate the parameters of the omnidirectional TMD. If i have some time, i will test the TLCD as you pointed out.
Of course, under normal conditions, the sitaution is not ideal like a free decay test where aerodynamic damping develop and influence the efficiency of the energy dissipation device. I have written an article about the use of an omnidirectional TMD for bidirectional vibration and fatigue mitigation under misaligned wind and wave loadings that will appear soon.
To my knowledge, i dont know whether there are TLCD validated results.
Hope that helps.
Best Regards,
Riad
Dear @Lixian.Zhang,
I’m glad to see that you are getting TMD results that generally make sense to you. I’m now concerned that there is a problem with the TLCD implementation in OpenFAST. I’m not aware of issues with the TLCD implementation other than what is reported in #2896, but perhaps there are other issues that have not been reported? If you are familiar with the TLCD theory (from: 4.17.3. TLCD: Derivations of Equation of Motion — OpenFAST v5.0.0 documentation), perhaps you could review the StC source code for consistency.
The TLCD implementation in StC was based on the work of Semyung Park (PhD student) and Matt Lackner (Professor) at UMass. I would suggest reaching out to Matt Lackner to see if he has a good TLCD test case.
Best regards,
Dear @Lixian.Zhang
The article has just been published.
Here is the link to the article:
Happy reading 
Best Regards,
Riad