Error running HydroDyn file

Wind & Water Testing
1

Dear Dr. Jason,

I am doing project on STC platform.
I am getting problem while running the simulation and I couldn’t figure out the exact reason for the error. Please guide me to solve this.
The error is as follows:
Running FAST (v8.15.00a-bjj, 12-Apr-2016), compiled as a 32-bit application using single
precision
linked with NWTC Subroutine Library (v2.08.00, 5-Apr-2016)

Heading of the FAST input file:
FAST Certification Test #24: NREL 5.0 MW Baseline Wind Turbine with OC3 Hywind Configuration,
for use in offshore analysis

Running ElastoDyn (v1.03.02a-bjj, 8-Apr-2016).

Running AeroDyn (v15.02.03, 12-Apr-2016).

Running AirfoilInfo (v1.01.00a-bjj, 5-Apr-2016).

Running BEM (v1.01.00a, 12-Apr-2016).

Running InflowWind (v3.02.00a-bjj, 11-Apr-2016).
Opening InflowWind input file: .\5MW_Baseline/NRELOffshrBsline5MW_InflowWind.dat

Reading a 10x10 grid (160 m wide, 10 m to 170 m above ground) with a characteristic wind speed
of 8 m/s. This full-field file was generated by TurbSim (v1.50, 25-Sep-2009) on 06-Dec-2018 at
16:55:23.

Processed 289600 time steps of 80-Hz full-field data (3620 seconds).

Running ServoDyn (v1.05.00a-bjj, 11-Mar-2016).

Running ServoDyn Interface for Bladed Controllers (using Intel Visual Fortran for Windows,
14-Oct-2015).

Running HydroDyn (v2.05.00, 15-Mar-2016).
Generating incident wave kinematics and current time history.
forrtl: severe (59): list-directed I/O syntax error, unit -5, file Internal List-Directed Read
Image PC Routine Line Source
FAST_Win32.exe 012B66BB Unknown Unknown Unknown
FAST_Win32.exe 012B5140 Unknown Unknown Unknown
FAST_Win32.exe 024AF672 Unknown Unknown Unknown
FAST_Win32.exe 02496C92 Unknown Unknown Unknown
FAST_Win32.exe 0244B92B Unknown Unknown Unknown
FAST_Win32.exe 0174F785 MAIN_ 79 FAST_Prog.f90
FAST_Win32.exe 01530642 Unknown Unknown Unknown
FAST_Win32.exe 025F376F Unknown Unknown Unknown
KERNEL32.DLL 73D48484 Unknown Unknown Unknown
ntdll.dll 7743302C Unknown Unknown Unknown
ntdll.dll 77432FFA Unknown Unknown Unknown

Thank you

Best regards,
Sai Chaitanya

2

Dear Sai,

I’m not sure. Can you attach your HydroDyn input file?

Best regards,

3

Dear Dr. Jason,
I am herewith attaching the hydrodyn file.

Thank you

Best regards
Hydrodyn.docx (17.9 KB)

4

Dear Sai,

I don’t see any obvious problem from my quick review of your HydroDyn input file (but it is difficult to review in MS Word format). A similar question was asked and answered in the following forum topic: FAST error FORRTL. Perhaps the same solution applies to your case?

Best regards,

5

Dear Dr.Jason
I also had problems running the Standalone Hydrodyn , and I haven’t found the cause yet.I hope you can help me with this problem.
This Hydrodyn file is NRELOffshrBsline5MW_OC4Jacket_HydroDyn.dat
Error is as follows:

Running HydroDyn (v2.05.00, 15-Mar-2016).
Generating incident wave kinematics and current time history.

Error status and messages after execution:
ErrStat: 4
ErrMsg returned: HydroDyn_Init:Waves_Init:VariousWaves_Init:Cannot allocate array
InitOut%WaveVel.
VariousWaves_Init:Cannot allocate array InitOut%WaveAcc.
VariousWaves_Init:Cannot allocate array InitOut%PWaveVel0.
VariousWaves_Init:Cannot allocate array InitOut%PWaveAcc0.

Thank you
Best regards

6

Dear Chenxu Zhao,

Did you modify the HydroDyn file NRELOffshrBsline5MW_OC4Jacket_HydroDyn.dat in some way e.g. by increasing the number of hydrodynamic analysis nodes in the strip-theory solution or by modifying the wave definition in some way?

Best regards,

7

Dear Dr.Jason
Thank you very much for your reply
I used the HydroDyn file in test21 that comes with FAST V8 without modifying any data.
And I just added a driver file when running the Standalone hydrodyn(v2.05.00)

Best regards,

8

Dear Chenxu Zhao,

The error implies that you do not have enough memory to allocate more data. Did you recompile the standalone HydroDyn driver yourself? Have you tried to use the standalone HydroDyn driver for 64-bit Windows provided in the HydroDyn archive (HydroDynDriver_x64.exe)?

Best regards,

9

Dear Dr.Jason

Thank you very much for your reply. The problem was solved after I used HydroDynDriver_x64.exe.

Best regards,

10

Dear Dr. Jonkman,

I am doing project on Jacket platform(My jacket model is a little different from your model).I have successfully run FAST. However，I also had problems about FAST(v8.16.00a-bjj) ,I hope you can help me with these problems.
1)For no wave condtion.i can set CompHydro=0 in the FAST primary input file，But i find something wrong with my calculation of the tower top load .The primary file does not change, only changes HydroDyn.dat(WaveMod=0 or WaveMod=2 and Hs=0.0001m)The result seems to be right. how can i set ？
2)For no wind cindition.i can set CompInflow=0 and CompAero=0（It also needs to be set CompServo=0 ?) or The primary file does not change,i set WindType=1 and HWindSpeed=0.0001m/s(in InflowWind file)and WakeMod=0(in Aerodyn15 file).how can i set ?
3)I discussed the relationship between tower top load and wind speed in the case of no wave（i only set WaveMod=2 and Hs=0.0001m）. It seems that there are some problems when the wind speed is greater than 18m / s，and compared with your model under the same conditions.I have given the YawBrFxp, YawBrFyp, YawBrFzp results and the input files I was using. Am I using the proper input files?

Thanks in advance for any help and advice that can be offered.
jacket file.zip (215 KB)

11

Dear Ka.Chang,

Here are my answers to your questions:

  1. By “no waves”, do you mean still water or no water? To model still water, enable HydroDyn (CompHydro = 1) and set WaveMod = 0. To eliminate the water (and buoyancy), disable HyrdoDyn completely (CompHydro = 0).
  2. Similarly, by “no wind”, do you mean still air or no air? To model still air, disable InflowWind (CompInflow = 0), enable AeroDyn (CompAero = 2), and set WakeMod = 0 in AeroDyn. To eliminate air (modeling the wind turbine in a vacuum), disable both InflowWind and AeroDyn (CompInflow = CompAero = 0).
  3. I haven’t reviewed your model in detail, but I see two oddities in your results. First, there is a ringing in the vertical load, which implies that you haven’t initialized platform heave (PtfmHeave) in ElastoDyn to the expected equilibrium displacement (see the SubDyn documentation for details). Second, I see that the YawBrFxp shows a low RMS for the Test21 jacket model at high wind speeds; this suggest something wrong in the model set up (e.g., changing or disabling the controller), but it is hard for me to guess what the problem is.

Best regards,

12

Dear Dr. Jonkman,

Thank you very much for your reply.I am very sorry that I marked the RMS two curves incorrectly，The blue curve is Test21 Jacket model, and the red curve is my Jacket model.I revised it as you suggested and recalculated the PtfmHeave（ElastoDyn） and AddBLin（HydroDyn）value，The simulation results fluctuate in the equilibrium position. Do you think it is right？
The calculated YawBrFxp RMS curve is very similar to the original graph.I used the ServoDyn file in test21 that comes with FAST V8 without modifying any data.Some parameters of ElastoDyn are modified，What other parameters should I modify？
ElastoDyn File：
------- ELASTODYN v1.03.* 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)
---------------------- ENVIRONMENTAL CONDITION ---------------------------------
9.80665 Gravity - Gravitational acceleration (m/s^2)
---------------------- 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 --------------------------------------
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)
10.1 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)
-0.037674 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)
91.00 TowerHt - Height of tower above ground level [onshore] or MSL [offshore] (meters)
23.00 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)
23.00 PtfmCMzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform CM (meters)
23.00 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)
566000 PtfmMass - Platform mass (kg)
5.00288E+06 PtfmRIner - Platform inertia for roll tilt rotation about the platform CM (kg m^2)
5.00288E+06 PtfmPIner - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)
1.02298E+07 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)
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 ---------------------------------------------------
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)
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)
30 TStart - Time to begin tabular output (s) (currently unused)
5 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] (-)
0 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, (-)
“YawBrTDxp,YawBrTDyp,YawBrTDzp”
“YawBrTAxp,YawBrTAyp,YawBrTAzp”
“YawBrFxp , YawBrFyp , YawBrFzp” - Fore-aft shear, side-to-side shear, and vertical forces at the top of the tower (not rotating with nacelle yaw)
“YawBrMxp , YawBrMyp , YawBrMzp” - Side-to-side bending, fore-aft bending, and yaw moments at the top of the tower (not rotating with nacelle yaw)
“TwrBsFxt , TwrBsFyt , TwrBsFzt” - Side-to-side bending, fore-aft bending, and yaw forces at the mudline
“TwrBsMxt , TwrBsMyt , TwrBsMzt” - Side-to-side bending, fore-aft bending, and yaw moments at the mudline
“PtfmSurge, PtfmSway , PtfmHeave” - TP translational displacements
“PtfmRoll , PtfmPitch, PtfmYaw” - TP rotational displacements
END of input file (the word “END” must appear in the first 3 columns of this last OutList line)

Best regards,

tower top load curve.png
tower top load curve.png3216×2461 67.7 KB

13

Dear Ka.Ching,

I still see a bit of ringing in the vertical load, although much better than before. If you haven’t already, I would plot PtfmHeave and ensure that you have set its initial value in ElastoDyn to its expected mean value from the time series.

You still have not provided me with enough information to know why your model shows low RMS for YawBrFxp at high wind speeds. Again, I would guess that the controller is not responding properly. It sounds like you are using the same controller used in Test21; is this controller sufficient for your turbine? Have you set proper initial conditions for the rotor speed and blade-pitch angle in ElastoDyn (based on their expected mean values for each mean wind speed simulated)? Setting improper initial conditions for these values can lead to incorrect behavior in the controller response.

Best regards,

14

Dear Dr. Jonkman,

Thank you very much for your reply.I don’t know how to draw the curve about PtfmHeave. If you plot PtfmHeave, please give it to me for reference.

I will provide you some information to know why my model shows low RMS for YawBrFxp at high wind speeds.I don’t know if this information is useful enough for you.Firstly,The basic information of my model has been modified in subdyn and hydrodyn according to test21 Jacket format.The tower height was increased by 2m in turn（Aerodyn15）.Some parameters modified in ElastoDyn will be given below.secondly，I set up eleven wind speed bins of 2 m/s size, from the cut-in to cut-out wind speeds.
modified parameters in ElastoDyn：

   10.1   RotSpeed      - Initial or fixed rotor speed (rpm)

-0.00070 PtfmHeave - Initial or fixed vertical heave translational displacement of platform (meters)
91.00 TowerHt - Height of tower above ground level [onshore] or MSL [offshore] (meters)
23.00 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)
23.00 PtfmCMzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform
CM (meters)
23.00 PtfmRefzt - Vertical distance from the ground level [onshore] or MSL [offshore] to the platform
reference point (meters)
566000 PtfmMass - Platform mass (kg)
5.00288E+06 PtfmRIner - Platform inertia for roll tilt rotation about the platform CM (kg m^2)
5.00288E+06 PtfmPIner - Platform inertia for pitch tilt rotation about the platform CM (kg m^2)
1.02298E+07 PtfmYIner - Platform inertia for yaw rotation about the platform CM (kg m^2)

I later tried to set the RotSpeed from 10.1 rpm to 12.1 rpm without changing the blade pitch angle in ElastoDyn. The RMS result of YawBrFxp is similar to Test21 Jacket，however，I still have some questions .
(1) I want to ask you how to set the rotor speed and blade-pitch angle at low wind speed? I mean that is rotor speed and blade pitch angle at high wind speeds suitable for low wind speeds.
(2) How can i set proper initial conditions for the rotor speed and blade-pitch angle in ElastoDyn (based on their expected mean values for each mean wind speed simulated)? Is there a corresponding relationship between them? Please give me some detailed instructions.

Best regards,

15

Dear Ka.Chang,

To plot PtfmHeave, add this output to the ElastoDyn OutList, rerun the simulation and plot the result.

It sounds like you have not changed the rotor of the NREL 5-MW baseline turbine, so, the expected mean values of rotor speed and blade-pitch angle as a function of mean wind speed are given in Figure 9-1 of the NREL 5-MW specifications report: nrel.gov/docs/fy09osti/38060.pdf. Numerical values for above rated conditions–where you seem to be having trouble–are given in Table 7-1 of that report.

Best regards,

16

Dear Dr. Jonkman,

Thank you very much!

I revised it as you suggested and recalculated the PtfmHeave value.I think the simulation result should be correct.Do you think it is right？

As you mentioned，the expected mean values of rotor speed and blade-pitch angle as a function of mean wind speed are given in Figure 9-1 of the NREL 5-MW specifications report.I only modified the rotor speed and blade pitch angle，However，I noticed that there are other parameters(TTDspFA,TTDspSS，OoPDefl，IPDefl) that need to be modified in the ElastoDyn.

Best regards,

Tower Top Load curve.png
Tower Top Load curve.png3216×2461 67.5 KB

17

Dear Ka.Ching,

Indeed, YawBrFzp is looking much better now. A very small adjustment to the initial PtfmHeave could likely eliminate the small lingering ringing.

The initial rotor speed and blade-pitch angle (and platform heave when using SubDyn) are the most critical initial conditions to get correct for a fixed-bottom offshore wind simulation. You could set the intial blade and tower-top deflections to their expected mean values as well, which will further reduce the start-up transients, but not by much.

Best regards,

18

Dear Dr. Jonkman,

That’s very useful guidance on how to set the initial conditions in ElastoDyn.Thank you once again for your help.

Best regards,

19

Dear Dr. Jonkman,

I’m sorry to trouble you again.I found RAO of the tower top(YawBrTDxp) under the unit regular wave(Hs=2m).I can get the resonant frequency from RAO.I study the motion response of the tower top under wave（still air:set CompInflow=0,CompAero = 2 and WakeMod = 0）.condition i：regular wave（Hs=0.5m Tp=3.2258s/Resonance period），condition ii：Pierson-Moskowitz spectrum（Hs=0.5m Tp=3.2258s/Resonance period）.however，I found that regular wave wave can cause tower top resonance and irregular wave can’t cause resonance.Is the result reasonable？

I would be very happy if you could give me some guidance.
Best regards
tower top motion results.zip (199 KB)

20

Dear Ka.Chang,

A resonance response will be impacted by the amplitude of excitation at the resonance frequency and the damping of the system. I would assume the system damping is set the same between the regular and irregular wave simulations. However, the amplitude of excitation quite different in the two cases. In the regular wave case, all of the energy is concentrated at the resonant peak. In the irregular wave case, the energy is spread across a range of frequencies, with less energy at the resonant peak. I’m sure you can induce more resonance in irregular seas if you increase the wave energy / signficant wave height.

Best regards,