Platform motion appears strange for an onshore wind turbine

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Jason.Jonkman
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Re: Platform motion appears strange for an onshore wind turbine

Postby Jason.Jonkman » Thu Jun 07, 2018 7:06 am

Dear Akshay,

By "the two models", I mean Test25 that NREL has distributed (model 1) and your model (model 2) are different.

I'm sorry, but I don't understand where you getting your numbers from. Where are you getting?
  • Total mooring pretension, T=6358481.025 N
  • Total Mass (Including water ballast), m=22043356 kg
  • Even if these values are correct, I'm not calculating T+mg = 137187702.505 N or V=13706.044 m3
(These don't seem to match the values given in the summary files.)

I'm also not sure where your file DeepCwind.MAP.sum came from. This appears to be a MAP++ summary file, but your FAST model says you are using MoorDyn instead of MAP++, so, I'm confused. I also noticed that your MoorDyn model uses an anchor depth of 200 m while your MAP++ model is using an anchor depth of 250 m.

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

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

Akshay.KumarKumawat
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Re: Platform motion appears strange for an onshore wind turbine

Postby Akshay.KumarKumawat » Tue Jun 12, 2018 3:07 am

Dear Dr Jason

I apologise you for inconvenience caused in the last post. here is new calculation in order to assure numerical stability for my model.
Tower-top Mass(kg) = 349389.844
Tower Mass(kg) = 249718.000
Platform Mass(kg) = 11322000.000
Total mass Incl. Platform(kg) = 11921108.000 or 116906133.768 (N).......(i)
As per NREL report, total vertical pretension weight = 1890000 (N).......(ii) (for DeepCwind)
As per HydroDyn section 6.8.3, (i)+(ii)=1025x9.80665xDisplaced volume(V=PtfmVol0)
118796133.768 = 1025x9.80665xV
V= 11818.375 m3
but now FAST is aborting and showing a FATAL error as following:

Timestep: 20 of 60 seconds. Estimated final completion at 13:58:60.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:InflowWind_CalcOutput:CalcOutput:IfW_Uni
formWind_CalcOutput:GetWindSpeed:Height must not be negative.
IfW_UniformWind_CalcOutput: Error calculating the wind speed at position (-9.6808, -15.227,
-0.11973) in the wind-file coordinates

FAST encountered an error at simulation time 20.825 of 60 seconds.
Simulation error level: FATAL ERROR

Aborting FAST.

Could you please suggest me what correction is required in the below attached input files in order to run complete simulation.
and could you please let me know where i can find explanation of MAP++ output file format.

Best regards
Akshay
Attachments
Test25_DeepCwind.zip
(758.23 KiB) Downloaded 101 times

Jason.Jonkman
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Re: Platform motion appears strange for an onshore wind turbine

Postby Jason.Jonkman » Tue Jun 12, 2018 10:59 am

Dear Akshay,

You are getting closer, but your platform is still not in vertical equilibrium. While I agree with your math, and I agree that the DeepCwind semi has a vertical mooring pretension of 1839000 N, I see that you have changed the vertical pretension in your model by changing the water depth (and anchor depth) from 200 to 250 m. Without redesigning the mooring system, the lines become more taught and the total vertical mooring pretension increases to 3*1006819.989 = 3020459.967 N (as reported in your MAP++ summary file). Thus, your system will still want to heave downward.

I also noticed that while you have now removed the water ballast from your HydroDyn model, you kept the effect of the ballast on the hydrostatic stiffness. Because you've removed the water ballast, you should also set the 6x6 matrix AddBLin to zero in your HydroDyn input file.

MAP++ is documented here: http://map-plus-plus.readthedocs.io/en/ ... index.html.

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

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

Mitesh.Ramani
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Re: Platform motion appears strange for an offshore 10MW DTU wind turbine(Spar Buoy)

Postby Mitesh.Ramani » Thu Nov 01, 2018 11:06 am

Dear Dr Jason

I am doing project on the offshore 10 Mw DTU wind turbine (Sparbouy).

I am getting problem while running the simulation and its I think problem of the system of vertical equilibrium.I have calculated the vertical mooring pretension.It is around =2294812.291 N for my system.Below I have attache the vertical force calculation and hydraulics calculation of my whole system.

Also without wind and waves I am not getting the platform motions close to 0.But my hydraulics calculation is look like a correct as you can see below i have attached the ballast below the Spar to system stay stable.

I am getting error as below,

Timestep: 28 of 50 seconds. Estimated final completion at 23:53:52.

FAST_Solution:CalcOutputs_And_SolveForInputs:SolveOption2:InflowWind_CalcOutput:
CalcOutput:IfW_Uni
formWind_CalcOutput:GetWindSpeed:Height must not be negative.
IfW_UniformWind_CalcOutput: Error calculating the wind speed at position (14.773
, -21.826,
-0.14772) in the wind-file coordinates

FAST encountered an error at simulation time 28.663 of 50 seconds.
Simulation error level: FATAL ERROR

Aborting OpenFAST



Also i have attached my inputs files as below.

I hope you can guide me to solve my this problem as soon as possible.

Thank you so much

Best Regards
Mitesh Ramani
Attachments
InputFiles.zip
Inputfiles
(18.2 KiB) Downloaded 85 times
Vertical force at fairlead.xlsx
Vertical force at fairlead
(10.26 KiB) Downloaded 77 times
Hydrostatics Calculation .xlsx
Hydrostatcis Calculation
(12.28 KiB) Downloaded 76 times

Jason.Jonkman
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Re: Platform motion appears strange for an onshore wind turbine

Postby Jason.Jonkman » Thu Nov 01, 2018 12:44 pm

Dear Mitesh,

I don't see that you've attached the vertical equilibrium calculations or input files.

Regardless, I'm not sure how much your floating wind turbine is heaving in the OpenFAST model, but you should ensure that the lowest aerodynamic node (likely on the tower) in AeroDyn is well above the mean sea level (MSL) such that when the floating platform heaves downward, the lowest aerodynamic node does not pass below the water surface and fall outside the domain of the wind field.

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

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

Mitesh.Ramani
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Re: Platform motion appears strange for an onshore wind turbine

Postby Mitesh.Ramani » Thu Nov 01, 2018 3:06 pm

Dear Dr. Jason

Thank a lot for your kind reply. I really appreciate your answer.

Sorry for that,It could not open So I have attache the hydroDyn and MoorDyn file as below.

Also I have attached the platform surge, sway and heave motion picture without wave and wind (In the hydraustaics conditon)

Can you please check the system need any other calculation for the hydrostatic equilibrium.(I will upload the another files in the next question can you please have a look those too )

AS I am doing ptoject for 10MW DTU wind turbine so I am using the all the inout files from The DTU 10MW Reference Wind Turbine website.

I hope you will give me a positive answer.

thank a lot

Best Regards
Mitesh Ramani
Attachments
HydroDyn.docx
HydroDyn
(7.61 KiB) Downloaded 72 times
Platform motions .PNG
platform surge ,sway ,heave
Platform motions .PNG (46.97 KiB) Viewed 2736 times
MoorDyn.docx
MoorDyn
(3.02 KiB) Downloaded 72 times

Jason.Jonkman
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Re: Platform motion appears strange for an onshore wind turbine

Postby Jason.Jonkman » Thu Nov 01, 2018 3:33 pm

Dear Mitesh,

I see that you uploaded a figure of the platform sway, roll, and pitch motions, but I don't see the platform surge or heave motions. Platform heave seems to be most critical to respond to your question.

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

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

Mitesh.Ramani
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Re: Platform motion appears strange for an onshore wind turbine

Postby Mitesh.Ramani » Thu Nov 01, 2018 3:43 pm

Dear Dr. Jason

AS you told me to check the the lowest aerodynamic node likely on the tower in the AeroDyn file. I have checked that and Also I have uploaded which AeroDyn file I am using for a simulation.

OpenFAST having 10MW floating Wind Turbine.Tower hight is 115.63m with 10m base. Hub height is around 129m.

I hope you can guide me for this problem from my attached files.

Thank a lot

Best Regards
Mitesh Ramani
Attachments
ElastoDyn.rtf
Elastodyn
(27.05 KiB) Downloaded 72 times
AeroDyn.rtf
AeroDyn
(4.14 KiB) Downloaded 71 times
Hydrostatics Calculation .pdf
Hydrostatics calculation
(120.6 KiB) Downloaded 66 times

Mitesh.Ramani
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Re: Platform motion appears strange for an onshore wind turbine

Postby Mitesh.Ramani » Thu Nov 01, 2018 3:52 pm

Jason.Jonkman wrote:Dear Mitesh,

I see that you uploaded a figure of the platform sway, roll, and pitch motions, but I don't see the platform surge or heave motions. Platform heave seems to be most critical to respond to your question.

Best regards,

Dear Dr. jason

Really sorry for the inconvenient. I have uploaded the picture with the platfrom heave surge and sway motion.

Thank you so much

Best regards
Mitesh Ramani
Attachments
Platfrom Heave and surge and sway motion.PNG
Platfrom Heave and surge and sway motion.PNG (25.52 KiB) Viewed 2729 times

Jason.Jonkman
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Re: Platform motion appears strange for an onshore wind turbine

Postby Jason.Jonkman » Thu Nov 01, 2018 5:27 pm

Dear Mitesh,

Looking at your platform-heave plot, the model clearly does not have the proper hydrostatic restoring in heave, and the system is falling due to gravity without proper buoyancy.

I only took a brief look at your files, but I see the main problem. You've set up your HydroDyn input file to be a strip-theory only model. However, you have not defined any hydrostatic restoring for this strip-theory model. See section 6.8.3 of the draft HydroDyn User's Guide and Theory Manual for more information: https://wind.nrel.gov/nwtc/docs/HydroDyn_Manual.pdf.

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

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

Mitesh.Ramani
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Re: Platform motion appears strange for an onshore wind turbine

Postby Mitesh.Ramani » Sat Nov 03, 2018 12:25 pm

Thank you for your reply,

I have Defined the hydrostatic restoring matrix non-zero term and I would like to show the calculation its given as below,

Density ρ=1025 kg/m3
Gravity g=9.81 m/s2
Water plane area A=54.10 m2 (=pi*D2/4,D=8.3)
Displaced volume V= 13085.4 m3
Metacentric Height GM=12.4m
C33=544050.2 N (ρgA)
C35=C53=0
C55=C44=1649987792 N(ρgV*GM)

After the add my new value I am getting the error in the OpenFAST as below,


"FAST_Solution:FAST_AdvanceStates:ED_ABM4:ED_AB4:ED_CalcContStateDeriv:SetCoordSy
:Small angle
assumption violated in SUBROUTINE SmllRotTrans() due to a large blade deflection
(ElastoDyn
SetCoordSy). The solution may be inaccurate. Simulation continuing, but future w
arnings from
SmllRotTrans() will be suppressed.
Additional debugging message from SUBROUTINE SmllRotTrans(): 2.75000E-02 s

MD_UpdateStates: NaN state detected.

FAST_Solution:FAST_AdvanceStates: MD_UpdateStates: NaN state detected.


FAST encountered an error at simulation time 3.75000E-02 of 50 seconds.
Simulation error level: FATAL ERROR"

Also I would like to ask that can you share any HydroDyn file for 10MW with Spar-buoy if it is possible so I can compare some data too for stability,Or can you please help me out now where I am going wrong.

I have attached my HydroDyn file as below kindly find it.

I hope you will help me out from this problem as soon as possible.

Thank again to guide me.
Attachments
HydroDyn_New Metrix.rtf
(18.26 KiB) Downloaded 67 times

Jason.Jonkman
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Re: Platform motion appears strange for an onshore wind turbine

Postby Jason.Jonkman » Sun Nov 04, 2018 5:52 pm

Dear Mitesh,

I see two problems:
*You have not changed the correct matrix. From your HydroDyn input file, I see that you changed the additional linear damping matrix, not the additional linear stiffness matrix. (And you have not changed the correct terms; you should only need to change AddCLin(3,3), AddCLin(4,4), and AddCLin(5,5).
*The body weight (gravity) term is intrinsically included in the ElastoDyn module. Only the buoyancy term should be included in the AddCLin matrix (and so the AddCLin(4,4) and AddCLin(5,5) terms should be negative valued for a deep-drafted spar). This topic is described in Section 6.8.3 of the draft HydroDyn User's Guide and Theory Manual that I referenced earlier.

I have not modeled the DTU 10-MW turbine atop a floating platform, but I'm sure these are available in the research community.

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

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

Mitesh.Ramani
Posts: 29
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Re: Platform motion appears strange for an onshore wind turbine

Postby Mitesh.Ramani » Mon Nov 05, 2018 9:48 am

Dear Dr. jason

Thank you very much for your continues support and help.

I am really sorry for that, I have corrected those data in that matrix and I have added the those value in the additional linear stiffness matrix.
Also I have corrected my calculation and it is give as below.

c33=54450 N\m
c44= -8846126298 N\m
c55= -8846126298 N\m

I was trying to do simulation with ElastoDyn,SeroDyn,HydroDyn and MoorDyn without wind and waves but I am getting the error like as below attached picture. Can you please help me out where I am going wrong.

I have attached the picture of the error, Input files and HydroDyn file as below kindly find it.

I hope you can guide me for my this problem as soon as possible.

I really appreciate your help.

Thank you

Best regards
Mitesh Ramani
Attachments
HydroDyn v2.docx
(30.67 KiB) Downloaded 62 times
Fast error.PNG
Fast error.PNG (39.61 KiB) Viewed 2699 times
Simulation17.7z
(269.82 KiB) Downloaded 59 times

Jason.Jonkman
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Re: Platform motion appears strange for an onshore wind turbine

Postby Jason.Jonkman » Mon Nov 05, 2018 10:17 pm

Dear Mitesh,

Your AddCLin matrix is still not specified correctly. You've defined the (2,3), (3,4), and (4,5) elements nonzero, when you should be specifying the (3,3), (4,4), and (5,5) elements nonzero.

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

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

Mitesh.Ramani
Posts: 29
Joined: Sat Oct 27, 2018 9:10 am
Organization: university of rostock
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Location: Rostock,Germany
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Re: Platform motion appears strange for an onshore wind turbine

Postby Mitesh.Ramani » Wed Nov 07, 2018 6:53 am

Dear Dr. jason

Thank you very much for correcting me and your help.

I really solved that problem and I have changed that matrix values as you told me.Till 50 time-step I am getting value around zero of platform motion.But if I increase the value of Total run time then at around 78 timestep I am getting the same error I have tried to fix that error but I could really find the solution.

have calculated Vertical force at the fairlead by hand and it is around =2294812.291 N
In the Fast MoorDyn summary it is around =2550000 N

I hope you can help me and guide me to solve this problem.

I have attached the error picture and HydroDyn and MoorDyn please kindly find it below.

Thanks again for your continuous help and support me.

Best Regards
Mitesh Ramani
Attachments
MoorDyn.rtf
MoorDyn
(2.84 KiB) Downloaded 39 times
HydroDyn.rtf
HydroDyn
(2.84 KiB) Downloaded 38 times
Error at timestep_78.PNG
Fast Error
Error at timestep_78.PNG (43.65 KiB) Viewed 2649 times


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