model Validation

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Satish.Jawalageri
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Re: model Validation

Postby Satish.Jawalageri » Fri Oct 16, 2020 9:43 am

Dear Jason,

Thanks for your reply.

Yes. But fore-aft bending moment is decreasing with as I have consider the wave properties to be constant throughout the simulation time (hence it should not decrease right?) and what might be the solution for this and wave elevation?

Thanks,
Satish J

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Re: model Validation

Postby Jason.Jonkman » Fri Oct 16, 2020 9:50 am

Dear Satish,

I suppose you are referring to the start-up transient in the mudline moment (and other outputs) that occurs over the first 30 s or so of the simulation? These happen in all simulations and can be reduced by choosing initial conditions that are more line with their expected values for a given simulation. Regardless, the start-up transients were eliminated in the OC3 Phase I results, i.e., by not outputting data until after the start-up transient has ended (e.g., by setting TStart > 30 s).

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

Satish.Jawalageri
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Re: model Validation

Postby Satish.Jawalageri » Mon Oct 19, 2020 2:37 am

Dear Jason,

Thanks for your reply.

I have attached servodyn file where I have considered TStart as 30sec (but it says unused).

- What might be the case in the wave elevation?

- Do I get the input files used for phase 1 load case 5.1?

Thanks,
Satish J
Attachments
NRELOffshrBsline5MW_OC3Monopile_ServoDyn.rtf
(11.43 KiB) Downloaded 10 times

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Re: model Validation

Postby Jason.Jonkman » Mon Oct 19, 2020 7:10 am

Dear Satish,

TStart is an input parameter in the OpenFAST primary (*.fst) file, not in ServoDyn.

I don't really understand your other questions.

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

Satish.Jawalageri
Posts: 78
Joined: Sun May 31, 2020 4:57 am
Organization: University College Dublin
Location: Ireland

Re: model Validation

Postby Satish.Jawalageri » Mon Oct 19, 2020 7:19 am

Dear Jason,

Thanks for your reply.

Satish.Jawalageri wrote:Dear Jason,

Continued....I couldn't able to add more than 3 files in my previous post. So I am attaching the result and fast file.

Thanks,
Satish J


Following the above quoted post, how can I get the wave elevation sinusoidal?

Thanks,
Satish J

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Re: model Validation

Postby Jason.Jonkman » Mon Oct 19, 2020 8:06 am

Dear Satish,

Your waves are not sinusoidal because you've enabled second-order wave kinematics. Disabling second-order wave kinematics (WvDiffQTF = WvSumQTF = False) will result in a sinusoidal wave elevation.

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

Satish.Jawalageri
Posts: 78
Joined: Sun May 31, 2020 4:57 am
Organization: University College Dublin
Location: Ireland

Re: model Validation

Postby Satish.Jawalageri » Mon Oct 19, 2020 10:41 am

Dear Jason,

Thanks for your reply.

Okay, got that.

Jason.Jonkman wrote:Dear Satish,

OK, thanks for clarifying.

One big difference I see is that the original OC3 Phase I results for load case 5.1 assumed wave linearity (Airy waves). However, I see that you have enabled second-order wave-kinematics (WvDiffQTF = WvSumQTF = TRUE) in your analysis (hence why your wave elevation is not sinusoidal). The second differences is in regards to wave stretching. The original OC3 Phase I results included Wheeler stretching for the wave kinematics, however, this functionality is not available in the version of OpenFAST that you are running. The lack of Wheeler stretching will impact the wave loads and resulting bending moment at the mudline.

Best regards,


- Does this result attached is correct? (I have attached plots resulted my simulation and the referred simulation results)

- Do I get any reference where I can validate this OpenFast model?

Thanks,
Satish J
Attachments
Screenshot (62).png
Result from referred simulation
Screenshot (62).png (31.07 KiB) Viewed 352 times
Screenshot (63).png
Screenshot (63).png (22.53 KiB) Viewed 352 times

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Re: model Validation

Postby Jason.Jonkman » Mon Oct 19, 2020 11:06 am

Dear Satish,

Your results make sense. You are getting a lower amplitude of mudline fore-aft bending moment because version of HyrdoDyn you are using in OpenFAST does not inherently consider wave stretching, which are included in the results you are comparing to.

If you need to match the OC3 results exactly, until wave stretching is added to OpenFAST*, you could apply wave stretching yourself and use the corresponding wave kinematics within OpenFAST using the WaveMod = 6 option of HydroDyn. This would require that you have wave kinematics at all hydrodynamic analysis nodes along the monopile.

Best regards,

Footnote:
*NREL did have a project to add wave stretching into OpenFAST, but the project ran out of funding before a successful completion, and the solution was not numerically stable for structural flexible substructures; and we have not yet been funded to restart and finish the project.
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

Satish.Jawalageri
Posts: 78
Joined: Sun May 31, 2020 4:57 am
Organization: University College Dublin
Location: Ireland

Re: model Validation

Postby Satish.Jawalageri » Tue Oct 20, 2020 2:18 am

Dear Jason,

Thanks for your reply.

Okay, Then Is the solution I obtained is acceptable without wheeler stretching as it is getting difference of around 20000 KNm? Any recommendation on going ahead with this solution or the software version itself (Openfast)?

I can use all these in Fastv8 right? If so, could you provide me the link where I can download the Fastv8?

Thanks,
Satish J

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Re: model Validation

Postby Jason.Jonkman » Tue Oct 20, 2020 6:26 am

Dear Satish,

Not including Wheeler stretching will result in a lower amplitude of wave loading. But Wheeler stretching is known to overpredict the wave loading amplitude anyway. I already suggested the use of WaveMod = 6 in OpenFAST as a way to apply stretching, if needed.

I don't see any reason for you to run FAST v8 since you are already running a newer version--OpenFAST. And downgrading to FAST v8 would require some small input file changes. FAST v8 does not support Wheeler stretching either (but FAST v7 did). Regardless, FAST v8 is available here: https://drive.google.com/drive/folders/ ... sp=sharing.

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

Satish.Jawalageri
Posts: 78
Joined: Sun May 31, 2020 4:57 am
Organization: University College Dublin
Location: Ireland

Re: model Validation

Postby Satish.Jawalageri » Wed Oct 21, 2020 2:34 am

Dear Jason,

Thanks for your suggestions.

Okay, Could you please give suggestions on how to generate wave kinematics at all hydrodynamic analysis nodes along the monopile?

Thanks,
Satish J

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Re: model Validation

Postby Jason.Jonkman » Wed Oct 21, 2020 6:47 am

Dear Satish,

The hydrodynamic analysis node locations are written to the HydroDyn summary file. You'd presumably need access to a software that can calculate wave kinematics (including stretching) at these locations. NREL has not provided such a software.

The HydroDyn module of OpenFAST can output wave kinematics at the various hydrodynamic analysis nodes. So, with a bit a scripting, you could probably output these, apply a stretching theory, and write the stretched wave data to the wave kinematics input file formats the WaveMod = 6 option requires.

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

Satish.Jawalageri
Posts: 78
Joined: Sun May 31, 2020 4:57 am
Organization: University College Dublin
Location: Ireland

Re: model Validation

Postby Satish.Jawalageri » Wed Oct 21, 2020 10:29 am

Dear Jason,

Thanks for your suggestions.

Thanks,
Satish J

Satish.Jawalageri
Posts: 78
Joined: Sun May 31, 2020 4:57 am
Organization: University College Dublin
Location: Ireland

Re: model Validation

Postby Satish.Jawalageri » Tue Nov 03, 2020 6:24 am

Dear Jason,

Could I know where can I get the wave kinematics input file format when WaveMod=6.

Dear Satish,

The hydrodynamic analysis node locations are written to the HydroDyn summary file. You'd presumably need access to a software that can calculate wave kinematics (including stretching) at these locations. NREL has not provided such a software.

The HydroDyn module of OpenFAST can output wave kinematics at the various hydrodynamic analysis nodes. So, with a bit a scripting, you could probably output these, apply a stretching theory, and write the stretched wave data to the wave kinematics input file formats the WaveMod = 6 option requires.

Best regards,

Thanks,
Satish J

Jason.Jonkman
Posts: 5300
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: model Validation

Postby Jason.Jonkman » Tue Nov 03, 2020 6:36 am

Dear Satish,

You'll need 8 files to specify user-generated wave kinematics via WaveMod = 6: 3 for the wave particle velocities (*.Vxi, *.Vyi, *.Vyi), 3 for the wave particle accelerations (*.Axi, *.Ayi, *.Azi), 1 for dynamic pressure (*.DynP), and 1 for the wave elevation (*.Elev). Examples of these files are provided in Test_004 in the standalone HydroDyn CertTest from FAST v8. The draft HydroDyn User's Guide and Theory Manual provides some more information on these input files. The HydroDyn archive and documentation from FAST v8 are available on my Google drive: https://drive.google.com/drive/folders/ ... sp=sharing.

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


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