Simulating OC3 phase II coupled springs in FAST v7

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Satish.Jawalageri
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Re: Simulating OC3 phase II coupled springs in FAST v7

Postby Satish.Jawalageri » Thu Oct 08, 2020 7:09 am

Hi,

Could I know where I can edit the foundation properties and soil model in Openfast for 5MW_OC3Mnpl_DLL_WTurb_WavesIrr.fst?

Thanks,
Satish J

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Re: Simulating OC3 phase II coupled springs in FAST v7

Postby Jason.Jonkman » Thu Oct 08, 2020 8:05 am

Dear Satish,

This OpenFAST model of the NREL 5-MW turbine atop the OC3-monopile assumes a fixed (clamped) connection at the seabed. In the context of the IEA Wind Task 30 OC6 Phase II project, NREL has developed new functionality in OpenFAST for modeling soil-structure interaction, including the introduction of coupled springs in SubDyn, as well as a new module (SoilDyn) that supports both couple springs and an interface to the REDWIN soil-structure interaction superelement from NGI (and a placeholder for distributed springs in the future). This functionality has been made available to OpenFAST users in the OC6 Phase II project, but has not yet been merged into the Dev or Master branches of OpenFAST. Until then, OpenFAST only supports the apparent fixity model or the user-defined external platform.

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
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Re: Simulating OC3 phase II coupled springs in FAST v7

Postby Satish.Jawalageri » Thu Oct 08, 2020 8:20 am

Dear Jason,

Thanks for your rely.

Okay, could I know where can I find apparent fixity model in the input files?

Could you please provide insights on user defined platform as how to consider in the main model?

Thanks,
Satish J

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Re: Simulating OC3 phase II coupled springs in FAST v7

Postby Jason.Jonkman » Thu Oct 08, 2020 8:33 am

Dear Satish,

You can define the apparent fixity in whichever structural module you are using to model the substructure (this would be SubDyn for the OC3 monopile, or ElastoDyn for a land-based system). Basically, define joints and members that extend below the seabed. This has been discussed multiple times on this forum.

The user-defined external platform is available by setting CompSub = 2 in the OpenFAST primary input file. More information on this model is provided in a recent discussion on OpenFAST github issues: https://github.com/OpenFAST/openfast/issues/549.

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: Simulating OC3 phase II coupled springs in FAST v7

Postby Satish.Jawalageri » Wed Oct 14, 2020 3:49 am

Dear Jason,

Thanks for your reply.

Right now, I am concentrating on monopile structure. If I want to do apparent fixity, just changing the joints and members in subdyn is sufficient?
Where can I change the stiffness and mass properties?

Could you please elaborate on this or could you please provide any reference?

Thanks,
Satish J

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Re: Simulating OC3 phase II coupled springs in FAST v7

Postby Jason.Jonkman » Wed Oct 14, 2020 8:55 am

Dear Satish,

Yes, the joint locations and member (beam) properties of the monopile substructure are set within the SubDyn input file. The SubDyn documentation has not yet been ported to OpenFAST's online readthedocs documentation, but you find the SubDyn documentation associated with FAST v8 (which should apply to OpenFAST v2.4) 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

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

Re: Simulating OC3 phase II coupled springs in FAST v7

Postby Satish.Jawalageri » Wed Oct 14, 2020 9:01 am

Dear Jason,

Thanks for your reply.
Does that mean just changing the joints and member properties (increasing the length below the seabed) will be sufficient for apparent fixity model?

And I see somewhere that we should update the mode shape coefficients in elastodyn, Do we need to do this or I might misinterpreted.

Thanks,
Satish J

Jason.Jonkman
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Re: Simulating OC3 phase II coupled springs in FAST v7

Postby Jason.Jonkman » Wed Oct 14, 2020 10:39 am

Dear Satish,

Yes, your understanding of the apparent fixity model is correct.

If the stiffness of the substructure changes in SubDyn, and if you are modeling the tower in ElastoDyn, then yes, ideally you'd change the mode shapes of the tower in ElastoDyn accordingly. This has been discussed several times on this forum. (Of course, if the stiffness change is small, as it may be for an apparent fixity approach, the impact on the mode shapes may be negligible.)

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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