Coupling CFD code with FAST/OpenFAST

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Yingyi.Liu
Posts: 89
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Thu Nov 07, 2019 9:55 am

Dear Jason,

Is it possible to do a CFD+FAST/OpenFAST coupling in which the CFD code is only used to calculate the hydrodynamic loads of the platform?

The CFD code can be OpenFOAM, OceanWaves3D, etc. Have you ever heard of a similar research that was done by someone?

So, does SOWFA+OpenFOAM+FAST/OpenFAST serve for this purpose? I'm asking this question because SOWFA is usually used for evaluation of a wind farm performance. In another word, can SOWFA+OpenFOAM+FAST/OpenFAST be used for modeling the dynamics of a single floating wind turbine?

Thanks.
Yingyi
Last edited by Yingyi.Liu on Fri Nov 08, 2019 5:53 am, edited 3 times in total.

Jason.Jonkman
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Re: Coupling CFD code with FAST/OpenFAST

Postby Jason.Jonkman » Thu Nov 07, 2019 11:08 am

Dear Yingyi,

SOWFA is not developed to support the modeling of hydrodynamic loads via CFD. We have used OceanWaves3D to develop wave kinematics for use in FAST / OpenFAST, but in this case OceanWaves3D is used as a preprocessor, rather than directly coupled. I'm not aware of anyone who has coupled OpenFOAM to FAST / OpenFAST to support the modeling of hydrodynamic loads via CFD in a coupled simulation. That said, we have used OpenFOAM and STAR-CCM to model the hydrodynamic loads via CFD uncoupled from FAST / OpenFAST.

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

Yingyi.Liu
Posts: 89
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Re: Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Thu Nov 07, 2019 11:25 am

Dear Jason,

I'm sorry to have made you confused. Indeed, our purpose is to model a floating wind turbine in a nonlinear wave environment rather than linear. That means we need to substitute the linear wave kinematics with other nonlinear ones.

For such a purpose, what way of modeling do you recommend? I would like to hear your comments.

Thanks.

Yingyi

Jason.Jonkman
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Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Coupling CFD code with FAST/OpenFAST

Postby Jason.Jonkman » Thu Nov 07, 2019 11:37 am

Dear Yingyi,

What type of nonlinearities do you need? The HydroDyn module of FAST / OpenFAST support full second-order theory, including mean-dirft, slow-draft, and sum-frequency terms (both second-order wave kinematics for the strip-theory solution and second-order radiation/diffraction (QTFs) for the potential-flow solution). Do you need more nonlinearities than these models provide?

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

Yingyi.Liu
Posts: 89
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Re: Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Thu Nov 07, 2019 11:53 am

Dear Jason,

We hope to introduce fully nonlinear waves or strong nonlinear waves, at the later stage as well as some extreme waves, such as focused waves, solitary waves, etc. We hope to study the effect of wave nonlinearities on the dynamic response of a floating wind turbine.

Best regards,

Yingyi

Jason.Jonkman
Posts: 4338
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Coupling CFD code with FAST/OpenFAST

Postby Jason.Jonkman » Thu Nov 07, 2019 12:02 pm

Dear Yingyi,

What does your floating platform look like? Is it a thin body such as a spar buoy, which can be well simulated with the strip-theory solution? In that case, you can disable potential-flow and use OceanWave3D (or the like) as a preprocessor to generate nonlinear wave kinematics for use in FAST / OpenFAST.

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

Yingyi.Liu
Posts: 89
Joined: Thu May 01, 2014 3:16 am
Organization: Kyushu University
Location: Japan

Re: Coupling CFD code with FAST/OpenFAST

Postby Yingyi.Liu » Thu Nov 07, 2019 12:22 pm

Dear Jason,

Thanks. Indeed, we have not decided what a floating type to be used in this study. I can understand that the way you mentioned applies to a spar type.

But how about if the floater is a semisubmersible platform like the OC4 DeepCwind semi, combined by several columns and bracings, does the strip-theory solution still apply, or would it introduce large errors to your expectation?

For the details of the modeling, if we apply the strip-theory solution as you mentioned, should we input the nonlinear wave kinematics to FAST/OpenFAST via input files, or via a user-defined subroutine as the interface?

In addition, in the case if the interface is via input files, where can we find the format of these files? Thanks.

Best regards,

Yingyi
Last edited by Yingyi.Liu on Thu Nov 07, 2019 5:48 pm, edited 1 time in total.

Jason.Jonkman
Posts: 4338
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
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Re: Coupling CFD code with FAST/OpenFAST

Postby Jason.Jonkman » Thu Nov 07, 2019 1:18 pm

Dear Yingyi,

The strip-theory solution breaks down for large diameter / volume structures. I've been surprised how well the strip-theory-only solution has done modeling the OC4-DeepCwind semisubmersible, but getting the strip-theory model correct required knowledge of the added mass from the potential-flow solution. I would guess the strip-theory solution would break down for floating substructures larger than the OC4-DeepCwind semisubmersible.

User-defined wave kinematics can be specified through input files by enabling WaveMod=6. There are sample input files in the standalone HydroDyn CertTest in the standalone HydroDyn archive (https://nwtc.nrel.gov/HydroDyn). That said, the input file format would be a bit "clunky" for a semisubmersible model, which has many hydrodynamic analysis nodes.

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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