Provide openfast the motion of the floating platform through simulink (or some other way)

[cc200528]

Hello
I have started learning Openfast. I want to provide openfast the motion of the floating platform through simulink (or some other way) at every time step of the simulation, and openfast will give me the reaction force of the floating platform. At the same time, hydrodynamics and mooring will not affect the movement of the floating platform.

Key points of clarification:
To achieve my target I need to learn the development side of Openfast but I want to know where should I start.
Is it a difficult job and possible to be done in 2 months.
Can anyone gives me key step I have to follow to get to my target (just mention main things I have to learn to get to my target)
I will highly appreciate the expert's remarks and suggestions. Thanks

[jjonkman]

Dear @cc200528,

Regarding prescribing the platform motion in the ElastoDyn module of OpenFAST, this topic has been discussed previously, e.g., see: #617.

Regarding learning OpenFAST, see a related question answered here: #1339. The new user documentation to be released in OpenFAST v4.0 is also a quite useful getting started guide: #308.

Best regards,

[cc200528]

Dear jjonkman,
Thank you for your answer. It was very helpful.
But I still have some questions, what I want to know is, If I want to use ExtPtfm module to prescribe an existing semi-submersible floating platform motion in r-test, what should I do? Do I need to produce the reduced matrices (M,C and K) and reduced loads for the floating platform using a high-fidelity FEM software.
Please give me help and provide me with the specific key steps of useing ExtPtfm module to prescribe an existing semi-submersible floating platform motion.

[jjonkman]

Dear @cc200528,

The ExtPtfm module of OpenFAST is useful if you are using a sequentially coupled workflow, in which you generate or are given the reduced matrices (M, C, K) and reduced loads (F), of the substructure. NREL has not provided software for you to generate these matrices/vectors, but if you are using a sequentially coupled workflow, I would assume you are using other software that would generate these for you. If you are not using other software, I would suggest modeling the substructure directly in SubDyn/HydroDyn/MoorDyn rather than using ExtPtfm.

FYI: A sequentially coupled workflow is more commonly used in fixed-bottom wind than it is in floating wind, given the more active coupling between the turbine and floater in floating wind.

Best regards,

[cc200528]

Dear jjonkman,
I'm coming back to you to report my progress on this. I used to try adding ExtPtfm to a semisubmersible floating offshore wind system.The following is the Guyan input file.

I shut down five platform freedoms except PtfmPitch. I have a question, when I change the value of the K matrix or the C matrix, the result of PtfmPitch does not change, why?When I change the M matrix or F, the value of PtfmPitch changes.
Best regards,

[jjonkman]

Dear @cc200528,

I'm not sure. I would expect the ExtPtfm mass, damping, stiffness, and force to all play a role in the platform-pitch response.

Best regards,