How to input platform motions time series and observe the responses.

[Danupon.Subanapong]

Hello,
I am now working on Floating Offshore wind turbine modelling. I have to give FAST the platform motions as an input in order to see the responses caused by effect of floater motion. I have been using FAST for a while, but only see that FAST can give initial displacement(s). So, I would like to ask is there any way to input floater motions to FAST?
Thank you so much,
Best Regards,
Danupon Subanapong

[Jason.Jonkman]

Dear Danupon,

You cannot directly specify 6-DOF motion of the platform in FAST / OpenFAST without customization of the source code.

For the 3 platform translation modes, you can use FAST v7’s Seismic module to prescribe time histories of motion–please see my post dated Aug 29, 2012 in the forum topic found here for more information: Software Releases.

Related questions have been discussed on this forum e.g.:

Control for scaled-down 5MW NREL

Dear All, I am a Polish student (Lodz University of Technology) currently working on my Bachelor Thesis where I analyze a concept of multi-rotor wind turbines for deep off-shore application. The idea behind it is to replace the 5MW NREL wind turbine with a set of 7 smaller rotors (which in total give the same swept area as the baseline turbine), compare their energy production and design appropriate frame. I attempt to use FAST to evaluate performance of an individual rotor of MRWT. I already …

Imposing Estimated Motion to Bottom of the Tower

Dear Enes, What you are trying to do sounds similar to what is discussed in the following forum topic: Regarding Seismic Load by FAST code. I’d recommend against trying to prescribe the motion of the first tower node, which is related to both the platform and tower-mode degrees-of-freedom; instead, I suggest you prescribe the motion of the tower base, which is the platform in FAST. Best regards,

Rigid Wind Turbine with Harmonic Motions

Dear Sara, I agree with Gerrit that the displacement, velocity, and acceleration of a DOF should not be changed directly without considering whether the equations of motion are consistent with the specified motion. If you simply wish to prescribe a platform surge motion time-history, you can use FAST’s seismic loading module, which was developed for a related purpose. Please see my post dated Aug 29, 2012 in the forum topic found here for more information: Software Releases. Best regards,

Best regards,

[Danupon.Subanapong]

Dear Jason Jonkman,
Thank you so much for your quick reply. I understood that it is not possible in FAST/OpenFAST. However, I know that FAST has interface with Orcaflex. In Orcaflex, the motions can be specified as input. So, the tower load responses can be obtained from FAST output. However, as far as I’ve tried it has not been successful yet. Can you please give me some suggestion? I wonder if I can do this way or not.
Best Regards,
Danupon Subanapong

[Jason.Jonkman]

Dear Danupon,

I’m not familiar with that functionality of OrcaFlex, but I would be surprised if the motion of the platform in FAST / OpenFAST could be controlled by OrcaFlex. This is because the FAST / OpenFAST interface to OrcaFlex is set up to pass the platform motions from FAST / OpenFAST to OrcaFlex and the hydrodynamic and mooring applied loads are passed from OrcaFlex to FAST / OpenFAST.

Best regards,