Simulation length for FOWT


I have a question on the needed simulation length for a floating offshore wind turbine with turbulent wind and irregular waves.

In DNV-OS-J103 Design of Floating Wind Turbine Structures 6.2.1 (p.41) it is stated, that simulations should be made for at least 3 hours and not only 10 minutes as it is common for onshore turbines.
But then in NREL/CP-5000-58153 (Simulation-Length Requirements in the Loads Analysis of Offshore Floating Wind Turbines) it is concluded, that 10 min duration is sufficient for transient simulations and that the method of treating unclosed cycles is more important (for fatigue).

In the later document some method of producing “Periodic Wind Files” is used.
Can anyone comment what simulation length and how many seeds should be used in order to capture also low frequent effects?
I am a little bit confused by that.

Thank you and best wishes,

Simon Wiedemann

Dear Simon,

At this time, I don’t think anyone can offer specific recommendations on the exact simulation length that is sufficient for loads analysis of floating offshore wind turbines (FOWTs). We have taken the results of our research project documented in NREL/CP-5000-58153 (and related publications) to write the section on simulation requirements for the draft IEC Technical Specification (61400-3-2) for the design of FOWTs (this TS is currently under review, hopefully to be published later this year). Here is what is relevant text written regarding this topic (from section 7.5.6):

And from section 7.6.3:

I hope that helps.

Best regards,

Thank you for clarification!
Is there in Turbsim an option to calculate periodic wind files?

Best regards,


Dear Simon,

The ability to generate periodic wind files was introduced in TurbSim v2.00 and newer, available from here: Simply set TurbSim input UsableTime to the string, “ALL” and run TurbSim to generate periodic wind data files useable by FAST.

Best regards,

Hi Jason,

I have been reading a paper that you are a co-author of, ref OMAE 2013-11397 ‘Simulation length requirements in the loads analysis of offshore floating wind turbines’.

Within that it states that 10 minute periodic wind files were used to generate the simulations, some 6hr, 3hr, 1hr, 20min and 10mins.
It also states that there are 10 wind seeds for each 100 min wind bin.

Also in the information you provide in this thread it says:



However I am a little confused on how using a periodic wind file for say a 1 hour simulation can achieve this? Is it not the same as running 6 x the same 10 min simulation, such that you only have one representative 10 min wind file? Am I missing something fundamental in the way the periodic wind file works or in the requirement for 10 minute wind seed representations for load analysis?

Thanks in advance for your help,

Dear Dawn,

Sorry, but I’m not sure I understand your question.

Running a 1-hour simulation with periodic 10-minute wind data means that there are 6 successive repetitions of the same 10-minute wind inflow, but other model parameters are likely different during the 1-hour simulation, including the incident wave elevation and structural response. For floating wind turbines, which tend to have platform natural frequencies that are very low in some modes of motion, there may only be a few oscillation cycles of these modes in a 10-minute simulation, but many more oscillations in longer simulations (hence the desire to check if the simulation length makes a difference versus simply running more 10-minute simulations).

Best regards,

Hi Jason,

Sorry, I worded that very badly. My question was what do we gain from a longer simulation when we are just repeating the same 10min wind profile, which you answered perfectly :slight_smile:

Many thanks,