IEC Wind

To all, as a new user to FAST, CRUNCH and the like, i am having difficulty in deciding the best way to generate the IEC Wind output files i need. Im performing a rainflow counting analysis and therefore need a range of wind sppeds, 8-30m/s. could anyone please suggest the best way to do this? many thanks, teddy crockwell, merseyside, england

Hi Teddy,

I’m not exactly sure I understand your question, but hopefully this will help.

The IECWind program ( creates the deterministic wind fields for the Extreme operating gust (EOG), Extreme direction change (EDC), Extreme coherent gust with direction change (ECD), Extreme wind shear (EWS), and the steady Extreme wind speed model (EWM). These cases are for the ultimate loads, though, so you’re probably not doing rainflow counting with them. If you have questions about the program, David Laino is the guy to ask.

Rainflow cycle counting is used in fatigue analysis, which makes use of turbulent winds. For the turbulent cases (IEC’s Normal Turbulence Model [NTM], Extreme turbulence model [ETM] or the turbulent EWM), the wind files are generated in TurbSim ( To get these files, you will have to run several different random seeds for each wind speed required. Usually this will be done using a script that loops through each wind speed (in 2 m/s increments) and runs at least six 10-minute cases with different random seeds for that wind speed. The script should save the output summary and binary wind files someplace that can be accessed when FAST is run.

Marshall Buhl has written some Perl scripts that create the wind files and then run FAST and Crunch. They are a little outdated, but they can be a good starting place to figure out the process. The scripts (RunNTM or RunIEC) are also on our website: