Dear Jason Jonkman,

First of all congratulations for this forum, it is very useful. I work at IKERLAN, a research center, and I am studying the deflection failure on the wind turbine blades. We want to analyze the limit behavior of the 5 MW NREL Offshore blade. To develop this simulation we used the files from the âDefinition of a 5-MW Reference Wind Turbine for Offshore System Developmentâ article in FAST code. We would like to know your opinion about the options we choose to carry on these calculations and listen to any suggestions you could make.

After computing the different load cases based on the guidelines in IEC standards, we selected the worst extreme wind cases for flapwise and edgewise directions.

We selected two extreme winds, which are the boundary conditions of service:

âą Flapwise: EWM50 will be the worst case

âą Edgewise: ECD-R-2 will be the worst case

EWM50

For this case, we have assumed that the extreme situation would be when the blade is parked and the blade pitch angle is 0Âș, flat to the wind. We assume 0Âș pitch angle because it is worse than if the blade was feathered, 90Âș pitch angle. To achieve these conditions, we start with an initial zero rotor speed and mechanically actuated brake. The most significant changes in the FAST input file will be these ones:

PCMode 0

TimeGeOn 9999.9

THSSBrDp 0

TiDynBrk 0

TTpBrDp(1,2,3) 0

TBDepISp(1,2,3)0

BlPitch(1,2,3) 0

RotSpeed 0

HSSBrDT 0

Like you suggest in the NWTC forum, we also changed the Aerodyn input:

StallMod= Steady

IndMode=None

We would like to know if you think that these parameters have the correct value or term to achieve the condition of EWM50.

ECD-R-2

On the other hand, we choose the ECD-R-2 load case. At this extreme event due to a strong gust of wind of 26 m/s, the Vcut is exceeded. We have assumed that this event is short so the wind turbine operation will be normal, this way we want to obtain the most extreme case.

We are not sure if our hypothesis is correct, therefore, we would like to know your opinion about how to deal with this extreme event.

Thank you very much for your time,

Best regards,

Eneko Aritz