Question about the wind load calculation

[Jiang990109]

Hi, I am currently conducting a quasi-static mooring analysis for the IEA 15MW reference wind turbine on a semi-submersible platform.

For the turbine's operational state, the aerodynamic thrust force in the surge direction can be readily calculated using the thrust coefficient (CT), which is a known function of wind velocity, as outlined in standards such as DNV-RP-C205.

However, my analysis also requires assessing the system's response under extreme environmental conditions, specifically a 50-year return period wind event. In such conditions, the wind turbine would be in a parked (or idling) configuration with its blades feathered. In this state, the operational CT curve is no longer applicable.

Could you please provide guidance, established methodologies, or relevant data sources for calculating the total aerodynamic wind load in the surge direction on the parked wind turbine system (including the rotor, nacelle, and tower)? I am specifically looking for appropriate drag coefficients(CD) projected area or reference thrust values for this parked condition.

[jjonkman]

Dear @Jiang990109,

Well, OpenFAST can be used to calculate the aerodynamic loads under both operational and parked/idling conditions.

You mention quasi-static analysis, but FYI, the dynamic response is likely important under extreme wind and wave conditions.

FYI: If the rotor is aligned with the wind and all blades are feathered, the thrust force on the rotor can be quite small even with extreme wind, with the thrust force on the nacelle and tower much more important. But if the rotor is not aligned with the wind or all blades are not feathered (e.g., due to pitch fault), the importance of rotor thrust grows. Again, all of these conditions can be considered in OpenFAST.

Best regards,