Where to define the cut-in and cut-out wind speed in TurbSim

Hello everyone,

I am now trying to use the FAST to calculate fatigue life of floating wind turbines. However, I met some problems in the simulation.

  1. I used TurbSim to generate a new wind speed input file, but I cannot find where to define the cut-in and cut-out wind speed. Because in the loads calculation, we need to take parked and Idling status into consideration. I wonder when the wind speed is out of the range(between cut-in and cut-out wind speed), does it still use the same method to calculate the loads in FAST?
  2. If I want to compare the different types of FWTs, which parameters should I change in the input file. In the former simulations, I just give the same wind and wave conditions.

Could someone help me solve the problems? Thanks a lot! :stuck_out_tongue:

Kind Regards
Junyi. Wu

Dear Junyi,

The cut-in and cut-out wind speeds effect the operational state of the wind turbine (start-up, optimize power, maintain rated power, idle, etc.), which effects how you set the control options and initial conditions in FAST for the load-case simulations. TurbSim only needs to know the wind speed and other atmospheric conditions, not the operational state of the wind turbine, and so, cut-in and cut-out wind speed are not specifically defined in TurbSim.

Changing the floating platform type would effect the structural, hydrodynamic, and mooring settings in the FAST input files.

Best regards,

Hi Jason,

Thanks for your quick reply. That is to say if I wonder simulate for 2 hours, I just use the wind data that generated from TurbSim and need not to consider whether the wind speed is in the range of
cut-in and cut-out wind speed ?

Thanks
Junyi

Dear Junyi,

I’m not sure I really understand your question. However, one would rarely run a 2-hour simulation in TurbSim. TurbSim is valid for stationary wind conditions, which typically last on the order of 10 minutes to 1 hour. Instead, to run simulations over a full range of wind speeds, one would normally run distinct TurbSim simulations at different mean wind speeds.

best regards,

Dear Jason,

Thanks for your help. I did run the case in different mean wind speeds and I will reduce the simulation time.

Best Regards
Junyi

Hello,
Sorry to disturb you guys. But, I am really confused with how to calculate the fatigue life of a wind turbine. Follow the IEC guidance, I know that I need to select DLCs from all design situations. So I just simply write down the steps that I think for calculating the fatigue life.

  1. Use TurbSim to generate wind file, from mean wind speed 4m/s to 24 m/s, and then determine the relative significant wave height and peak spectral period. ( Is it essential to use different Randseeds for each mean wind speed and is there any recommend simulation-length for each simulation?)
  2. Import the wind data in the FAST to get the loads and bending moments.
  3. Use MLife to calculate the fatigue life. ( Actually, I do not know which output from FAST can be used as input file for MLife for normal operation state or in idling state.
    Could you give me some advice please? Thanks a lot!

Kind Regards
Junyi. Wu

Dear Junyi,

You’re overall approach sounds correct, but the devil is in the details, and we don’t have the resources to offer detailed step-by-step guidance on performing a loads analysis. Of course, the loads-analysis requirements for offshore wind turbines are dictated by IEC 61400-3, which describes many details of the process. To answer your specific questions:

  • For the fatigue analysis of load case 1.2, each simulation is typically 10-min (600-s) long, after removal of start-up transients.
  • Each 10-min simulation should use different random seeds for the wind file and wave data.
  • MLife uses as input the time-series results from each load-case simulation from FAST typically for loads (forces/moments) at specific cross sections such as the blade root, shaft, tower-top, and tower-bottom, as well as blade-tip-to-tower clearance.

I hope that helps.

Best regards,

Dear Jason,

Thanks for your reply. I still have doubt about the last question. If I get the final output results from FAST, how can I know which result is used in operation state or which result is used in idling or parked state. For instance, in the Test 23 in MLife, the input files are DLC2.3_1.out and DCL2.3_1a.out for normal operation state and parked state seperately.I wonder what is the difference between these two files.

Regards
Junyi

Dear Junyi,

Perhaps Greg Hayman (who developed MLife) can comment further, but my guess is that the MLife CertTest is set-up more to test various features of the software than to be good examples for post-processing the results of a loads analysis. I looked briefly at Test23 and noticed that the files DLC2.3_1.out and DLC2.3_1a.out are actually identical.

In general, you should know when running FAST whether the simulation is for normal operation, parked/idling, or a discrete event, and so, you can locate the output files in the appropriate sections of the MLife input file.

Best regards,

Dear Jason,

Thanks for your help :smiley:

Kind Regards
Junyi