How to create an input file (.fst) for the case of Test 25?

Wind & Water Computer-Aided Engineering Software Tools
1

Hello Everyone,

Good noon! I hope you are kind of good. I have been doing my research on fatigue analysis of mooring line of FOWTs for test case no of 25. To achieve my results, my plan is as follows:

My plans:

  1. Wind Speed simulations (By TurbSim.inp (input file), where I can modify for several mean wind speed and run, afterwards I have got .bts file)

  2. That .bts file I have submitted in 5MW_Baseline folder. Then in the 5MW_Baseline folder I have modified inflowwind input file (.dat file) for several wind speed that I made by TurbSim.inp.

  3. Then I modified MoorDyn, and HydroDyn input file (.dat file) under 5MW_OC4Semi_WSt_WavesWN folder.

  4. Then I have modified 5MW_OC4Semi_WSt_WavesWN input file (.fst file)

  5. After simulation, I have found the Fairlead and anchor loads in MoorDyn output file (.sum file) that will be needed for calculating stress and number of cycles to failure for fatigue analysis.

My question:

  1. What I am trying to go forward is it right track to get fatigue?
  2. Here, I will go for 22 years simulations (5 years, 10 years, 16 years, 22 years) for fatigue purposes.
    Thank you and have a great day. When I go for modifying fst file, I have to change several parameters like Total run time (5 years), Recommended module time step (30 min). But it doesn’t work. Could you help me how can I solve this issue??
  3. Could you tell me where I can get .fst input file manual for test case of 25 as like TurbSim input guidelines manuals so that I can modify.
  4. Could you tell me where I can get .dat input file manual for HydroDyn, MoorDyn, and InflowWind as like TurbSim input guidelines manuals so that I can modify?
  5. Is it possible to do fatigue analysis of mooring line by MLife?

Regards
Raisul

2

Dear @JMRaisulIslam.Shohag,

Here are my responses to your questions:

  1. Yes, that sounds reasonable. Simulation requirements for calculating fatigue are dictated by IEC design standards, e.g. IEC 61400-3-2 for floating offshore wind turbines. These standards cover the conditions of interest that are likely fatigue driving, as well as the number and length of simulations required.
  2. You can’t run a single simulation for that long with such a large time step. The time step required in OpenFAST is commensurate with the characteristic frequencies of the response, including full-system natural frequencies and excitation frequencies (as discussed in other forum topics). Typically these are on the order of 10s of Hertz for a full-scale floating offshore wind turbine, requiring time steps on the order of 10s of milliseconds. Instead of running very long simulations, typically simulations are run on the order of 10 minutes to 1 hour and different simulations are run for different conditions (e.g., different mean wind speeds or different sea state severity).
  3. Documentation of OpenFAST is provided here: OpenFAST Documentation — OpenFAST v3.5.2 documentation
  4. Documentation of OpenFAST is provided here: OpenFAST Documentation — OpenFAST v3.5.2 documentation.
  5. MLife can do rainflowcycle counting and the computation of damage-equivalent loads and fatigue lifetime for any time series of loads.

Best regards,

3

Hi Dr. Jonkman,
Thank you for your response. Based on the answer of question 5, my question was: Can we do fatigue analysis mooring line of FOWTs for test cases of 25? I mean MLife can do fatigue analysis for any components of FOWTs??

4

Yes, that is correct.