Dear Jason,

I am a FAST user and I met some problems when I used FAST to do some analysis on OC3-Hywind Spar, hoping to get some useful help and suggestions from you.

I used FAST to calculate the coupled dynamic responses of mooring line tension in time domain under the wind and wave load. JONSWAP spectrum and IEC Kaimai model which is calculated in Turbsim are adopted for simulating the random sea state. In the simulation the wind and waves are always from the same direction. I choose some sea state as example as following table list.

Sea state No. Wind speed Significant wave height Peak-spectral period Spectral bandwidth

22 6 1 6 0.999734

36 8 1 6 0.999722

48 10 1 6 0.999560

60 12 1 6 0.998924

69 12 7 14 0.998649

94 18 7 12 0.997909

because of the limited attachments of pictures,I add a word file to express my calculation and problems.

attachment of calculation .docx (479 KB)

After comparing the results, I have some problems.

- No matter how I change the wind and wave load in different sea state, the maximum PSD value occur in almost the same frequency which is at the range of 0.04-0.05rad/s. So I am no sure if the results I calculated are correct and reasonable?
- The maximum PSD value occur in low frequency which ranged in 0.04-0.05rad/s. The frequency is closed to neither wind frequency or wave frequency. So I feel puzzled by the results and I want you can give me some suggestions.
- The spectral bandwidth are all very closed to 1 which means it is the wideband, but for each sea state the value of spectral bandwidth is almost the same.so I am not sure about the results.
- Currently, I have used FAST to calculate totally 100 sea states which are based on the joint distribution model of wind and waves in the Northern North Sea to do a long-term analysis on mooring line tension. In each sea state, I just change the wind file in AD file and wave parameter in HD file, I am not sure if it is correct or not during my calculation. Should I change another parameter ?

Thank you for your kind advice.

Best regards,

Yanjian Wu