Imposed Motion in Surge to FOWT with Semisubersible Floater

Wind & Water
28

Dear Dr. @Jason.Jonkman,
Thanks for your previous response, I have following two more queries;

(1) I am running two different wind conditions; (1) 8 m/s (2) 14 m/s and some different wave conditions for study the impact of floater motion on the wake meandering. For 8 m/s, simulations are perfectly running with all the wave conditions.

However, when I study the 14 m/s (indeed the different file for 14 m/s has been generated using turbsim) with different wave conditions; I am getting an error.

1st wave conditions; Hs = 1.5 m and Tp = 8.0 sec (works fine with 14 m/s)
2nd wave conditions; Hs = 2.5 m and Tp = 9.5 sec (it does not work for 14 m/s), it is giving the following error;

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I have gone through similar topic already discussed on the forum; FAST.Farm - #178 by Younes.Oudich (note; in this discussion, the simulation was failing when waked flow of turbine 1 was reaching to turbine 2, but in my case, simulation has run already completed more than half of the total time for simulation)

Moreover, n this topic, two things are highlighted to tackle with such issue; (1) different ServoDyn files for different wind turbines (I already have this), (2) performing modeling of turbine blades using elastodyn instead of BeamDyn, I did not completely understand this; does this mean I need to replace the BeamDyn files in the .fst file (as highlighted in the below figure),

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(2)
The documentation for Fast.FARM has following recommendations;
for wake_mode =2, 3

  • dr < D/10 (12.6 for NREL 5MW)

  • DT_Low < dr/2*Vhub

in your this article; “Investigating the interactions between wakes and floating wind
turbines using FAST.Farm”, you have used dr = 13 (for curled wake model) and DT_low of 3.0 seconds (I hope I am not wrong). If following the recommendations of documentation to achieve the numerical stability of the simulations; DT_low for your studied wind conditions should be as; for 8 m/s → 0.8125 seconds, for 11.4 m/s → 0.5702 seconds and for 18 m/s → 0.3611 seconds or less than these values. How was numerical stability achieved using DT_low of 3 m/s? As in my simulations; I am studying 8 m/s and 14 m/s (if i keep same DT_low for 14 m/s as of 8 m/s (0.75), the simulation becomes unstable).

I truly appreciate your valuable time and consideration. Thanks.

Very Respectfully,
Muhammad Abdullah