Problems with making steady-state analysis

Wind & Water Computer-Aided Engineering Software Tools
1

Hi all,
I have some trouble with making steady-state analysis.
I don’t know how to make steady-state analysis and get the curves of rotor power vs wind speed, as shown below:
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To this problem, I have seen the discussion in the following forum post: viewtopic.php?f=4&t=666, in which Mr Jonkman said “we generated the results of Figure 9-1 by running a series of FAST with AeroDyn simulations at a number of given, steady, and uniform wind speeds. Separate simulations were run at each wind speed and each simulation was run long enough to ensure that all transient behavior had died out.” Is this mean we should make a time-marchiing simulation (AnalMode=1)? If so, I set：

TMax=630s, PCMode=1, RotSpeed=12.1, WaveMod=0(still water)，RdtnTMax=0

and
NREL 5.0 MW offshore baseline aerodynamic input properties; Compatible with AeroDyn v12.58.
SI SysUnits - System of units for used for input and output [must be SI for FAST] (unquoted string)
STEADY StallMod - Dynamic stall included [BEDDOES or STEADY] (unquoted string)
USE_CM UseCm - Use aerodynamic pitching moment model? [USE_CM or NO_CM] (unquoted string)
EQUIL InfModel - Inflow model [DYNIN or EQUIL] (unquoted string)
SWIRL IndModel - Induction-factor model [NONE or WAKE or SWIRL] (unquoted string)
0.005 AToler - Induction-factor tolerance (convergence criteria) (-)
PRANDtl TLModel - Tip-loss model (EQUIL only) [PRANDtl, GTECH, or NONE] (unquoted string)
PRANDtl HLModel - Hub-loss model (EQUIL only) [PRANdtl or NONE] (unquoted string)

and the .wnd is
!----------------------------------------------------------
! Time Wind Wind Vertical Horiz. Pwr.Law Lin.Vert. Gust
! Speed Dir Speed Shear Vert.Shr Shear Speed
!(sec) (m/s) (deg) (m/s) (m/s)
0.0 24 0.000 0.000 0.000 0.000 0.000 0.000

But the responses are shaking. In other words, the transient behavior is also exist, as shown below:

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无标题.png670×521 31.5 KB

So I can’t determin the steady-state value, what do you think? Wheather my parameters setting above is right?

2

Dear Yaqi,

Your input parameter settings sounds reasonable except that there is no reason to set RdtnTMax to 0 s (disabling wave radiation damping) when AnalMod is 1 (time marching simulation).

Because of features of the model such as gravity, shaft tilt, etc. you will never reach a point (no matter how long you run) where the simulation output is a fixed value for all channels. However, the results you’ve shown clearly show a periodic steady-state condition–were there is a small oscillation about a fixed mean. It is the mean value of this periodic steady-state condition that you can identify as an “effective” steady-state condition. You can quantify the mean value by taking a time-average of the periodic steady-state solution (say, over the last 200 s of the simulation). (This is why the FAST linearization process always produces a periodic steady-state solution as opposed to a time-invariant solution.)

I hope that helps.

Best regards,

3

Dear Jason,
Thank you for answering my question, it has been very helpful.

Best wishes!