Define the "white noise"

Wind & Water Computer-Aided Engineering Software Tools
1

Dear All,

I‘m building a model about the 5MW Offshore Floating Wind Turbine , but now I wonder how to define the “white noise” in the simulation .There is given a .dat named

as you can see part of its data in the attachment , what confused me is how to use it or call it in my simulation , I never find some documents or directions about it .

Thank you for your time and help .

Wenbin
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2

Dear Wenbin,

White noise implies constant energy across all (or a banded range of) frequencies. We are adding a default option for generarting banded white noise waves in the next release of HydroDyn.

The “BandedWhiteNoise_DFT.dat” file you refer to was a data file we generated for use in the IEA Wind Task 30 OC4 project. Are you asking how to generate white noise in general or how to use the “BandedWhiteNoise_DFT.dat” file within FAST?

Best regards,

3

Dear Jason,

Thanks for your kindly reply . I am so sorry to make the question so puzzling.

My question is how to use the “BandedWhiteNoise_DFT.dat” file within FAST .

Best regards.

4

Dear Wenbin,

The “BandedWhiteNoise_DFT.dat” file was created with a slightly customized version of FAST and to use the “BandedWhiteNoise_DFT.dat” file will require a slight customization of FAST. To create “BandedWhiteNoise_DFT.dat”, we created a very simple user-defined wave spectrum routine (UserWaveSpctrm) to specify constant energy over a given frequency band. This spectrum, together with white noise, is used within FAST’s HydroCalc.f90 source file to calcululate the Discrete Fourier Transform (DFT) of the wave elevation; an Inverse DFT (IDFT) is then used to derive the wave-elevation time history. The DFT of the wave elevation at the intersection of the still water level and the undisplaced tower centerline is stored as variable WaveElevC0 in FAST’s HydroCalc.f90 source file. To create “BandedWhiteNoise_DFT.dat,” we simply output the REAL and IMAG components of WaveElevC0 to a file (along with the corresponding frequency (variable Omega) and wave number (variable WaveNmbr). To use “BandedWhiteNoise_DFT.dat” you would have to customize FAST to read-in and use the DFT stored in the file in place of the values of WaveElevC0 calculated internally within FAST’s HydroCalc.f90 source file.

I hope that helps.

Best regards,