offshore wind spectral model

Hi all,

Is there any offshore wind spectral model that can use the diabatic logarithmic wind profile option in Turbsim?

Thanks
Ashenafi

You can use the “LOG” [diabatic (logarithmic)] profile type with any of the spectral models in TurbSim.

TurbSim doesn’t have any specific offshore spectral models, but typically people use the IEC Kaimal model for offshore conditions. The Kaimal model assumes RICH_NO is 0, so the equation for the LOG profile is simplified a bit. You can also specify user-defined wind profiles and user-defined spectra if you use the TurbSim v2.0 alpha version.

Thank you Bonnie. I appreciate your help. I am closer to getting what I am looking for. I just need few more things to check.

For me using IEC Kaimal model for offshore conditions would have made things easier. the only problem is I will be simulating offshore wind at different atmospheric stability conditions by varying the RICH_NO. and wind profiles. Obtaining offshore user-defined spectra for different stability condition is also not quite straight forward for me.
It looks the User Defined Time series option is the best option I have. here is what I want to check:
on TurbSim alpha version, on the Time Series Input File (TurbSim User’s Guide v2.00.00, appendix A, Figure A-2), the data v, w, and u components listed for 600 seconds from sonic anemometers, are they direct measurements made every 0.05 seconds as presented in this input file or are they obtained from average wind speed data say 10min average?
I am using offshore data from Egmond aan zee wind farm and they are 10min average data. I just want to check if they can be of any use.

Best regards
Ashenafi

Also in one forum discussion,[url]http://forums.nrel.gov/t/user-defined-shear-profile/613/1], you mentioned about a user defined Kaimal Spectra for 12 m/s winds at 90 m hub height.http://wind.nrel.gov/public/bjonkman/Samples/UsrSpec.inp.
can this user defined kaimal spectra be used with out change, for other hub height wind speeds, by only changing the hub height wind speed from the Meteorological Boundary Conditions at the TurbSim input file?

Best regards
Ashenafi

If you have only 10-min average data, I wouldn’t recommend using the time-series input file. The time series output from TurbSim is going to contain only the times you enter.

From what you have described, it seems to me you could use the IECKAI model with a user-defined wind profile, which is based on RICH_NO. You could also use the user-defined spectra model set up for the Kaimal model and then ask for the LOG wind profile. You will want to make sure that the coherence is set properly, too. There are sample input files for each of these user-defined options in the TurbSim v2.0 CertTest folder (UsrShear.inp and TurbSim_UsrSpec.inp). The spectra in the UsrSpec.inp file are just the values defined by the Kaimal PSD equation from the IEC standard. This equation depends on the mean wind speed, hub height, and desired standard deviation (turbulence intensity), so you will have to modify it if any of those values change. You can use the SpecScale* parameters at the top to get different standard deviations, but you will need to regenerate the table for changes to mean wind speed or hub height.

Please do keep in mind, though, that the IECKAI assumes RICH_NO = 0. Atmospheric stability will also influence the spectral shape, so by mixing and matching what RICH_NO affects, you may have an unphysical model.

Thank you so much !!!