TurbSim Random Seeds

Discuss the effects of turbulence on wind turbines and its simulation.

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Timo.Strotbaum
Posts: 6
Joined: Mon Jun 04, 2018 10:18 am
Organization: RWTH Aachen
Location: Germany

TurbSim Random Seeds

Postby Timo.Strotbaum » Tue Jul 03, 2018 11:23 am

Hi,

I´m currently writing my Bachelor-Thesis about a multi body simulation of a wind power drive and therefore I need to create Full-Field turbulent wind files with TurbSim.
My next step would be to find out which value would be the best for the resolution (grid number points, 11x11, 21x21 ...).
So I created many FF files using the same fixed numbers in the TurbSim input file (line 1&2) and left everything else the same, except the number of grid points.
I was hoping that TurbSim would create exactly the same Wind Files, but the development of the wind speed differs in every file.

Am i doing something wrong, or is there no way to create the same wind file twice?

Thanks in advance,

Timo

Jason.Jonkman
Posts: 4858
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: TurbSim Random Seeds

Postby Jason.Jonkman » Wed Jul 04, 2018 3:40 am

Dear Timo,

Adding grid points in TurbSim will change how the internally generated random numbers are distributed between the various calculations. You can create the same wind file twice if you leave the random seeds unchanged and don't change the number of grid points or time/frequency resolution.

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov

Timo.Strotbaum
Posts: 6
Joined: Mon Jun 04, 2018 10:18 am
Organization: RWTH Aachen
Location: Germany

Re: TurbSim Random Seeds

Postby Timo.Strotbaum » Wed Jul 04, 2018 5:38 am

Dear Mr. Jonkman,

thank you for your very fast answer! that explains my problem.
So there is actually no way to make a detailled analysis of how many grid points are necessary to gain the best result? Has anyone ever made some research on this topic?

Best regards,

Timo

Jason.Jonkman
Posts: 4858
Joined: Thu Nov 03, 2005 4:38 pm
Location: Boulder, CO
Contact:

Re: TurbSim Random Seeds

Postby Jason.Jonkman » Thu Jul 05, 2018 12:21 am

Dear Timo,

The rule of thumb is to set the spatial discretization in TurbSim equal to the maximum chordlength of a blade (about 5 m for the NREL 5-MW turbine) and set a time step so as to have a frequency resolution that can excite all dominant structural modes (we typically set 0.05 s, but this may be finer than necessary for large multi-megawatt wind turbines).

To do such a convergence study yourself will require you to compare various resolutions statistically rather than via time series. As with a loads analysis, you'll need to run many simulations for a given wind condition (e.g. 10 seeds of 10-minute simulations per bin).

Best regards,
Jason Jonkman, Ph.D.
Senior Engineer | National Wind Technology Center (NWTC)

National Renewable Energy Laboratory (NREL)
15013 Denver West Parkway | Golden, CO 80401
+1 (303) 384 – 7026 | Fax: +1 (303) 384 – 6901
nwtc.nrel.gov


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