Transient turbulent wind

Wind & Water Inflow Turbulence
1

Dear all,

I would like to know if it is possible to simulate transient turbulent wind conditions in OpenFAST. I would like to simulate a wind ramp followed by a turbulent wind (ntm) with 44 m/s mean wind speed at hub height.
I am running DLC 6.1 with this conditions (without the initial ramp, as I don’t know how to do it, or if it is possible in OpenFAST), and the initial transient of the simulation makes the platform overturn.

On the other hand, I would like to know how many frequency components the wave spectra of the simulations have, since this is not indicated in Hydrodyn theory manual.

Thanks in advance.

Best regards,

Nicolás

2

Dear Nicolás,

Normally turbulent wind conditions are simulated about a fixed mean wind speed; i.e. stationarity of the inflow turbulence is assumed. NREL has not provided an engineering tool to calculate the turbulent wind atop a wind ramp. A similar question was discussed fairly recently on this forum–see: Stitch Together TurbSim Timeseries.

HydroDyn computes the wave-elevation time series by performing an inverse FFT. The number of frequency components is determined by the wave time step (WaveDT), which determines the maximum frequency, and periodic length (WaveTMax), which determines the frequency step. This is described in the HydroDyn documentation, as well as in the comments to the right of inputs WaveTMax and WaveDT in the HydroDyn input file.

Best regards,

3

Dear Jason,

Thanks for the reply.
Reading the forum you indicated in the answer, I saw that it is possible to concatenate several TurbSim .bts files in a single OpenFAST simulation, but I don’t know how to do it.
If you can tell me the procedure to do that, or some document where it is explained, it would be very helpful.

Again, many thanks in advance.

Best regards,

Nicolás

4

Dear Nicolás,

I have not done this myself. I provided general guidance in the forum post linked above. I don’t think I can provide more general guidance then this.

Best regards,

5

Dear Jason,

I’ll try it on my own. In any case, thank you very much for your help.

Best regards,

Nicolás