Hi everyone, i have three doubts and i would really be grateful if you could help me with this:
-Is it valid to do a simulation of 200 seconds with a DT of 0,05? I would like to put 0,005 but since i have to copy the table of the output file, i want to make it condense. However, is there a problem with these numbers i said?
-About linearizing, what things could we obtain with it?
-I am doing a final thesis for the upscaling from 15 MW WT to a 20 MW, focusing only on the RNA and tower (not on the floating or fixed platform). Apart from running simulations for both turbines with steady wind (from 3 m/s to 25 m/s) and turbulent wind, would you recommend adding more interesting things to my final thesis which can be done with openfast? I know there are many thought-provoking things i could get with openfast , but what ones would you say it is a must in openfast?
Thanks
Dear @Alberto.Utrera,
Regarding your first question, as has been discussed before in several forum topics, the required time step (DT
) of an OpenFAST simulation is dictated by the natural frequencies and excitation frequencies inherent in a model. You can always coarsen the OpenFAST output (via input DTOut
) if you wish to have less output data than you’d get if you output every time step. The required length of a given simulation (TMax
) is typically chosen to cover the core dynamic response of the transient or to capture statistical significance (when accounting for turbulence). 10 minute simulations are typical for wind turbine simulations for a given turbulent condition.
Regarding linearization of OpenFAST, it is mainly useful for full-system eigenanalysis (to obtain full-system natural frequencies, damping, and mode shapes), controls design, stability analysis, and for generally “understanding” the system response.
Best regards,
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Thanks for the reply @Jason.Jonkman.
In which file, could I be able to see the highest natural frequency in Hz of coupling between modules?
In my simulation, I am using steady conditions and not turbulent. I am setting the Tmax to 200s. Although the trends of the majority of some parameters can be seen perfectly (because of the convergence), there are others that I do not know if the response will be damped or amplified. In this case, it is better for me to broaden the Tmax, right?
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Dear @Alberto.Utrera,
You can find the highest natural frequency (as well as any full-system natural frequency) through an OpenFAST linearization analysis, followed by Eigenanalysis. For the purposes of computed the highest frequency for identifying DT, you can choose simple conditions such as CompAero
= 0 (in the OpenFAST primary input file) and RotSpeed
= 0 (in ElastoDyn).
When using steady inflow, presumably your objective is to find the steady-state condition. If the steady-state condition is not obvious after 200 s, you could increase TMax
.
Best regards,