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,
1 Like
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?
br
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,