Drive train torsion output

Hi,

Is there a Drive-train torsion in Fast 7 as simulation output?
When the drive-train DOF is enabled for Linearization, torsion is one of the output states. So, in “.fst” file output section, what can we use to see one of these outputs? Drive-train torsion, Drive-train torsion ratio, Generator azimuth since this values must be related to each other.

Dear Elham,

Are you referring to the twist angle of the drivetrain? This angle is not directly output from FAST v7, but you can output the drivetrain azimuth angles at the hub (LSSTipPxa) and gearbox-end of the low-speed shaft (LSSGagPxa) and subtract one from the other to back-out the twist angle. (Watch out at 0 and 360 degrees because the azimuth angles are output with modulo arithmetic between 0 (inclusive) and 360 (exclusive).)

I hope that helps

Best regards,

Dear Jason,

Thank you very much for your quick reply.
Adding the low-speed shaft output (“LSSGagPxa”) works fine and gives me the output between 0 to 360 which seems to be correct. However, when I add “LSSTipPxa” to the output list, I get this error:

Output returned by S-function ‘FAST_SFunc’ in ‘NREL5MW_Reg3/FAST1/S-Function’ during flag=3 call must be a real vector of length 43
FAST_SFunc completed.

I checked the excel file ‘OutListParameters.xlsx’ and seems the name LSSTipPxa is correct. I also tried its other names like ‘LSSTipPxs’, ‘LSSTipP’ or ‘Azimuth’. Non worked. Is there anything that I am missing on the output name?

Dear Elham,

I’m not familiar with this error. Can you run the simulation again with:
DT_Out = “DEFAULT”
OutFileFmt = 1 (for text-based output)

Does the resulting data in the output file look reasonable up until the error (e.g. there are no invalid data e.g. NaNs in the file)?

Best regards,

Dear Jason,

The output file looks fine until I add “LSSTipPxa” to the output list in ‘.fst’ file. Seems like FAST 7 Matlab S-Function, treats this parameter as an invalid output name and crashes immediately when I run it. Then the generated output file is empty.
I tried to use other names such as ‘LSSTipPxs’, ‘LSSTipP’ or ‘Azimuth’ but I get the same error.
Is there any sample ‘.fst’ file which has already used “LSSTipPxa” so that I can check?

Best Regards

Dear Elham,

I don’t really understand why adding output LSSTipPxa would cause any problems in the FAST v7 MATLAB S-Function. What happens when add output LSSTipPxa and you run the FAST v7 executable instead of the MATLAB S-Function?

Best regards,

Dear Jason,

Thank you for your helps. Seems the last error was due to the Matlab version incompatibility. On my PC, FAST 7 is not very stable on Matlab 2017 but works fine with 2014. Also I can now read LSSTipPxa as well. Thanks alot!