Question about rotating vs fixed frame inputs when using LinInputs = 2

Wind & Water Systems Engineering Software Tools
1

Dear OpenFAST community,

I am currently working with linear models generated using OpenFAST, and I’ve been experimenting with the option LinInputs = 2 to include additional inputs in the linearization. While analyzing the newly included inputs in the linearized models, I noticed that some of them related to the blades (particularly those related to AeroDyn) are marked as rotating frame = false in the .lin files.

I would like to understand whether there is a known limitation or incomplete implementation in the development of the linearization inputs when LinInputs = 2 is used, or I am misunderstanding the description and these inputs are in fact expressed in the fixed frame rather than the rotating blade frame.

Could someone clarify how the reference frame of these addtional inputs is defined when using LinInputs = 2?

Thank you very much for your help.

Best regards,

Daniel Lacheta.

2

Dear @Daniel.Lacheta,

The implementation of the RotFrame_u flag associated with each linearized system input perturbation is complete as far as know. The flag indicates whether the input perturbation is expressed globally (FALSE), or locally (TRUE), such that it should be transformed through a multi-blade-coordinate transformation (MBC) in post-processing. This flag is mostly used by the MBC3-based post-processors.

Note that some inputs on the blade are expressed globally, not locally, so, RotFrame_u is often FALSE even for input perturbations on a blade.

Best regards,

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