Analysis Flow for Changing Tower Dimensions

Wind & Water Computer-Aided Engineering Software Tools
1

I previously used FASTv7, but this time I’m using OpenFASTv4.2.0.
It’s been a while since I last did this, so I’d like to confirm the analysis flow and see what steps are required when the tower dimensions, etc. are changed.

① Change input files such as tower.dat and perform linearization analysis.

② Calculate the RNA mass inertia matrix using the parallel axis theorem for the 6x6 mass matrix.

③ Input the obtained data and find the eigenvalues ​​and eigenmodes using BModes.

④ Enter the data into ModeShapePolyFitting.xls to obtain the mode coefficients.

I also have four questions.

  • In which output file is the mass matrix (6x6) obtained in ① stored?

  • Have any changes been made to the analysis flow for steps ① through ④ between FASTv7 and OpenFASTv4-2-0?

  • Could you please tell me how to calculate HubIner and NacIner? (I want to change the weight of the hub and nacelle, so I’d like to recalculate.)

-Is there a way to calculate the mass-inertia matrix of the RNA without using the parallel axis theorem or something like that?

2

Dear @Kazuya.Nishiyama,

The overall approach to updating the tower properties-including the geometry, mass, stiffness, and mode shapes–should be very similar between FAST v7 and OpenFAST, with the biggest difference being in how you calculate the RNA mass, center of mass, and inertias through a linearization analysis. The linearization process to extract the 6x6 mass matrix of the RNA is a bit different between FAST v7 and OpenFAST, as discussed in the following forum topic: OpenFast 2nd order Linearization. Of course, the RNA properties wouldn’t change if you only changed the tower.

Regarding HubIner, this should be the hub inertia about the rotor axis. Similarly, NacYIner should be the inertia of the nacelle (including the generator, gearbox, and drivetrain, minus the rotor) about the nacelle-yaw axis.

Best regards,