Allow separate teeter inertia for 2-bladed turbines

[abhineet-gupta]

Feature or improvement description
OpenFAST assumes that hub for a two-bladed turbine is a rod and the hub-inertia about the rotor axis and the teeter axis is the same. This PR addresses this shortcoming allowing users to provide the two inertia's separate.
Computation for three-bladed turbines are not affected.

Related issue, if one exists

Impacted areas of the software
ElastoDyn

Additional supporting information

Test results, if applicable

[andrew-platt]

I'll look at the history - there may be something missing in the regression test branch (missing merge).

[andrew-platt]

• merge r-test branch with this PR merge

[abhineet-gupta]

This PR changes the computation for 2 bladed turbines slightly.
Previous imlementation for 2-bladed turbines:

      p%Hubg1Iner = ( InputFileData%HubIner - p%HubMass*( ( p%UndSling - p%HubCM )**2 ) )/( p%CosDel3**2 )
      p%Hubg2Iner = p%Hubg1Iner

Implemention in this PR:

      p%Hubf1Iner = InputFileData%HubIner
      p%Hubf2Iner = InputFileData%HubIner_Teeter - p%HubMass*( ( p%UndSling - p%HubCM )**2 )

Note that we have switched from g-axes to f-axes for hub inertia in rest of the code.

The following plots demonstrate this findings.
Two bladed turbine: AWT_YFix_WSt

Zoomed in:

Labels:
Bak = Plot from outb in the r-test repo
Run = Plot from running the build from this PR
Dev = Plot from runnign the build from dev branch

For a 3-bladed turbine, as f and g axes are same and the implmentation remains the same:

      p%Hubf1Iner = InputFileData%HubIner
      p%Hubf2Iner = 0.0

These tests should pass.

If you both (@andrew-platt , @jjonkman ) agree with the code changes in the PR, I can upload new .outb files to the few test that are failing.

Abhineet

[abhineet-gupta]

As the definition of inputs change with this PR, I have updated the r-test ElastoDyn files with new values for HubIner and HubIner_Teeter to match the turbine. The tests pass now.

PS: This PR also has contributions from @faisal-bhuiyan.

[jjonkman]

Thanks for making this change. See a couple minor comments below.