Enable modeling of floating MHK turbines

[hkross]

This pull request is ready to be merged.

Development is complete, documentation has been updated, and all regression tests pass. A new floating MHK regression test has been added. A corresponding r-test branch is on the OpenFAST/r-test repository.

Feature or improvement description

This pull request allows floating MHK turbines to be modeled by allowing the tower, hub, nacelle, and rotor to be defined below the platform and below the MSL. For fixed and floating MHK turbines, the coordinate systems remain unchanged from those used for wind turbines. However, the geometry for fixed MHK turbines is defined relative to the seabed and for floating MHK turbines is defined relative to the MSL. InflowWind values are defined relative to the seabed for both fixed and floating MHK turbines.

Impacted areas of the software

• AeroDyn module
• AeroDyn driver
• ElastoDyn module
• OpenFAST glue code

Test results

All regression tests have been updated and pass. A new floating MHK regression test has been added.

Check list

• Add new floating MHK regression test and baselines

[andrew-platt]

I know you have done extensive testing with on this feature, particularly with flipping the tower in ED. Could you include a couple of plots of the testing here for future reference?

[andrew-platt]

There was a conflict after merging #1543. I resolved this with two commits.

[ebranlard]

I approve this pull request, it tracks the change of tower heights and water level throughout the modules.

I have few random comments that are mostly personnal preferences and open to discussion, so they might be safe to discard :)

[ebranlard]

I'm not in favor of binary files added to the repo..

[hkross]

This was added to the AeroDyn documentation here (https://openfast.readthedocs.io/en/main/source/user/aerodyn/index.html), along with several other reference documents. I did not add it originally but noticed that it was not the most recent version, so just replaced it with the current version.

[jjonkman]

I don't disagree, but until all of these Word documents get ported over to readthedocs, I'd prefer the Word docs get shared. Having Word documentation is better than no documentation!

[hkross]

To check the accuracy of changes made to OpenFAST to allow floating MHK turbines to be modeled with the tower and RNA below the platform, simulations were run with land-based wind turbine example cases. Comparisons were made between the original definitions of these turbines and definitions in which all components were below ground (i.e., assigned negative Z coordinates). To ensure both definitions were equivalent, a steady and uniform inflow was used, shaft tilt was set to zero, tower shadow effects were neglected, and gravity was negative for the "upside down" case. Several outputs for the 5MW_Land_BD_DLL_WTurb r-test run this way are plotted here. Note that the upside down case of TwrBsFyt is plotted as negative to show agreement. It is expected that this output will be equal and opposite.

[hkross]

@andrew-platt I have addressed all comments, and it should be good to go. I am not sure why one of the FF tests is now failing.