Adding documentation for typical usages of OpenFAST

[ebranlard]

Feature or improvement description

Slight restructuring of the documentation:

1. Adding a section "Working with OpenFAST" as a "quick start", high up in the table of content. I've added a "Minimal Example" to the r-test (in dev right now, so links will fail) that the users can download for their first OpenFAST simulation.
2. Putting the "Testing OpenFAST" section further down in the table of content. I think our test suite is not for the basic user.
3. Moving all the modules documentation one level up so that the table of content is more readable.

The "Working With OpenFAST" section intend to describe some of the typical use cases of OpenFAST and point the users to the tools and scripts that can be used.
Some of these use cases are:

• running a simple OpenFAST simulation
• visualizing inputs and outputs data
• reading and writing files
• performing linearization
• running a suite of Design load cases
• running a parametric and combined cases
• postprocessing tools (links to the nwtc portal)

Impacted areas of the software

Documentation only

Live version
https://ebranlard-openfast.readthedocs.io/en/doc/source/working.html

• Address reviewers comments

[bjonkman]

1. I am not sure I believe this: "For a typical use case the linearization is done at only one time". If the rotor is spinning, you need azimuth-averaged values, and we typically do 36 linearization times (i.e., about every 10 degrees)
2. BeamDyn is included in the system-level linearization., so you should remove it from the section "options not yet supported with the linearization"
3. There is a typo on line 55: whre

[ebranlard]

Thanks @bjonkman for your input. I'll try to correct it soon.

[rafmudaf]

@ebranlard I think this info would be great and may fit in better in the upcoming OpenFAST user's guide: https://raf-openfast.readthedocs.io/en/docs-fast8readme/source/user/openfast/running_openfast.html

This is in my fork at https://github.com/rafmudaf/openfast/tree/docs/fast8readme.

[rafmudaf]

@ebranlard I'm closing this pull request, see the comment above!

[ebranlard]

I'm bringing this pull request back to life, to try to give a reference for some of the issues that are raised by the users (how to run cases, how to visualize outputs, how to troubleshoot cases, how to run linearization, etc.).
I've flushed out some more help and usage in my latest commit. I don't think that what I wrote is complete, but i think it's good to have a placeholder, something we can improve on with time, and send a link to users.

I think it qualifies as a section on its own, to give it more visibility, and since the user manual is already quite large..

I'm open to inputs and contributions :)

A live version is there :
https://ebranlard-openfast.readthedocs.io/en/doc/source/working.html

I think a tutorial and a set of working files (stored in the r-test in a standalone folder), could be great.

[ebranlard]

I believe this is now ready for review. I'm happy to receive comments and address what I can. I would be in favor in merging this as early as possible and having others take over if they want changes or updates :)

[jjonkman]

Thanks for adding this version useful user documentation! Hopefully this will reduce the number of beginner questions that often arise.