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OpenFAST is a wind turbine simulation tool which builds on FAST v8. FAST.Farmextends the capability of OpenFAST to simulate multi-turbine wind farms. They werecreated with the goal of being community models developed and used by researchlaboratories, academia, and industry. They are managed by a dedicated team at theNational Renewable Energy Lab. Our objective is to ensure that OpenFAST and FAST.Farmare sustainable software that are well tested and well documented. If you'd liketo contribute, see theDeveloper Documentationand any open GitHub issues with theHelp Wantedtag.

OpenFAST is under active development.

The transition from FAST v8 to OpenFAST represents the effort to bettersupport an open-source developer community around FAST-based aero-hydro-servo-elastic engineering models of wind-turbines and wind-plants. OpenFAST is thenext generation of FAST analysis tools. More information is available in thetransition notes.

FAST v8, now OpenFAST, is a physics-based engineering tool for simulating the coupled dynamicresponse of wind turbines. OpenFAST joins aerodynamics models, hydrodynamics modelsfor offshore structures, control and electrical system (servo) dynamics models,and structural (elastic) dynamics models to enable coupled nonlinear aero-hydro-servo-elastic simulation in the time domain. The OpenFAST tool enables theanalysis of a range of wind turbine configurations, including two- orthree-blade horizontal-axis rotor, pitch or stall regulation, rigid orteetering hub, upwind or downwind rotor, and lattice or tubular tower. The windturbine can be modeled on land or offshore on fixed-bottom or floatingsubstructures. OpenFAST is based on advanced engineering models derived fromfundamental laws, but with appropriate simplifications and assumptions, andsupplemented where applicable with computational solutions and test data.

With OpenFAST, you can run large numbers of nonlinear time-domain simulationsin approximately real time to enable standards-based loads analysis for predictingwind system ultimate and fatigue loads. You can also linearize the underlyingnonlinear model about an operating point to understand the system responseand enable the calculation of natural frequencies, damping, and mode shapes;the design of controllers, and analysis of aero-elastic instabilities.

The aerodynamic models use wind-inflow data and solve for the rotor-wakeeffects and blade-element aerodynamic loads, including dynamic stall. Thehydrodynamics models simulate the regular or irregular incident waves andcurrents and solve for the hydrostatic, radiation, diffraction, and viscousloads on the offshore substructure. The control and electrical system modelssimulate the controller logic, sensors, and actuators of the blade-pitch,generator-torque, nacelle-yaw, and other control devices, as well as thegenerator and power-converter components of the electrical drive. Thestructural-dynamics models apply the control and electrical systemreactions, apply the aerodynamic and hydrodynamic loads, adds gravitationalloads, and simulate the elasticity of the rotor, drivetrain, and supportstructure. Coupling between all models is achieved through a modularinterface and coupler (glue code).

FAST.Farm extends the capabilities of OpenFAST to provide physics-basedengineering simulation of multi-turbine land-based, fixed-bottom offshore,and floating offshore wind farms. With FAST.Farm, you can simulate each windturbine in the farm with an OpenFAST model and capture the relevantphysics for prediction of wind farm power performance and structural loads,including wind farm-wide ambient wind, super controller, and wake advection,meandering, and merging. FAST.Farm maintains computational efficiencythrough parallelization to enable loads analysis for predicting the ultimateand fatigue loads of each wind turbine in the farm.

The full documentation is available athttp://openfast.readthedocs.io/.

This documentation is stored and maintained alongside the source code.It is compiled into HTML with Sphinx and is tied to a particular versionof OpenFAST.Readthedocs hosts the followingversions of the documentation:

• latest - The latest commit on themain branch
• stable - Corresponds to the last tagged release
• dev - The latest commit on thedev branch

These can be toggled with thev: latest button in the lower left corner ofthe docs site.

OpenFAST and FAST.Farm are hosted entirely on GitHub so you are in theright place!The repository is structured with two branches following the"git-flow" convention:

• main
• dev

Themain branch is stable, well tested, and represents the most up todate released versions of OpenFAST and FAST.Farm. The latest commit onmaincontains a tag with version info and brief release notes. The tag history can beobtained with thegit tag command and viewed in more detail onGitHub Releases. For generaluse, themain branch is highly recommended.

Thedev branch is generally stable and tested, but not static. It containsnew features, bug fixes, and documentation updates that have not been compiledinto a production release. Before proceeding with new development, it isrecommended to explore thedev branch. This branch is updated regularlythrough pull requests, so be sure togit fetch often and checkoutstanding pull requests.

For those not familiar with git and GitHub, there are many resources:

• https://guides.github.com
• https://try.github.io
• https://help.github.com/categories/bootcamp/
• https://desktop.github.com/
• http://nvie.com/posts/a-successful-git-branching-model/

Details for compilingcompiling,using, anddevelopingOpenFAST and FAST.Farm on Unix-based and Windows machines are available atreadthedocs.

Please useGitHub Issues to:

• ask usage questions
• report bugs
• request code enhancements

Users and developers may also be interested in the NREL National WindTechnology Center (NWTC)phpBB Forum,which is still maintained and has a long history of FAST-related questionsand answers.

OpenFAST and FAST.Farm are maintained and developed by researchers and softwareengineers at theNational Renewable Energy Laboratory(NREL), with support from the US Department of Energy's Wind Energy TechnologyOffice. NREL gratefully acknowledges development contributions from the followingorganizations:

• Envision Energy USA, Ltd
• Brigham Young University
• The University of Massachusetts
• Intel® Parallel Computing Center (IPCC)