OpenFAST is a wind turbine simulation tool which builds on FAST v8. FAST.Farm extends the capability of OpenFAST to simulate multi-turbine wind farms. They were created with the goal of being community models developed and used by research laboratories, academia, and industry. They are managed by a dedicated team at the National Renewable Energy Lab. Our objective is to ensure that OpenFAST and FAST.Farm are sustainable software that are well tested and well documented. If you'd like to contribute, see the Developer Documentation and any open GitHub issues with the Help Wanted tag.

OpenFAST is under active development.

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

FAST v8, now OpenFAST, is a physics-based engineering tool for simulating the coupled dynamic response of wind turbines. OpenFAST joins aerodynamics models, hydrodynamics models for 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 the analysis of a range of wind turbine configurations, including two- or three-blade horizontal-axis rotor, pitch or stall regulation, rigid or teetering hub, upwind or downwind rotor, and lattice or tubular tower. The wind turbine can be modeled on land or offshore on fixed-bottom or floating substructures. OpenFAST is based on advanced engineering models derived from fundamental laws, but with appropriate simplifications and assumptions, and supplemented where applicable with computational solutions and test data.

With OpenFAST, you can run large numbers of nonlinear time-domain simulations in approximately real time to enable standards-based loads analysis for predicting wind system ultimate and fatigue loads. You can also linearize the underlying nonlinear model about an operating point to understand the system response and 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-wake effects and blade-element aerodynamic loads, including dynamic stall. The hydrodynamics models simulate the regular or irregular incident waves and currents and solve for the hydrostatic, radiation, diffraction, and viscous loads on the offshore substructure. The control and electrical system models simulate the controller logic, sensors, and actuators of the blade-pitch, generator-torque, nacelle-yaw, and other control devices, as well as the generator and power-converter components of the electrical drive. The structural-dynamics models apply the control and electrical system reactions, apply the aerodynamic and hydrodynamic loads, adds gravitational loads, and simulate the elasticity of the rotor, drivetrain, and support structure. Coupling between all models is achieved through a modular interface and coupler (glue code).

FAST.Farm extends the capabilities of OpenFAST to provide physics-based engineering simulation of multi-turbine land-based, fixed-bottom offshore, and floating offshore wind farms. With FAST.Farm, you can simulate each wind turbine in the farm with an OpenFAST model and capture the relevant physics 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 efficiency through parallelization to enable loads analysis for predicting the ultimate and fatigue loads of each wind turbine in the farm.

The full documentation is available at https://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 version of OpenFAST. Readthedocs hosts the following versions of the documentation:

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

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

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

• main
• dev

The main branch is stable, well tested, and represents the most up to date released versions of OpenFAST and FAST.Farm. The latest commit on main contains a tag with version info and brief release notes. The tag history can be obtained with the git tag command and viewed in more detail on GitHub Releases. For general use, the main branch is highly recommended.

The dev branch is generally stable and tested, but not static. It contains new features, bug fixes, and documentation updates that have not been compiled into a production release. Before proceeding with new development, it is recommended to explore the dev branch. This branch is updated regularly through pull requests, so be sure to git fetch often and check outstanding 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/
• https://nvie.com/posts/a-successful-git-branching-model/

Details for compiling compiling, using, and developing OpenFAST and FAST.Farm on Unix-based and Windows machines are available at readthedocs.

Please use GitHub Issues to:

• ask usage questions
• report bugs
• request code enhancements

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

OpenFAST and FAST.Farm are maintained and developed by researchers and software engineers at the National Renewable Energy Laboratory (NREL), with support from the US Department of Energy's Wind Energy Technology Office. NREL gratefully acknowledges development contributions from the following organizations:

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