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An aeroelastic computer-aided engineering (CAE) tool for horizontal axis wind turbines
by Jason Jonkman, Ph.D.
National Wind Technology Center
NREL has sponsored the development, verification, and validation of various computer-aided engineering (CAE) tools for prediction of wind-turbine loads and responses. A streamlined CAE tool was developed through a subcontract between NREL and Oregon State University. This tool, called FAST, can be used to model both two- and three-bladed, horizontal-axis wind turbines.
The FAST code models the wind turbine as a combination of rigid and flexible bodies. For example, two-bladed, teetering-hub turbines are modeled as four rigid bodies and four flexible ones. The rigid bodies are the earth, nacelle, hub, and optional tip brakes (point masses). The flexible bodies include blades, tower, and drive shaft. The model connects these bodies with several DOFs. These include tower bending, blade bending, nacelle yaw, rotor teeter, rotor speed, and drive shaft torsional flexibility. The flexible tower has two modes each in the fore-aft and side-to-side directions. The flexible blades have two flapwise modes and one edgewise mode per blade. One can turn these DOFs on or off individually in the analysis by simply setting a switch in the input data file.
FAST uses Kane's method to set up equations of motion, which are solved by numerical integration. The implemented method makes direct use of the generalized coordinates, eliminating the need for separate constraint equations. FAST uses the AeroDyn subroutine package developed by Windward Engineering to generate aerodynamic forces along the blade.
FAST is extensively documented in the FAST User's Guide . Please refer to it for details on the use of the program. Jason Jonkman is writing a detailed theory manual that we hope to publish.
In 2002, Jason Jonkman and Marshall Buhl rewrote most of the code in modern Fortran. Marshall Buhl merged the formerly separate executables for two- and three- bladed turbines and rewrote most of the I/O for the program. Jason Jonkman rederived the fundamental equations and coded them using matrix manipulation routines instead of the original method of working directly with the individual elements of the matrices. This has allowed him to easily add new degrees of freedom (DOFs). Dr. David Laino of Windward Engineering made the changes necessary to interface the structural parts of FAST with the AeroDyn 12 aerodynamic routines.
In 2003, additional features were added to the code, including the ability to develop periodic linearized state matrices for controls design and the ability to use FAST as a preprocessor for generating MSC.ADAMS® datasets of wind turbine models. Aeroacoustic noise prediction algorithms were also introduced.
In 2004 several more features were added to the code, including a lateral offset and skew angle of the rotor shaft, rotor-furling, tail-furling, tail inertia and aerodynamics, yaw control, and high-speed shaft (HSS) brake control. An interface was developed between FAST and a master controller implemented as a dynamic-link-library (DLL) in the style of GH Bladed wind turbine software. An interface between FAST and Simulink® with MATLAB® was also developed, enabling users to implement advanced turbine controls in Simulink's convenient block diagram form.
Additional features were added to the FAST code again in 2005. These included new nacelle inertial measurement unit and tower strain gage outputs, upgrades to the simple variable-speed control model, and new support platform motion and loading functionality. Despite the addition of six new platform motion degrees of freedom, the code was also optimized so that it ran 15% faster than previous versions (or faster, depending on the options being modeled).
In 2010, FAST was updated to link with NWTC Subroutine Library and the updated AeroDyn v13.00.00 interface. New outputs were added in 2012, and in 2013 the ability to write FAST output in binary form was introduced. An interface between FAST and LabVIEW™ was developed, enabling FAST to be integrated into LabVIEW programs, including real-time applications.
To verify FAST, we compared it to MSC.ADAMS using several different turbine models and many different conditions, and we got very good agreement. We created test procedures that run 17 cases of FAST, and we plot the results of a recently changed FAST against MSC.ADAMS results and results from the previous versions of FAST and MSC.ADAMS. These test procedures are included in the FAST archive.
We are currently converting FAST to a new Modularization Framework. For the most recent alpha version of FAST, developed under this framework, please see the FAST (Modularization Framework) web site.
You may download the following files from our server:
If you want to refer to the FAST website in a report, here is a reference you can use:
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