FAST Revs Up with a v8
February 25, 2015
Offshore and land-based wind turbine systems are subject to complex and harsh operating conditions. When designing systems for such conditions, wind technology developers need powerful tools. One such tool is the computer-aided engineering tool called FAST, developed and supported by the National Renewable Energy Laboratory (NREL). The laboratory has recently released an improved and expanded version of FAST (FAST v8) that features a new modularization framework that boosts the tool’s power, robustness, and flexibility.
The framework contains modules for aerodynamics (AeroDyn); hydrodynamics for offshore systems (HydroDyn); control and electrical drive dynamics (ServoDyn); rotor, drivetrain, nacelle, tower, and platform structural dynamics (ElastoDyn); multimember substructure structural dynamics (SubDyn); mooring statics (MAP); and ice loads (IceFloe). The new framework also improves the ability to read, implement, and maintain source code; increases module sharing and shared code development across the wind community; improves numerical performance and robustness; and enhances flexibility and expandability to enable further developments of functionality without the need to recode established modules.
Aside from the framework, other specific software upgrades in FAST v8 include:
- An enhanced AeroDyn module that can simulate both the upwind and downwind influences of the wind turbine tower on the rotor and calculate the tower drag load
- The capability to analyze multimember offshore wind turbine substructures
- A new state-space hydrodynamic radiation theory option in the HydroDyn module
- The capability to include wave directional spreading and second-order hydrodynamic effects in the HydroDyn module
- A new MAP module for modeling multisegmented mooring quasi-static behaviors of floating offshore wind turbines.
The multimember offshore wind turbine module enables the software to model the hydrodynamic loading and structural dynamics of multimember, fixed-bottom offshore wind substructures such as tripods and jackets. These types of offshore wind structures are being built in water depths between 30 and 60 meters. The substructures can be composed of multiple interconnecting members with incline, and the members can accommodate the effects of flooding and marine growth.
The new state-space hydrodynamics option in HydroDyn enables more computationally efficient time-domain solutions for large platform hydrodynamic radiation than the previously available implementation, and permits model linearization that is important for modal analysis, linear system-based controls design, and linearized stability analysis.
The implementation of directional spreading and second-order hydrodynamic theory enables more accurate modeling of sea states and the associated wave-excitation loads on fixed-bottom and floating wind systems and was one of the top requests for HydroDyn improvement by the offshore wind engineering community.
MAP simulates the load versus displacement relationships of mooring systems composed of interconnected cables—a critical component of floating offshore wind systems.
NREL recently verified the new capabilities of FAST v8 to model fixed-bottom and floating offshore wind turbines. The laboratory analyzed a series of load cases with both wind and wave loads and compared the results against those from the previous international code comparison projects: the International Energy Agency (IEA) Wind Task 23 Subtask 2 Offshore Code Comparison Collaboration (OC3) and the IEA Wind Task 30 OC3 Continuation (OC4) projects. For more information, read Verification of the New FAST v8 Capabilities for the Modeling of Fixed-Bottom Offshore Wind Turbines and Verification of New Floating Capabilities in FAST v8.
Ongoing work to enhance FAST includes:
- An improvement of the aero-elastic capabilities for large aero-elastically tailored blades by an overhaul of the AeroDyn module and an introduction of the BeamDyn module, with validation against data from Siemens
- The introduction of a new interface to controls implementation through MATLAB/Simulink
- An expansion of floating functionality (nonlinear fluid-impulse hydrodynamic theory and lumped-mass- and finite-element-based mooring dynamics) and further validation (against computational fluid dynamics and through collaboration under the IEA Wind Task 30 OC4 with data Correlation (OC5) project)
- The completion of the new modularization framework (specifically operating-point determination and linearization of the full coupled system)
- Transition from an NREL-centric development to an open development-community environment.