Although standard codes are used by US turbine manufacturers to estimate the design loads of their turbines, the codes have not previously been accepted by European certifying agencies.

Through a partnership between the NREL and Germanischer Lloyd (GL) of Hamburg in Germany, recognised as the world's foremost certifying body for wind turbines, both FAST and ADAMS have been approved for design and certification calculation of onshore wind turbine loads.

The approval of the codes means the US turbine manufacturing sector no longer has to have turbines certified by re-evaluating designs using European codes or European consultants, saving considerable time and money.

The FAST code (for Fatigue, Aerodynamics, Structures, and Turbulence) is a comprehensive aeroelastic simulator capable of predicting extreme and fatigue loads of two and three bladed horizontal-axis wind turbines.

ADAMS (Automatic Dynamic Analysis of Mechanical Systems) is a general-purpose, multibody, dynamics code developed by MSC Software with unlimited degrees of freedom also used to provide stress modeling for robots, satellites and motor vehicles.

ADAMS is slower than FAST, but more versatile as FAST is limited to standard horizontal-axis wind turbines while ADAMS can model almost any kind of horizontal-axis wind turbine. Both require the AeroDyn subroutine library to model aerodynamics.

To gain acceptance of the codes, NREL and GL compared FAST, ADAMS, GL's DHAT, and Garrad Hassan's GH Bladed European codes by modelling two turbines.

Results of the comparison will be published in an NREL technical paper and presented by Marshall Buhl from NREL at the 2006 American Society of Mechanical Engineers' Wind Energy Symposium in Reno, Nevada.

In the report, GL said the test showed good agreement between the codes. GL has granted NREL a certificate for FAST and ADAMS, stating the codes could be considered suitable for the calculation of onshore wind turbine loads for design and certification according to European standards.