Dear Mark,
The approach you propose to model blades with pre-bend may be fairly straightforward, but I question the accuracy you’d obtain from the result. Here are a couple things to consider:
*Built-in curvature and sweep in the blade will lead to coupling between flapwise and edgewise bending and torsion which would not be captured by the approach you propose.
*The FAST model has no rigid-body blade-pitch DOF. When the blade-pitch angles change because of commands from the pitch controller, because there is no blade-pitch DOF, there are no associated pitch rates or accelerations computed by FAST and the inertia, Coriolis, and other potential loads from the pitch motion will not be accounted for. The magnitude of these ignored terms will depend on how fast the blades pitch and on the degree to which the blades are precurved and preswept and on how much they deflect.
Issues such as these are what has kept us at NREL from adding a simple model for blades with pre-bend. The dynamics of a composite spinning blade with bending, torsion, pre-bend, and large deflection is quite compilicated, which is why it has taken a while for NREL to add these to FAST. However, NREL is working on introducing these features, as described in my Nov 26, 2012 post in the forum topic found here: Coupled blade modes in FAST.
Best regards,