I have a somewhat ‘historical’ question …
Why was torsional deformation of the blades never taken into account at FAST v7 ?
Shouldn’t twist modification be the most important DOF in terms of importance for the aerodynamic forces on the blade ?
Extending the structural formulation of FAST v7 to include an accurate torsion DOF is a nontrivial task and was never pursued by NREL. Instead, we put our efforts into developing the modularization framework of FAST v8 and the new BeamDyn blade structural dynamics module, which includes torsion (amongst other features).
how did you ensure validity of results generated with FAST v7 then ?
The turbine power output depends, of course, to a large extent on the bending deformation of the blades because the rotor diameter is altered … but isn’t induced twist a major influence for the aerodynamic forces on the blade and hence the deformations - especially when considering bend-twist coupling in the blades ?
FAST v7 was not applicable to blades with bend-twist coupling. When FAST was originally developed, most blades were designed to be quite stiff in torsion. It is only recently with modern wind turbines that blades have been made soft in torsion, and of course, FAST had to be further developed to support this evolution in blade design.