Structural Dynamic Behavior of Wind Turbines - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 637

NASTRAN Finite Element Modeling
The general-purpose structural analysis code NASTRAN is the software commonly used
for modeling a wind turbine in finite elements to determine its natural vibration modes.
Before presenting an example of the modeling, a short description of the NASTRAN calcu-
lational procedure is in order, as it is applied to this specific problem. Two of the available
NASTRAN rigid format options are used in the modeling effort. First, a static analysis
with geometric stiffening effects is performed on the model under the action of centrifugal,
gravitational, and boundary forces. The resulting modified stiffness matrix ( K + K G in Eq.
(11-43)) is then retained via a modest amount of DMAP programming for use in the
subsequent complex eigenvalue analysis (the second rigid format).
NASTRAN users are provided with a choice of several complex eigensolvers. One
employs the upper-Hessenberg method and is very efficient. A method that has been used
successfully for the modal analysis of wind turbines is to first model the structure with the
necessary number of degrees of freedom, then use a standard Guyan reduction procedure
(also a NASTRAN option) to reduce the degrees of freedom to a manageable number
(approximately 100) and then apply the upper-Hessenberg method.