GAROS

A program for the aeroelastic and rotordynamic analysis of wind turbines

GAROS is a program for the aeroelastic- and rotordynamic analysis of wind turbines. Stability and dynamic response analysis can be done. Both horizontal and vertical axis turbines can be analysed.

The program is based on a modal coupling method of tower and rotor. The structures are idealised by finite elements and the modes are calculated by the finite element program NX Nastran. The modal model contains the fully coupled rotor dynamic matrices. Also the geometric stiffness matrix is included. In the stability analysis the quasi steady linearized aerodynamic stiffness, damping and mass matrices are considered. The static deformation of the blades can be accounted for in order to calculate the stability behaviour for different operating conditions. Also the true unsteady aerodynamic forces including the Theodorsen function which describes the time lag between motion and force can be accounted for. In that case a non-linear iteration is applied for the solution of the complex eigenvalues. For rotors with two blades the eigenvalues are calculated by the Floquet method because the equations contain periodic terms.

In addition to the stability analysis, dynamic response analysis can also be done. In order to check the results of the stability analysis, a sweep with increasing rotor speed and wind velocity can be performed. Aerodynamic forces due to wind gradient, tower influence, oblique flow, gusts and turbulence can be accounted for. Centrifugal and gravity excitation forces are also included. The results can be plotted as function of time or as polar plots as function of rotor angle. Nodal displacements and element forces can be recovered. The aerodynamic induction factor can be accounted for horizontal axis rotors.