Bladknik

Within the 'Bladknik' project new method for Buckling load prediction are develop for the FOCUS design package.

FOCUS

Focus was initially developed by WMC and contains wind turbine analysis programs of ECN. Focus is used for years by a large number of rotor blade and turbine manufacturers. The Focus package contains a detailed structural model of the rotor blade in terms of material layers defined similar as in the construction of a rotor blad, see graph ?. In addition to strength and fatigue analysis Focus was recently improved with regard to stability ('buckling') analysis tools developed in the Dutch Bladknik project [ECN-C-05-103].

Buckling load analyses

Rotor blade buckling invloves bending in flat and edge direction and also torsion and shear. The load combination that is most critical for buckling may be selected from several load cases in the design load set. For this purpose the Panel-based methods in Focus apply. If the most critical loading is found, more detailed analyses can be performed with FINSTRIP or with a FEM package such as ANSYS.

Panel-based methods

Fast, so suitable for searching the critical loading in a load-set. Influence of blade bending, torsion, and shear included. Improved for buckling of sandwich panels (shear web).

FINSTRIP for cross sections

Based on beam-theory, but includes the full structural integrity within a blade cross section. Integrated in Focus. Improved for asymmetric layup (still orthotropic). Faster eigenvalue solver included.

Interface to FEM package

FEM analyses have the most detailed structural representation, but require many CPU and effort to build an input model. FEM model can be generated with Focus. Option for ANSYS element SHELL181 (accepted by GL).