Modal Reduction of Fatigue Sensitive Components for Comprehensive Rotorcraft Dynamics Simulation

Rotorcrafts often involve fatigue sensitive components that present complex three dimensional geometries and undergo small deformations, such as a fuselage, a swashplate and pitch link rods. For those components, two questions must be answered: (1) what is the impact of the flexibility of the component on the dynamic response of the overall system and (2) what is the three-dimensional stress field in such component? The prediction of the three-dimensional stress fields in these complex components and the assessment of their fatigue life require the use of three-dimensional finite element models of the components. Nevertheless, the fine mesh sizes often necessary to capture complex geometries and intricate material property distributions result in a set of algebraic equations that is prohibitively large for direct dynamics simulation. In addition, geometric complexity does not imply a complex dynamic response of the structure, which can often be captured accurately by a small number modes whereas fine mesh sizes result in the appearance of spurious, high-frequency modes that are of little physical relevance.