A system-based reduction method for spatial deformable multibody systems using global flexible modes

The most popular strategy to reduce the complexity of flexible multibody systems modeled using the Floating Frame of Reference Formulation (FFRF) is based on reduced-order models (ROM) derived through component modes. In this paper, we propose the use of global modes to build a feasible modal basis of reduction. The global modes are derived from the assembled system and satisfy the reference conditions necessary to prevent rigid-body motions inside the floating frames of the flexible components. Furthermore, the global modes are consistent with the constraints provided by the mechanical joints. As for the classic Component Mode Synthesis (CMS) methods, the proposed reduction pertains only to the elastic coordinates while the gross motion coordinates are kept in the final ROM. This approach allows for describing the deformation field of the whole mechanisms using linear combinations of global shapes. As a consequence, a reduced number of global modal intensities is required and the computational burden is significantly decreased compared to the unreduced model.