Selection of normal and characteristic constraint modes in component mode synthesis

Criteria for the selection of substructure fixed interface normal modes and Reduced-Order-Model (ROM) characteristic constraint (CC) modes are discussed with regard to component mode synthesis. An extension of the Kammer and Triller's Effective Interface Mass (EIM) is presented as a means of determining the dynamic importance of CC-modes used in ROMs. The CC-mode transformation matrix is used to transform the EIM of each Craig-Bampton substructure comprising the ROM into CC-mode based coordinates. This transformation provides a measure of the dynamic interaction between CC-modes and the substructure normal modes. The extension is demonstrated on a cantilever plate model composed of two substructures and provides a means of quantitatively determining at what point higher CC-modes can be truncated in ROM synthesis. Resulting ROMs are compared for accuracy against the unreduced FEM and Craig-Bampton solutions. Results suggest the proposed extension provides an improved metric for determining the retained CC-modes in ROM reduction.