Vibration and power flow analysis of a vehicle structure using characteristic constraint modes

When the finite element model of a complex structure is partitioned into substructures in order to enable component mode synthesis, the reduced order model obtained from the Craig-Bampton method often features a large number of interface degrees of freedom (DOF). The authors have recently developed a method to reduce the interface DOF by using a set of so-called characteristic constraint (CC) modes. The resultant, highly compact CC-mode-based reduced order model provides a good platform to calculate the power flow between substructures. In this paper, the CC-mode method is applied to the finite element model of a vehicle structure with about 1.5 million DOF. A convergence study is conducted to find optimal mode selection criteria, and a 2124 DOF reduced order model is obtained for the 0-200 Hz range by using the CC-mode method. Then, a forced response analysis is carried out to verify its accuracy for capturing dynamic response, and a power flow analysis is carried out to demonstrate its capability for identifying critical power flow paths. A novel presentation method is adopted to display power flow through the vehicle structure as a two-dimensional "map". From the power flow maps, the structural paths through which the vibration energy is transmitted from the source to the key response points are clearly illustrated.