17. Uncertainty Propagation in Floating Raft System by FRF-Based Substructuring Method for Elastic Coupling

The FRF-based substructuring method considering elastic coupling is investigated for predicting vibration transmission and uncertainty propagation in floating raft system. The effects of various commonly encountered errors of substructure FRFs, such as pole shifting, reciprocity violation, negative imaginary part of driving-point FRFs, on the modeling results are investigated. The simulation results demonstrate that the noise on FRFs of raft can influence the assembly FRFs of base and raft; while, some kinds of noises cannot be propagated to the assembly FRFs of machines for the rigid machines are coupled through elastic isolators, bringing about impedance mismatch. The SVD cannot eliminate the studied noises. The uncertainty in substructure FRFs can be amplified due to the coupling process. Propagation of uncertainties of FRFs is quantified based on an analytical approximate moment method using the derivatives of substructure FRFs and variance defined on these parameters. The moment method is of high efficiency and accuracy compared with Monte Carlo probabilistic method.