Hybrid Modeling of Floating Raft System by FRF-Based Substructuring Method with Elastic Coupling

Abstract

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The FRF-based substructuring method with elastic coupling by using hybrid experimental and numerical FRFs and impedance is investigated for predicting vibration transmission in floating raft system. The floating raft system composed of one machine, upper and lower isolators, raft and base under symmetric and unsymmetrical excitation conditions is studied experimentally to show the influence of rotational Degrees of Freedom (DOFs). The results demonstrate that if the system is exposed to unsymmetrical excitation, the isolators will undergo bending deformation and it should consider the vibration transmission by rotational DOFs. For hybrid modeling, since measurement of FRFs is limited to some translational DOFs, FRFs of other DOFs are calculated by numerical methods. Three possible ways are proposed to improve the modeling accuracy. The identification method for mobility of isolators in rotational DOFs under static load is suggested. Filters constructed by piecewise linear interpolation method is used to condition the numerical FRFs with the measured FRFs. The truncated Singular Value Decomposition (SVD) approach is used to improve the quality of measured FRFs in the presence of measurement errors. Careful application of the proposed measures may result in better prediction.