Analysis Of Floating Raft Isolation System Based On SEA And FE-SEA Method

In the 1950 s and 1960 s, America began to use the floating raft technology in submarine, after decades' development, floating raft has been widely used especially in the marine field. As the development of the floating raft, there has been more and more structures of floating raft. Compound floating raft is a kind of complex and large raft, it is comprised of upper layer and lower layer, both layers can be used to install equipment and pipes.For structural vibration analysis, in low frequency, finite element method is used, in middle frequency, hybrid method is used, while in the high frequency, statistic energy analysis is adopted. In this paper, finite element method and statistic energy analysis are used to research the middle and high frequency vibration of floating raft.Based on the statistic energy analysis, the method of dividing subsystems is studied in this paper, the whole system is divided into raft subsystem, equipment subsystem and base subsystem. And the raft subsystem is divided into two kinds of subsystem: ribbed plate subsystem and uniform plate subsystem. After building the SEA model, vibration level difference is used as the evaluation of isolation effect to study the middle and high frequency isolation effort in different working conditions, and study the effect of coupling loss factor, damping loss factor and the structure of raft. It is found that coupling loss factor has the largest influence on the isolation effect.On the basis of SEA model, some subsystems which have lower modal density are meshed, and turned into FE subsystems, then the hybrid model is built. Analysis is done between 400 hz and 1250 hz. Compare the test results and calculation result of hybrid model and SEA model,it is found that as the frequency increases, the accuracy of SEA model increases to, and the hybrid model is more accurate in middle frequency.