Design And Vibration Isolation Characetersitcs Research Of A Floating Raft Construceted With Periodic Structures

Floating raft systems connect marine power machinery with hull structures, and their dynamic characteristics are very important to the control of vibration and noise of marine ships. Power machinery, raft systems and hull structures are elastically coupled. If raft systems are not well designed, vibration isolation performance cannot be guaranteed and strong vibration and noise will be generated in hull structures, which will affect sound stealth characteristics as well as the safety of submarines. As a result, it is very important to design raft systems with high vibration/sound proof performance.This research comes from a national 973 project on vibration and noise control in marine ships. On the basis of a thorough review of existing researches, this thesis employs mainly numerical simulation to design new types of raft systems constructed from periodic structures. Six chapters are included and they are organized as follows.In Chapter 1, presented at first is the background of this research and then the review of literature about periodic structures as well as the design of rafts. Vibration characteristics of periodic structures are investigated in Chapter 2.Utilizing the Wave Finite Element (WFE) and the Substructure Recursive Synthesis method, the dynamic characteristics of some simple periodic structures are analyzed and verified by analytical and FEA results. The aim of this chapter is to find out an appropriate simulation method for rafts of periodic structure.In Chapter 3, new types of rafts are proposed and their band-gap characteristics are analyzed. First, dynamic characteristics of three periodic structures, which are constructed respectively from curved beams, trusses and panels, are investigated by FEA and verified by field tests. Simulation and test results show that curved beams and trusses have good band gaps in high frequency range. Based on this result, new rafts of trusses and curved beams are established subsequently, and their vibration transmission characteristics are analyzed. Lastly, the optimization of dynamic characteristics of the truss raft is studied preliminary. The simulation results show that curved beams and trusses can be used in real rafts. Moreover, the parameters, such as the node masses, can be adjusted to optimize the dynamic characteristics.In Chapter 4, the FRF-based Substructure method is utilized to establish and the model of a truss raft. First, this thesis utilizes the FRF-based Substructure method to analyze the vibration transmission characteristics of a traditional raft system by FEA. Next, the dynamic characteristics of a truss raft system is analyzed by FRF-based Substructure and compared with that of the traditional raft system. The simulation results show that the truss raft system has better vibration isolation characteristics than the traditional one.In Chapter 5, the vibration transmission characteristics of the truss raft system are verified by experiment. An experimental model is built up and experimental results show that the truss raft system has better characteristics of vibration isolation than the traditional raft system.In Chapter 6, conclusions of this thesis are summarized and further work is suggested.