Analysis And Experiment On Vibration Isolation Characteristcs Of A Floating Raft Composed Of Periodic Structures

The floating raft system is a distribution quality, distribution stiffness and damping complex system which include multiple input and output. By using elastic components and middle quality to absorb and attenuate elastic wave, the system can obtain good ability of vibration isolation. The floating raft system connects marine power machinery with hull structures, and their dynamic characteristics are very important to control the vibration and noise of marine ships. Therefore, a new high efficiency floating raft systems must be designed, we can make full use of vibration transfer and attenuation mechanism to reduce the energy which transfer from the equipment to base. Otherwise, they would seriously affect sound stealth characteristics as well as the safety of submarines. As a result, the new raft has important engineering and military significance.On the basis of previous research results, this thesis uses periodic structure band gap and waveform conversion mechanism to design the high efficiency floating raft. The finite element simulation analysis and experimental method are applied to research the dynamic characteristics and optimize structure.In Chapter 1, the research background of periodic structures as well as the design of rafts are introduced and then the main content of this thesis.In Chapter 2, the Spectrum Element Method and vibration characteristics of periodic structures are investigated. For the beam and rod, the Spectrum Element Method (SEM) is deduced, then, the dynamic characteristics and power flow of some simple plane periodic truss structures are analyzed by SEM and verified by FEA results. The aim of this chapter is to confirm the veracity of SEM and good vibration isolation ability of periodic truss structure. The results show that waveform conversion mechanism is available and provide a theory basis for the raft design.In Chapter 3, the periodic truss structure and curved beam floating raft are designed by using the periodic structure band gap and waveform conversion mechanism. In order to compare the vibration isolation performance, we conduct the modal analysis and harmonious response analysis for the periodic truss raft and traditional raft model in ANSYS, and simply study the optimization of the isolation performance. The simulation results show that the truss structure, compared with the traditional floating raft isolation, has better isolation properties in high frequency and obvious band gap. Moreover, the distribution mass, damping and local structure, to some extent can be adjusted to optimize the dynamic isolation characteristics.In Chapter 4, the waveform conversion effect and energy transfer of power flow in curved beam structure are discussed at first, the conclusions theoretically prove that the vibration isolation characteristics of curved beam structure is excellent. Next, the thesis uses FEA simulation to analyze the vibration transmission characteristics, the result implies the vibration size top-down attenuation step by step, the more layers, the greater the attenuation. Last, the vibration transmission characteristics of periodic curved beam raft is analyzed, compared to the traditional raft, the result shows that curved beam raft has better isolation properties in high frequency.In Chapter 5, the vibration transmission characteristics of the periodic raft system are verified by vibration generator experiment and frequency conversion motor experiment. The experimental results show that the periodic raft system has better characteristics of vibration isolation than the traditional raft system, and it reflect in lower and wider frequency.In Chapter 6, conclusions of this thesis are summarized and further work is suggested.