Study On Vibration Characteristics Of Periodic Structure Vibration Absorption System

Periodic structure refers to the structure whose geometry or material changes periodically.The periodic structure interacts with elastic waves,and the propagation of elastic waves in periodic structures will be greatly attenuated in some specific frequency bands,which are called band gaps.The band gap characteristics of periodic structures can be used to suppress the elastic wave propagation in vibration structures,and then to achieve the purpose of vibration reduction.Therefore,periodic structures have broad application prospects in the field of vibration control.Floating raft vibration isolation is one of the most widely used vibration isolation technologies on warships at present.With the continuous improvement of stealth performance requirements of new warships,the requirements for floating raft vibration isolation technology are becoming higher and higher.The traditional floating raft vibration isolation technology needs to be further improved.Offshore platform is a common platform for offshore energy development,but the complex marine environment such as ocean current,earthquake and so on reduces the vibration of offshore platform.Performance also requires higher requirements,so how to effectively control the vibration of offshore platform structure has always been a research hotspot.In this paper,the band gap characteristics of periodic structures will be studied,and the application of periodic structures in floating raft vibration isolation system of marine auxiliary machinery and vibration reduction of offshore platform structures will be explored.The main contents of this paper are as follows:(1)The band gap of one-dimensional periodic structure is analyzed by lumped mass method.The band gap of one-dimensional infinite periodic structure is calculated by lumped mass method,and the band structure diagram is obtained.The influence of structural geometry and material parameters on the band gap characteristics of periodic structure is studied.The transmission characteristics of one-dimensional finite periodic structure are calculated by finite element method.The results show that the finite periodic structure also has a great attenuation effect on the propagation of elastic wave in the band gap band.It lays a foundation for the research of periodic vibration isolator in the following chapter.(2)The band gap characteristics of periodic isolators are studied,and their effects on the vibration isolation performance of floating raft isolation system are analyzed.The effects of shear wave effect and material order on the transmission characteristics of periodic structures are analyzed.Combining with the modal characteristics of periodic structure,the transmission characteristics of periodic structure are optimized through the section of periodic structure to obtain the first band gap of low frequency and wide band.Finally,a floating raft vibration isolation system with periodic isolator is established and its vibration isolation performance is analyzed.The results show that the vibration isolation effect of the floating raft vibration isolation system has been significantly improved in the bandgap of the periodic isolator.(3)The band gap characteristics of two kinds of periodic honeycomb structures are studied.The band gap characteristics of two periodic honeycomb structures with periodic geometrical changes are analyzed.The band gap characteristics of the two periodic honeycomb structures are obtained by combining the finite element method and the Bloch theorem.The influence of the structural parameters of the cell on the band gap is also studied.(4)The influence of periodic raft on the vibration isolation performance of auxiliary floating raft isolation system is studied.Two kinds of periodic raft structures are designed and the floating raft vibration isolation system of periodic raft is established.The results show that compared with the traditional floating raft vibration isolation system,the periodic raft vibration isolation system has better vibration isolation effect in the middle and high frequency band.The difference of vibration level between the two kinds of periodic raft vibration isolation system is reduced by 8.8 dB and 13.0 dB respectively in the frequency band of 500 Hz-2000 Hz compared with the traditional floating raft vibration isolation system.(5)The vibration reduction performance of truss structures of periodic offshore platforms is studied.Firstly,the periodic duct structure is composed of ducts with different wall thicknesses.The longitudinal and flexural vibration characteristics of the periodic duct are analyzed.The results show that the periodic duct has bandgap characteristics.The effects of the length,number and thickness of the periodic duct element on the bandgap characteristics of the periodic duct are studied.Finally,the application of periodic duct in vibration reduction of offshore platform truss structure is explored.The results show that the periodic duct structure has better vibration reduction effect in the corresponding band gap of the periodic duct structure.