Study On Acoustic Vibration Propagation Characteristics And Vibration And Noise Reduction Design Of Fluid-structure Interaction Periodic Pipe

The pipe systems are used to transfer unimpeded flow of air,water and oil in equipment.They are paramount to maintain the normal operation.The pulsation of fluid pressure and vibration of pipe wall in such pipe systems lead to the complicated fluidstructure interaction.Both the pulsation and vibration of them can generate radiation noise.Meanwhile,the vibration couples with the radiation noise and they are mutually influenced,which makes the problem of the vibration and noise be more prominent.The coupled noise and vibration in pipe systems,especially the low-frequency components,greatly reduce the safety and quietness of the equipment.Therefore,the reduction of vibration and noise in pipe system has become one of the major concerns.Traditional technologies can hardly reduce the low-frequency and broadband vibration and noise in pipe systems.There are urgent requirements for new theories,technologies and methods.The Phononic Crystals and Acoustic Metamaterial,the frontier fields in condensed matter physics,can provide bandgap for efficiently suppressing the propagation of elastic/acoustic waves in the fluid-structure interaction pipe system.The essence of acoustic vibration suppression is wave manipulation,which means,Phononic Crystal and Acoustic Metamaterial theories can offer new technical support and theoretical basis for the vibration and noise control of the fluid-structure interaction pipe system.This thesis systematically studied the properties and reduction approaches of sound and vibration propagation in liquid-filled pipe structures based on the Phononic Crystals and Acoustic Metamaterial theories.To achieve great vibration and noise reduction of the pipe systems,the bandgaps of both elastic and acoustic waves are realized through the periodic design,respectively.The main work and results are as follows:1.This thesis improves the theoretical model and analysis method for sound and vibration propagation in the fluid-structure interaction periodic pipe system.For periodic fluid-filled pipe system,it establishes the transfer matrix method for calculating the vibration band gap under complex external load.It deduces the acoustic transfer matrix of the equal cross section pipe,variable cross section pipe and Helmholtz resonator.Then,the acoustic transfer matrix of the entire complex pipe muffler is established.It establishes an acoustic-electric analogy method for analyzing the acoustic characteristics of gas-liquid cavity pipe muffler.Moreover,a dynamic model for the analysis of flow induced vibration characteristics of the periodic pipe system is established.For flexible pipes,this manuscript proposes a transfer matrix method based on the equivalent sound velocity(i.e.,Korteweg wave velocity),and finds the low-frequency band gap of periodic flexible pipe for sound insulation.The thesis validates the accuracy of these models and methods.2.This thesis analyzes the vibration transmission characteristics in fluid-structure interaction periodic pipe system under complex loading conditions.For the fluid-structure coupled vibration in periodic pipe,the manuscript investigates the influences of complex loading conditions(includes fluid velocity,axial load,pressure and fluid temperature)on the vibration band gaps of the two periodic pipes,and their mechanisms are revealed.Based on the finite element platform,ANSYS,the thesis analyzes the fluid-induced vibration of the two kinds of periodic pipelines in different fluid states by adopting the one-way and two-way fluid-structure interaction algorithms.3.This thesis studies the characterstics of sound propagation and noise reduction design in fluid-structure interaction periodic pipe system.A pipe muffler with ultra-low frequency and ultra-wide band is proposed.By introducing an air bag into the resonance chamber of the Helmholtz muffler,a new design of a Helmholtz muffler is proposed.This muffler features ultra-low frequency and ultra-wide band gap of sound insulation within 11-496 Hz.Based on this concept,an ultra-low frequency and broad-band pipe muffler with expanding gas-liquid cavity is conceived,and it can generate a bandgap of51-1071 Hz.The influences of key parameters on the bandgaps are discussed in detail and the sound attenuation mechanism is revealed thoroughly.Moreover,an improved transfer matrix method is proposed by considering the fluid velocity.This model can accurately predict the influences of fluid velocity on different pipe mufflers.In addition,a periodic flexible pipe with variable section is designed,which can suppress the low-frequency noise.Its sound propagation characteristics are analyzed and the sound attenuation mechanism is revealed.4.This work accomplishes the experimental validation of the sound and vibration propagation characteristics in the fluid-structure interaction periodic pipe system.The experimental platform is built to measure vibration transmission in the Bragg periodic pipe and the Local Resonance periodic pipe under different fluid conditions.Moreover,this work tests the sound propagation in the Helmholtz muffler,the gas-liquid cavity Helmholtz pipe muffler and the periodic flexible pipe with variable section.The experimental results can effectively verify the accuracy of theoretical design and calculation results.In summary,this thesis systematically investigates the properties of sound and vibration propagation in the fluid-structure interaction pipe system.The new calculation method and design concept for controlling pipe vibration and noise are proposed and completed.This thesis thoroughly studies the vibration band gaps and its attenuation mechanisms under complex loading states.Moreover,an ultra-low frequency and ultra-wide band mufflers is firstly proposed for efficient noise reduction.Experiments are carried out and verify theoretical results.The research results are expected to provides new theories,technologies and methods for the vibration and noise control in fluid-structure interaction pipe system.