Research On The Manipulation Of Stop Bands And The Properties Of Sound And Vibration Control For Periodic Structures

Due to the demand of enhancing the equipments’ performance,the increased environmental awareness and comfort criteria,vibration and noise problem receives more and more attenuation.In the transport industry such as spacecraft/aircraft,ships,trains and automobiles,the reduction of vibration and noise has become one of the major concerns.Plates and shells have numerous applications in engineering and are main structures of the vehicle cabins.The interior sound environment is significantly affected by the sound and vibration properties of the plates.Therefore,to reduce the interior noise and vibration of vehicles,a preliminary but effective work is the study of how to reduce the vibration propagation,sound radiation and sound transmission of the plates.In the past several years,the propagation of elastic/acoustic waves in artificial periodic structures has received much attenuation for their unique physical properties and lots of potential applications.One of the most attractive characteristics of periodic structures is the elastic wave stop bands,within which the elastic/acoustic waves cannot propagate freely.This concept provides some new approaches for the reduction of vibration and sound in engineering.This thesis is based on the background of the reduction of interior noise for the vehicles,and its main concern is the vibration and noise control for the plates.Two main contents are involved,that is,stop bands of the periodic plate structures and reduction of vibration and sound based on the periodic structure theory.Firstly,the stop bands of periodic homogeneous plates and periodic sandwich plates are analysed.The means to manipulate and broaden the stop band are studied.Secondly,the vibration and sound properties of the sandwich plates both with and without periodically attached resonators are investigated.The reduction of the vibration and sound are investigated via the periodic structural design.The mechanics of these effects are researched systemically.In addition,to reduce the vibration response and the sound radiation of the plate,the reduction of the force excitation applied on the plate is studied.The periodic isolation structures are used to achieve this goal.The main work and conclusions are as follows:1.The properties,manipulation and broadening of the stop band for the periodic homogeneous plate(PHP)are investigated.The equivalent model of the PHPs with discrete attached structures is developed.Several key and common factors for the effect of the attached structures on the host plate are summarized.A uniform method is proposed,which can be used to analyse the stop bands for the PHPs with different attached structures.Furthermore,based on the equivalent model,the manipulation effects of the stop bands by the equivalent parameters of the attached structures are studied.Several new phenomenon and effects to obtain a wider stop band are discovered.The experimental research about the manipulation and broadening of the stop bands is carried out.Some phenomenon and effects obtained from the theoretical studies are validated.These work can provide some support for the analysis,design and optimization of the stop bands of the PHPs.2.The properties,manipulation and formation mechanisms of the stop band for the periodic sandwich plate(PSP)are studied.Two types of PSPs are designed.The first type of PSP is composed of the host plate and the attached locally resonant units,and the second is composed of the host plate and the attached hard units.The properties and manipulation of the stop bands are analysed.In addition,the simplified physical models for the modes corresponding to the stop band edges are developed.Several essential factors affecting the manipulation law of stop bands are abstracted.These work can offer some reference for the analysis and design of stop bands.Besides,the results obtained from this work can also provide some guidance for analysing and predicting the effects of the structural parameters of PSPs on its stop bands.3.The reduction of vibration and noise for the sandwich plates are studied using the method of periodic structural design.The periodic sandwich plate with attached locally resonant units is considered.The effects of the periodic design on the vibration,sound radiation and sound transmission of this plate are analysed systematically.Especially,the mechanism of the suppression of the vibration and sound is investigated in depth.Furthermore,the experimental research about the reduction of vibration and sound for the sandwich plate is carried out.The effect of periodic design on the vibration and sound of the sandwich plate are validated.In addition,a simplified cabin model is built,which is constructed as an elastic cavity.The feasibility of the applications of periodic structural design in vibration and noise control of the cabin is explored.These work can provide some theoretical foundation for understanding the vibration and sound properties of periodic structures,and advance the use of periodic structure theory in the field of vibration and noise control.4.The control of vibration and sound radiation of the foundation plates is studied via the reduction of the force excitation applied on the plate.The periodic isolation structures are used to suppress the force from the machine to the plate.The effects of the periodic isolator on the vibration and sound of the plate are analysed.Furthermore,by inducing the dynamic absorber and broadening the stop bands of the periodic isolation structures,the isolation performance of the system are improved.Finally,the control of vibration and interior noise of a cabin is studied by using periodic isolators.These work can offer some useful approaches for improving the isolation performance and suppressing the vibration and sound radiation of the foundation plate.In conclusion,this thesis dedicates to the research on the stop bands and the reduction of vibration and sound of periodic plates.The results of this thesis provide some new theoretical guidance and technical supports for the manipulation of wave propagation and the reduction of vibration,sound radiation and sound transmission of the plates.These results can also be a useful reference for the research on stop bands and vibration and noise control of some other engineering structures.