The Study On Acoustic Transmission Characteristics Of Multi Coupling Vibration Systems

In this thesis,we mainly study the properties of acoustic structures with multi coupling resonances.This thesis consists of four chapters,in addition to the first chapter on the introduction and the last chapter on the results,the main content includes two parts:(1)the acoustic properties of multi coupling resonances;(2)researches on interferometric noise elimination.The detained descriptions on two main chapters are given as follows:The second chapter mainly introduces the sound wave propagation in a multi vibration system.Since the complexity of the vibration system increases rapidly with the freedom of the system,which is difficult to obtain a simple algebraic solution by the restriction of the Abel Ruffini theorem.Therefore,we can just investigate specific characteristics of a multi vibration system,for example the filtering characteristics in a coupling acoustic structure.In addition,we can use the electric-force-acoustic analogy to provide a simple but generic analysis about the characteristics.In a coupling acoustic structure with two vibration components,as two resonant frequencies are different,the coupling effect in the vibrations is weak,so two vibration states can be analyzed separately.In our acoustic devices,the resonant frequencies of the Helmholtz resonator are strongly affected when the resonant frequency of the membrane-mass system is close to the resonant frequency of the Helmholtz resonator.In the case,one can adjust the resonant frequency of the membrane-mass system by changing tension of the membrane to affect the resonance frequency of the Helmholtz resonator.Thus,the acoustic device has potential in the acoustic filtering and sound transmission controlling.The third part introduces how to eliminate sound by the interference effects.It is known that the single negative property of an acoustic material can suppress sound transmission,which is also significant for its noise elimination.However,the fabrication of acoustic metamaterials is complex.There are some difficulties in sound control in practical applications.The sound interference elimination has been investigated for many years.The acoustic device based on the sound interference elimination is easy in fabrication.Therefore,it has a great potential in noise reduction.Generally,the bandwidth of the interferometric noise reduction system is not wide,which restricts its application.Here,we study the optimization of the muffler based on the sound interference elimination.For example,the cascade effects of the multi-pipeline are studied.Meanwhile,some optimizing results are given on the structural parameters of the muffler,which can improve the performance in noise reduction by adjusting the ratio of the length of the pipeline.