The Vibration And Sound Radiation Of Circular Cylindrical Shells

The rapid development of modern urban rail transit has inevitably induced pollutions, such as environmental vibration and noise, to the residents living along the rail lines. And as a result of people's concern about their living environment, more and more attention has been paid to these problems. To the viaduct, the widely used cross-section of the bridge has the form of box, which is similar to the musical instrument - drum in some extent, so the low-frequency noise radiated from the viaduct is usually remarkable when the train traverses on it.The problem of acoustic radiation of the vibrating box beam is essentially the one of fluid-structure vibroacoustic coupling, which is always a frontier in structural acoustics and noise control, and also a recognized intricate problem. The box structure with two open ends in engineering is made of four plates, whose thickness is usually small compared with the length and width, thus it can be treated as a thin shell theoretically. In general, the thin shell with box cross-section is much more complex and difficult than the circular cylindrical shell to be analyzed. But in essence, the vibration induced acoustic radiation of both fall into the problem of fluid-structure coupling. Therefore, on one hand to simplify the research, and on the other to lay a good foundation of the investigation of structure-borne noise of the box beam in viaducts, circular cylindrical shell is regarded as the research object, and the contentsare listed as follows:1. The basic vibration equations of thin shells and motion equations of circular cylindrical shells in the theory of Reissner are introduced in brief. And it is pointed out that the difference between the diverse theories of thin shells' vibration is with a minor magnitude.2. The software of the Finite Element Analysis (FEA) is employed to analyze the modes of a circular cylindrical shell with two close ends, and frequencies and relevant mode shapes are obtained. There are several types of modes, including axial mode, shell bending mode, beam bending mode, shell torsion mode.3. Based on the shell vibration theory of Kennard and by means of the Wavenumber Domain Approach (WDA), the velocity of the infinite circular cylindrical shell, which is internally filled with air and externally submerged in air and excited by a single fixed harmonic load, is acquired. Then the far field acousticpressure is formulated by the Stationary Phase Method (SPM).4. By mathematic programming, the curves of far field Sound Pressure Level (SPL) to frequency at different observation points and SPL related to different damping ratios of the shell are obtained. Also, the influences of some parameters to the far field SPL, including damping ratio, amplitude of the excitation, elastic modulus, radius of the shell, with or without the internal air, etc., are investigated.In the end, the contents of this thesis have been summarized and some problems which need further study have been proposed.