Research On The Vibration And Acoustic Radiation Of Closed Cylindrical Shells With Free Boundary

Cylindrical shells are widely used in various engineering structures. The vibration and acoustic radiation of them receive much research attention. Most of the research work on the vibration and acoustic radiation of submerged finite cylindrical shells is concentrated on the ones with clamped or simple boundary, while little is about the ones with free boundary. Harari proposed a calculation method based on Fourier expansion and the transfer matrix method, which can be used to calculate the vibration and acoustic radiation of cylindrical shells under arbitrary boundary conditions.In this dissertation, a mathematical procedure to calculate the vibration and acoustic radiation of submerged cylindrical shells with free boundary is proposed based on the transfer matrix method utilizing improved Fourier expansion.The main contents and achievements are as follows:1. Based on Flügge Equations, the mechanical model of cylinder shell closed on both ends is established, and a method to transform the solution of complex shape function of cylinder shell into real format is proposed, which can make the search of nature frequency convenient. The nature frequencies of cylindrical shells are analyzed with the proposed method.2. The usual even continuation Fourier expansion is improved by extending the expanding region. Thus the convergence at the end points is improved.3. Utilizing the wave propagation method, together with Ritz method, the forced vibration of cylindrical shells closed on both sides with plates with free boundary is investigated under focusing loads.4. Based on the even continuation Fourier expansion with extended region, a calculation method of the forced vibration of cylindrical shells in the vacuum under radial or longitudinal forces is proposed, and it is verified by comparing with the results obtained utilizing FEM.5. A method to calculate the forced vibration and acoustic radiation of closed cylindrical shells is proposed taking the interaction of fluid and structures into account based on the transfer matrix method and the improved Fourier expansion.In summary, a calculation method to analyze the free vibration of cylindrical shells in vacuum is proposed in this dissertation. The usual Fourier expansion is improved. Based on the improved Fourier expansion, the forced vibration of structures in vacuum is calculated as well as the vibration and acoustic radiation considering the interaction of fluid and structures. The calculation method is validated by comparing to the simulating results of Msc software. These studies are valuable for researches on the vibration and acoustic radiation of structures composed of shafts and the submarine hull.