Investigation On Active Control Of Structurally Vibration Of And Radiated Sound From Elastic Cylindrical Shell

Active noise control has become a research hotspot in the field of modern vibration and noise control. Especially, the investigation on active control of structurally radiated sound from common structures is of great practical value. In this thesis, the studies on active structural acoustic control are carried out by using the model of a simply supported cylindrical shell of finite length.Firstly, the natural frequencies and mode shapes of the cylindrical shell are analyzed based on the Donnell-Mushtari shell theory. The structural response of cylindrical shell subject to the harmonic point force excitation is derived by applying modal superposition method. The expressions for structural surface mean-square vibration velocity and structural kinetic energy are also formulated.The acoustic radiation characteristics of finitely long cylindrical shell with the simply-supported boundary conditions in an infinite rigid baffle under the point force excitation are investigated in the medium of air. By applying the Kirchhoff-Helmholtz integral and the corresponding Green's function and using the sound pressure as shell loading, as well as Fourier transform and stationary phase method, analytical expressions for the far-field radiated sound pressure, the radiated sound power and the radiation efficiency are obtained. On this basis, the mathematical models for active control of vibration and sound radiation are developed.Two distinct control strategies of structure kinetic energy minimization and radiated sound power minimization are respectively used to develop the active structural acoustic control model. The optimal secondary forces for these two control strategies are calculated according to the Linear Quadratic Optimal Control theory. The global and local active control simulation analysis is performed under these two distinct control strategies.Finally, experimental set-up of a cylindrical shell with simply supported boundary condition is built up. The vibration characteristics of experimental model are measured by applying modal analysis approach. The good agreement is found between the experiment and simulation. Then, the creditability about the simply supported boundary condition of the experimental model is validated. Based on this, the related active control experiments are carried out, and the correctness of the simulation conclusion given in this thesis is then verified by the experimental results.