Parametric Randomness And Wave Propagation Method Of Acoustic Radiation Of Thin Plates

The response analysis for stochastic parameter structures has attracted close attention by researchers in recent years, particularly for the acoustic vibration analysis. Since the frequency width is usually very wide in the prediction of structural acoustic radiation, structure acoustic radiation is highly sensitive to the manufacturing technology error, especially in the high frequency. The most ideal condition is that the sensitivity can be determined at the design stage; consequently, the whole performance of the production equipment can be assured. Under this background, a basic problem of the structural noise-acoustic radiation problem of the plate, especially the influence of parameter randomness is studied.By adding several random mass points, the study of plate acoustic radiation property with stochastic parameter is developed using Monte-Carlo simulation. Since the natural frequencies of the structure are changed by the added random mass points, the structural local modification method is applied to avoid solving the natural frequencies and the modes of the new structures repeatedly. The structure acoustic radiation pressure is then derived accordingly, which considerably decreases the calculation amount. Besides, more dynamic modes are required with the increasing of analysis frequency when using the traditional mode decomposition method, which makes calculation amount increase dependently. To solve this difficulty, the symplectic space wave propagation method is applied to derive the accurate dynamic response. Only few waveforms are required in the calculation and all kinds of boundary conditions can be dealt with.The major work of this thesis is as follows:(1) The plate acoustic radiation problem is initially solved using the mode decomposition method. The randomness of the stochastic parameter plate is simulated by adding several random mass points to it, and the acoustic radiation of the plate is then analyzed using the Monte-Carlo simulation. The mass matrix and accordingly the natural frequencies and the modes of the structure need to be updated for each Monte-Carlo sample in the calculation. Finally, the acoustic radiation pressure distribution of the stochastic parameter plate is obtained based on its steady-state response.(2) Structural local modification method is applied to solve the stochastic acoustic radiation problem of the plate. Based on this method, the steady-state response of the new system can be obtained conveniently by adding the modification item to the original system response, and then the response of the stochastic parameter structure can be derived. By avoiding solving the natural frequencies and the modes of the new structures, the calculation amount is considerably decreased without losing accuracy compared with the traditional method in the numerical examples.(3) The direct acoustic radiation of the plate is analyzed using symplectic space wave propagation method. The steady-state response of the thin plate subjected to simple harmonic excitation with four edges simply supported is derived at first, by using which the radiated acoustic radiation pressure of the thin plate is further investigated. The effectiveness of the proposed method is justified by comparison with the traditional mode decomposition method.