Research On Modal Analysis Of Vibration And Acoustic Radiation Of Plate Using Power Modes

In the field of Marine engineering, the vibration of the structure and sound radiation is a long and complex subject. Vibration and noise has enormous influence in the ship's stability, safety, comfort, and warship's combat performance. So in the early stages of ship design, it has to be considered that how to effectively control the structure vibration and noise. However, the noise in the ocean has a complex form. For implementation of effective noise active control, it is necessary to grasp the mechanism of the noise characteristics. Rely on the sound power modes analysis theory, we can accurately calculate the radiation noise level, and can master the rules change with the external incentives, which has great significance for the rapid and effective forecast of structure vibration and noise. Based on the numerical method, modal analysis are researched respectively in the air and water using acoustic power modes, the major work completed is as follows:Based on the finite element method of elastic mechanics, combined with Mindlin bending theory, a finite element model is established and analysed. Rectangular plate's natural frequencies and modes in the vacuum are calculated, and compared with the analytic solutionsThe boundary element method used in the computational acoustics is introduced. Combined with finite element method and the boundary element method based on Rayleigh integral, the expression of the rectangular plate's acoustic power and radiation efficiency was deduced. Fluid-solid coupling movement equation is drawn by using finite element coupling boundary element method. Rectangular plate's natural frequencies and modes in the water are calculated.Modal analysis and control of structural acoustic radiation from a vibrating structure is discussed using the acoustic power mode. The relationship between the radiated acoustic power and the exciting force is obtained based on the quadratic form of the acoustic power and the Rayleigh integral. The acoustic power is then expressed directly by the exciting force as the variable. A plate is involved to show the mode shapes of the acoustic power modes, sound power computation using the power modes and the modal truncation of the power modes. The merits of the acoustic power mode are presented by comparison with the structural vibration mode and acoustic radiation mode.The modes of plate in the water are computerized and analyzed using finite element method and Rayleigh integral coupled method. Because of the fluid loading, the modes of the structure in the water are different with those in the air. The sound power expression of vibration modes and acoustic radiation modes and acoustic power modes were obtained based on the quadratic form of the acoustic power. Acoustic power and radiation efficiency of plate in the water are computerized and compared with those in the air. The numerical results in the water show that vibration has modal interaction at low frequency. The radiation efficiency both in the water and air converge at high frequencies. It is convenient and high-precision that the radiation modes in the water are different with in the air only in the velocity and density. Because of the structure impedance, the radiation efficiency of power modes had amplitude at natural frequencies. Due to using force as variable, power modes have advantage at control.