The Research On Vibro-acoustic Characteristics Of Fliud-loaded Damaged Elastic Plate

The ship structure is in multi-excitation condition, it is very significant to research the vibration and acoustic radiation characteristics to improve the warship's vitality and combat capacity. The damage is inescapable for structures during the process of bearing the weigh of all kinds of loads. Comparing with health structures, the damaged structures have different vibro-acoustic characteristics. Based on dynamical changes, damages of structures can be identified and be evaluated. In this paper, a numerical analysis of vibro-acoustic characteristics of fliud-loaded damaged elastic plate is done, the following work is completed:Based on the Mindlin theory, the four-node finite element shell modal of healthy and damaged structure is formed. As for isotropic damage element, the isotropic global weakening of stiffness is used; as for anisotropic damage element, the reduction coefficient of elasticity damage in x and y directions based on Kachanov's theory is used to form stiffening matrix. Applying modal analysis theory, the transfer functions of a elastic plate model with respect to different damage are calculated, and the influence of various types of damage on structure driving by random excitation is studied by using Pseudo-Excitation method.The fluid-structure interaction eqution is established for bodies in the infinite fluid domain, based on theory of Green function and coupled FEM/BEM method. The effect of fliud-loaded is conversed to added mass. Then the interaction eqution is solved by LANCZOS method and the normal velocity is extracted. The acoustic radiation power and acoustic radiation damping of the plate model is calculated; the vibro-acoustic charictristics of the plate and stiffened plate are compared; the influence of different forms of reinforcement on acoustic radiation damping is studied.According to the formation mechanism of acoustic radiation, the acoustic energy is decomposed into the acoustic radiation modes and the mode acoustic radiation damping is induced. The acoustic radiation mode and mode radiation efficiency in light and heavy fluid is compared. In the acoustic radiation modes condition, the acoustic charictaristics of health and damaged structures in light and heavy fluid are studied, and the impact of different excitation and damage condition on acoustic charictaristics is dicussed.