| To solve the problem of predicting the acoustic radiation field of the double-layer elastic shell structure submerged in water, in this dissertation, the algorithm and the program of the BEM have been developed independently. Three methods which are the polar coordinate transformation, the transformation of the degenerative element for linear quadrilateral element, and the generalized polar coordinate transformation are adopted for dealing with the singular integrals in the algorithm of the BEM; The non-uniqueness problem of the BEM at characteristic frequencies has been solved effectively in two ways. One is the CHIEF method, the other one is the combination of the interior helmholtz equation and its derivatives to form a new extra equation. To verify the accuracy and feasibility of those methods, the sound field for three kinds of sound sources, including a pulsating sphere, the combination of the point sources and an elastic structure with the known normal velocity on its surface, has been calculated by use of the self-developed algorithm, the analytical method, and by use of Sysnoise software respectively, and very good agreement has obtained.In addition, the fluid-solid coupling FEM algorithm has been improved and complemented in this dissertation on considering the rayleigh damping multiplier Alpha and Beta. The accuracy of the FEM algorithm improved is tested.The algorithm combination of the FEM and the BEM has been constructed to solve the structural-acoustic coupled problem of the elastic structure submerged in water. The validity of the combinated algorithm is tested by means of the comparison between the results calculated by use of the algorithm improved and that by use of Sysnoise.At last, the validity of the self-developed BEM algorithm for predicting the acoustic radiation field of elastic structures submerged in water is tested by an experiment in Qiandao Lake, in which the experimental model is a double-layer cylindrical elastic shell. |
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