The Rule Of Low Frequency Acoustic Propagation In Ocean With Layered Elastic Seabed

In China, most of the territorial waters lie to the continent wave, the depth of water is shallow and the gradient is very small, the vast blue territory has very important significance for the development of our national economy and the national security strategy. Acoustic wave is the only form of energy which can be used in underwater long-distance transmission, especially the low-frequency acoustic waves, which has a very important significance for the long-range detection.so making approximate acoustic propagation model on the condition of shallow water low frequency environment is very meaningful.In this paper, the physical model is composed of a shallow water layer, a sedimentary layer of low shear wave velocity and a basal sedimentary layer of high shear wave velocity, normal mode method also be used to study the propagation model of low frequency acoustic field. Normal mode method can produce clear physical images; it has an irreplaceable role for the underwater acoustic propagation attenuation rules of layered elastic seabed environment and the analysis of the physical process of energy conversion.The traditional method of calculating the eigenvalue is finding the root of the dispersion equation in the complex plane, which needs the complex transcendental equation and requires a combination of a variety of numerical methods and tactics of finding roots, the whole process is very complicated. In this paper, to calculate the trapped eigenvalue by using the method of Chebyshev differentiation matrix, which doesn't need a specific analytical form of the dispersion equation except the matrix of discrete differential equations and boundary conditions, this method can give a result with high accuracy and can be implemented easily, what's more, it can also be extended to the horizontal changed case and the root is completed, but the method is not applicable for the calculation of non-trapped mode due to the Chebyshev differentiation matrix is only applicable to limited space problem, the differential matrix combinated with other forms will seriously affect the results, if you want to accurately calculate the unrestricted mode also requires a combination of other ways. The numerical calculation of the eigenfunction is a combination of the approximate solution of Green's function and the reflection coefficient of the seabed. The simulated results of rigid semi-infinite space environment tallied with the rapid field calculation results, and the simulations which are based on the models of the sediments of low transverse wave velocity and the basement of high transverse wave velocity, can get the underwater acoustic propagation rules in the homogeneous medium field.