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• The sound propagation problems of classical/generalized line sources are solved. • The proposed algorithm and program are unconditionally stable. • The proposed algorithm is naturally parallel. • The normal mode solver based on the spectral method can accurately simulate seabeds. A high-precision numerical sound field is the basis of underwater target detection, positioning and communication. A line source in a plane is a common type of sound source in computational ocean acoustics. The exciting waveguide in a range-dependent ocean environment is often structurally complicated; however, traditional algorithms often assume that the waveguide has a simple seabed boundary and that the line source is located at a horizontal range of 0 m, although this ideal situation is rarely encountered in the actual ocean. In this paper, a novel algorithm is designed that can solve for the sound field excited by a line source at any position in a range-dependent ocean environment. The proposed algorithm uses the classic stepwise approximation approach to address the range dependence of the environment and uses the Chebyshev–Tau spectral method to solve for the horizontal wavenumbers and modes of approximately range-independent segments. Once the modal information of these flat segments has been obtained, a global matrix is constructed to solve for the coupling coefficients of all segments, and finally, the complete sound field is synthesized. Numerical experiments using a robust numerical program developed based on this algorithm verify the correctness and usability of our novel algorithm and software. Furthermore, a detailed analysis and test of the computational cost of this algorithm show that it is efficient. [ABSTRACT FROM AUTHOR]

The calculation of a three-dimensional underwater acoustic field has always been a key problem in computational ocean acoustics. Traditionally, this solution is usually obtained by directly solving the acoustic Helmholtz equation using a finite difference or finite element algorithm. Solving the three-dimensional Helmholtz equation directly is computationally expensive. For quasi-three-dimensional problems, the Helmholtz equation can be processed by the integral transformation approach, which can greatly reduce the computational cost. In this paper, a numerical algorithm for a quasi-three-dimensional sound field that combines an integral transformation technique, stepwise coupled modes and a spectral method is designed. The quasi-three-dimensional problem is transformed into a two-dimensional problem using an integral transformation strategy. A stepwise approximation is then used to discretize the range dependence of the two-dimensional problem; this approximation is essentially a physical discretization that further reduces the range-dependent two-dimensional problem to a one-dimensional problem. Finally, the Chebyshev–Tau spectral method is employed to accurately solve the one-dimensional problem. We provide the corresponding numerical program SPEC3D for the proposed algorithm and describe several representative numerical examples. In the numerical experiments, the consistency between SPEC3D and the analytical solution/high-precision finite difference program COACH verifies the reliability and capability of the proposed algorithm. A comparison of running times illustrates that the algorithm proposed in this paper is significantly faster than the full three-dimensional algorithm in terms of computational speed. • An efficient algorithm for quasi-three-dimensional acoustic fields is devised. • The governing equation is decomposed and the solution process is very simple and clear. • The Chebyshev–Tau spectral method can accurately simulate three types of boundaries. [ABSTRACT FROM AUTHOR]

In order to investigate the environment and acoustic filed change induced by typhoon in shallow sea, we conducted two experiments just before and after the passage of typhoon Damrey, which is the strongest to affect the area north of the Yangtze River since 1949, in the Yellow sea in 2012. The data show that the temperature of the whole water column increases dramatically except the sea surface layer after the passage of Damrey while the salinity decreases obviously. The thermocline deepens and weakens, which leads to a change of internal wave activity. The transmission losses (TL) of the two experiments show that the environment change induced by typhoon can increase the TL as large as 8 dB at a distance of 9.2 km and depth of 15 m. The scintillation index (SI) of the sound intensity is simulated to estimate the change of the effect of internal wave activity on acoustic field showing that the SI decreases to a half after the typhoon's passage. The normal mode structures of the two experiments are also significantly different due to the thermocline changes. In addition, the signal arrives earlier after the typhoon's passage due to the water temperature increase. [ABSTRACT FROM AUTHOR]