Jun Tang

Effect of acoustic horizontal refraction on DOA estimation with a single vector hydrophone

The effect of horizontal refraction (HR) on DOA estimation with a single vector hydrophone is studied. It has been demonstrated in a previous study that HR may bring about a significant deviation between the true bearing of the source and the direction of time-averaged sound flux at the receiver point, i.e., DOA estimation error. [J. Tang et al., 2018, 43(2), ACTA ACUSTICA (in Chinese)]. In the present work, the DOA estimation error in a more realistic scenario is studied, more precisely, source signals are considered to be wide-band instead of time-harmonic, and meanwhile ambient noise is added to the received signal. The ocean waveguide used in simulations is a 3D version of the standard ASA wedge, which implies that the HR considered in this work is raised from multiple reflections between a horizontal sea surface and a sloping sea bottom. The results of this work shall offer some reference to DOA estimation in circumstances with strong HR effects.

On the Method of Source Images for the Wedge Problem Solution in Ocean Acoustics: Some Corrections and Appendices

In this study the method of source images for the problem of sound propagation in a penetrable wedge [G. Deane and M. Buckingham, J. Acoust. Soc. Am. 93 (1993) 1319–1328] is revisited. This solution is very important three-dimensional (3D) benchmark in computational underwater acoustics, since a wedge bounded from above by the sea surface and overlying a sloping penetrable bottom is the simplest model of a shallow-sea waveguide near the coastline. The corrected formulae for the positions of the source images and bottom images are presented together with the explanation of their derivation. The problem of branch choice in the reflection coefficient is thoroughly discussed, and the corresponding explicit formulae are given. In addition, numerical validation of the proposed branch choice schemes and the resulting wedge problem solutions are presented. Finally, source images solution is computed for a series of examples with different ratios of shear and bulk moduli in the bottom. The interplay between the acoustic-elastic waves coupling and the horizontal refraction in the wedge is demonstrated.

On the source images method for sound propagation in a penetrable wedge: Some corrections and appendices

Some corrections and supplements for the source images method in the case of the penetrable wedge, proposed by Deane & Buckingham (1993), are introduced. The problem of sound propagation in a wedge-like waveguide is an important three-dimensional benchmark in underwater acoustics. Firstly, the formulae for positions of source images and bottom images are corrected. Secondly, a simple branch selection rule for the square root in the reflection coefficient is formulated and validated by several numerical tests. New examples, where the source images method is used to simulate time-harmonic acoustic fields and the pulse signal propagation, are presented.

An analysis of horizontal refraction in the problem of sound propagation in wedge-shaped oceans

This work is aimed at exploring characteristics of horizontal refraction in three-dimensional sound propagation. The horizontal refraction angle is used as the indicator for evaluating strength of horizontal refraction effects. The horizontal refraction angle, as well as the sound fields, in a series of wedge-shaped ocean waveguides with different bottom parameters are simulated. Furthermore, the influence of bottom parameters on strength of horizontal refraction effects is discussed.

Applications of seismo-acoustic propagation modelling: Nuclear explosion and wind turbine noise

The parabolic equation (PE) method and the finite element method (FEM) are both applied to modelling of seismic wave propagation in two issues: nuclear explosion and wind turbine noise. Explosion inside the elastic layer is modelled as delta function and its derivatives in both P and S wave equations in PE, while as the combination of normal and tangential displacements in FEM. Meanwhile, pile driving noise from wind farms is modeled as downwards force source in both FE and FEM. Good agreement between the PE and FEM for the problems with buried compression source, buried shear source, and force source proves the accuracy for both of them.

Perfectly matched layer for an elastic parabolic equation model in ocean acoustics

The perfectly matched layer (PML) is an effective technique for truncating unbounded domains with minimal spurious reflections. A fluid parabolic equation (PE) model applying PML technique was previously used to analyze the sound propagation problem in a range-dependent waveguide (Lu and Zhu, 2007). However, Lu and Zhu only considered a standard fluid PE to demonstrate the capability of the PML and did not take improved one-way models into consideration. They applied a [1/1] Padé approximant to the parabolic equation. The higher-order PEs are more accurate than standard ones when a very large angle propagation is considered. As for range-dependent problems, the techniques to handle the vertical interface between adjacent regions are mainly energy conserving and single-scattering. In this paper, the PML technique is generalized to the higher order elastic PE, as is to the higher order fluid PE. The correction of energy conserving is used in range-dependent waveguides. Simulation is made in both acoustic cases and seismo-acoustic cases. Range-independent and range-dependent waveguides are both adopted to test the accuracy and efficiency of this method. The numerical results illustrate that a PML is much more effective than an artificial absorbing layer (ABL) both in acoustic and seismo-acoustic sound propagation modeling.

Broadband modeling of sound propagation in shallow water with an irregular elastic bottom

The purpose of this work is to study the propagation of broadband sound pulses in shallow water environments. It is essential for an underwater pulse propagation model to handle bottom interaction, range-dependence, and wide-angle propagation in shallow water. Therefore, a comparatively realistic model that consists of a fluid overlying an irregular elastic bottom is treated, where the effects of shear wave are included. The range-dependent seismo-acoustics problem in frequency-domain is solved by a parabolic equation model. Fourier synthesis of frequency-domain solutions is implemented to model the received time series of a broadband sound propagation. And parallel programming is tried to improve the computational efficiency. Dispersion characteristics are exhibited by multiple mode arrivals during the propagation, including the dispersion of normal modes and mode 0 (the Scholte wave). The dispersion analysis of normal modes and the Scholte wave are demonstrated under different types of elastic bottoms. ...

Broadband modeling of sound propagation in shallow water with an elastic bottom

Broadband sound propagation in shallow water is studied in this work. It is essential for a shallow water sound propagation model to involve the effects of bottom interaction and range-dependence. Therefore, a realistic model that consists of a fluid overlying an elastic sloping bottom is treated in this paper, where the effects of shear waves are included. An approach to calculate the vector sound field is presented. The range-dependent seismo-acoustics problem in the frequency-domain is solved by the parabolic approximation method, and the Fourier synthesis technique of the frequency-domain solutions is implemented to model the received time series of a broadband sound propagation. Due to the elastic boundary conditions, the Scholte waves that travel along the ocean bottom are generated. Dispersion characteristics of the normal modes and the Scholte waves are exhibited by multiple mode arrivals during the propagation. The dispersion curves of normal modes and the Scholte waves are demonstrated for the c...