Abstract
A three-dimensional (3D) finite difference (FD) model with formal fourth-order accuracy has been developed for the ocean acoustic Helmholtz equation (HE), which can be used to address arbitrary bathymetry and provide more accurate benchmark solutions for other 3D underwater acoustic approximate models. The derivatives in the acoustic HE are numerically discretized based on regular grids, and the perfectly matched layer is introduced to absorb unphysical reflections from the boundaries where Sommerfeld radiation conditions are deployed. The system of linear equations is solved using a parallel matrix-free geometric multigrid preconditioned biconjugate gradient stabilized iteration method, and the code (named COACH) is run on the Tianhe-2 supercomputer in China. Four 3D topographic benchmark acoustic cases-a wedge waveguide, Gaussian canyon, conical seamount, and corrugated seabed-are simulated to test the present FD model, and the maximum number of grid points reaches 33.15 × 109 in the wedge waveguide case, running in parallel with 988 central processing unit cores. Furthermore, the accuracy and generality of the present model have been verified by solution comparisons with other available 3D acoustic propagation models, and the two-dimensional and 3D transmission loss contours are presented to facilitate the distinguishing among the acoustic field features of these cases.
Highlights
Acoustic waves can propagate long distances in water because they experience less energy attenuation than electromagnetic waves and, have been widely used in acoustic systems for underwater target detection and localization, estimation of marine environmental properties, and underwater communication
If the acoustic field is time harmonic, which means that the physical pressure has the form of p 1⁄4 PeÀixt (P is the complex pressure in the frequency domain, and eÀixt is the time factor), the wave equation in the time domain can be changed to the elliptic Helmholtz equation (HE) in the frequency domain, which can be discretized using direct numerical methods such as the finite difference method (FDM) and FEM
As a direct numerical approach, the present FDM model is of great value for simulating the acoustic propagation for arbitrary seafloor topographies accurately, providing benchmark solutions for other approximate underwater acoustic propagation models, such as the PE, and analyzing the acoustic field with complex structures using 3D visualization methods, especially inside the near-source region in several wavelength ranges resulting from the full-field simulation capability of this FDM model
Summary
Acoustic waves can propagate long distances in water because they experience less energy attenuation than electromagnetic waves and, have been widely used in acoustic systems for underwater target detection and localization, estimation of marine environmental properties, and underwater communication. Underwater three-dimensional (3D) acoustic propagation effects can arise from many oceanographic (eddies and fronts) and topographic features (wedges, ridges, and seamounts; Tolstoy, 1996), and the reflection, refraction, and scattering of acoustic energy in the horizontal directions can result in substantial problems with underwater acoustic signal processing systems; modeling 3D sound propagation is very valuable and is receiving a great deal of attention in the field of computational ocean acoustics such that it has become a research hotspot in recent years. The image source methods can accurately simulate the 3D acoustic field in the waveguides with the planar seabed (Tang et al, 2018), the coupled-mode methods commonly predict the 3D sound propagation in the axisymmetric or horizontal symmetric marine environments (Luo and Zhang, 2015), the ray model or beam tracing methods can be applied to the 3D high-frequency sound propagation simulations (Porter, 2019), the powerful 3D parabolic equation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
