Generation and propagation of anthropogenic underwater noise
Ocean Sciences, Modeling
Research area
Underwater noise pollution is a growing environmental concern, as it significantly impacts marine ecosystems by disrupting the behavior and physiology of aquatic species.
Since different species are sensitive to different frequency ranges, it is crucial to identify major noise sources and characterize their acoustic emissions.
Numerical modeling of sound propagation in the marine environment enables the assessment of anthropogenic noise impact and the development of mitigation strategies.
Project goals
The project focuses on the development of local-scale sound maps for target areas. The idea is that in coastal and shallow-water environments acoustic predictions are strongly affected by the description of the environment, including bathymetry, coastline, seabed structure, bedrock geometry, and seabed elastic modelling.
Within this framework, the work develops along two complementary research lines. One concerns propagation modelling, aimed at performing underwater noise simulation with accurate description of the environment. The second concerns source modelling, with the goal of considering more realistic anthropogenic sources, including directionality, rotation, broadband content, and motion.
The project also perform sensitivity analysis to provide quantitative indications of the possible over- or under-estimation of sound pressure levels, and to better understand under which conditions simplified approaches remain reliable and when more detailed site-specific modelling is needed.
Computational approach
Simulating wave propagation in real marine environments poses several numerical challenges. One of the main difficulties is achieving high accuracy while minimizing computational costs, especially when dealing with complex geometries that are reproduced through undtructured and coupled fluid-solid interactions. Specfem3D, which utilizes the spectral element method (SEM), is a promising tool due to its ability to provide highly accurate solutions with reduced computational demands. Moreover, we are comparing Specfem3D with two solvers based on finite difference (FD) and finite volume (FV) methods. FD methods are known for their simplicity and efficiency in structured grids but. FV methods, on the other hand, offer flexibility in handling unstructured meshes. By systematically benchmarking these solvers, we aim to establish the optimal applicability range. Overcoming these computational challenges will enable more accurate environmental impact assessments and contribute to the development of effective noise pollution mitigation strategies.
Image
(a) SPL on the x-y plane passing through a 25Hz monopole source placed 40m below the free surface in a Gaussian Canyon bathymetry, computed with Specfem3d; (b) Gaussian Canyon geometry; (c) SPL on the y-lines x = 0, z = 30m computed with Specfem3D compared with Helmhotz solution.
Key results
The project achieved significant methodological and applied results in advanced source modeling and wave propagation in complex environments.
On the source side, systematic simulations were carried out within the Gaussian canyon benchmark geometry, comparing monopoles with rotating multipole sources (rotpoles) at different rotation frequencies. These tests demonstrated that source representation strongly affects the acoustic pressure, in near and far field, showing that realistic ship-noise assessment requires an advanced source characterization.
On the propagation side, full 3D time-domain simulations were carried out using a software that handle unstructured meshes and fluid-solid coupling, enabling a high-fidelity representation of marine environments. Within this framework, two case studies were considered in the Gulf of Trieste: a coastal area, where ship-noise propagation was investigated, and a small offshore area, where a Mini-GI experimental survey provided data for comparison with numerical results.
In the latter, we focused on the role of environmental description. Sensitivity analyses were performed on both geometrical and geophysical parameters, allowing us to quantify how seabed structure affects acoustic levels in the water layer. We evaluate also the impact of representing the seabed as an equivalent fluid versus an elastic solid, and the differences between 2D and 3D acoustic mapping approaches.
Resource usage
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What's next
I intend to continue developing this workflow for site-specific sound maps in coastal and shallow-water environments. Future work will focus on new areas of interest involved in European projects, including the Norwegian coasts and on other anthropogenic noise sources, such as off-shore wind farms. We plan to increase the spatial extent of the domains, while still considering an accurate description of the environment. The numerical framework will rely on the SPECFEM3D solver, based on Spectral Element Method, which is particularly suited to complex marine environments representation. We will exploit GPU architectures in order to make larger simulations feasible. In this perspective, the Leonardo HPC infrastructure at CINECA will be a key resource for scaling up the methodology and apply it to more computationally demanding scenarios.
Image
Workflow of the project: source characterization and propagation modelling. Source characterization starts from CFD simulations and, through acoustic analogy, leads to the construction of synthetic analytical moving sources. Propagation modelling is then performed in site-specific areas (showed: costal area of the Trieste Gulf) with an accurate environmental description to produce local-scale TL sound maps.
Ines Addeo
University of Trieste; Istituto Nazionale di Oceanografia e di Geofisica Sperimentale
I am Ines Addeo, a 25-year-old mathematician with a strong background in both pure and applied mathematics. I earned my Bachelor's degree in Mathematics in 2020 from the University of Naples Federico II and completed my Master's in Computational Mathematics and Modelling at the University of Trieste in 2023. During my final year, I developed a strong interest in applied mathematics after years of focusing on theoretical aspects. My Master's thesis explored the fluid dynamics phenomenon of cavitation. In November 2023, I started a PhD in the *Earth science, fluid-dynamics and mathematics. Interactions and methods* program, where I focus on underwater acoustics and numerical modeling of acoustic wave propagation in real marine environments.