arXiv subjects

Edmundo F. Lavia

Publications and source records attributed to Edmundo F. Lavia.

4 recordsLinked to original sources

arXiv2023

TetraScatt model: Born approximation for the estimation of acoustic dispersion of fluid-like objects of arbitrary geometries

Modelling the acoustic scattering response due to penetrable objects of arbitrary shapes, such as those of many marine organisms, can be computationally intensive, often requiring high-performance computing equipment when considering a completely general situation. However, when the physical properties (sound speed and density) of the scatterer object under consideration are similar to those of the surrounding medium, the Born approximation provides a computationally efficient way to calculate the scattering. For simple geometrical shapes like spheres and spheroids, the acoustic scattering in the far field can be evaluated through the Born approximation recipe as a formula which has been historically employed to predict the response of weakly scattering organisms, such as zooplankton. Moreover, the Born approximation has been extended to bodies whose geometry can be described as a collection of non-circular rings centred on a smooth curve. In this work, we have developed a numerical approach to calculate the far-field backscattering by arbitrary 3D objects under the Born approximation. The object's geometry is represented by a volumetric mesh composed of tetrahedrons, and the computation is efficiently performed through analytical 3D integration, yielding a solution expressed in terms of elementary functions for each tetrahedron. The method's correctness has been successfully validated against benchmark solutions. Additionally, we present acoustic scattering results for species with complex shapes. To enable other researchers to use and validate the method a computational package named tetrascatt implemented in the R programming language was developed and published in the CRAN (Comprehensive R Archive Network).

physics.comp-ph↗

arXiv2022

A 3D acoustic propagation model for shallow waters based on an indirect Boundary Element Method

The purpose of this work is twofold: (a) To present the theoretical formulation of a 3D acoustic propagation model based on a Boundary Element Method (BEM), which uses a half-space Green function in place of the more conventional free-space Green function and (b) to show a numerical implementation aimed to explore the formulation in simple idealized cases --controlled by a few parameters--, and provides necessary tests for the accuracy and performance of the model. The half-space Green's function, which has been used previously in scattering and diffraction, adds terms to the usual expressions of the integral operators without altering their continuity properties. Verifications against the Pekeris waveguide suggest that the model allows an adequately prediction for the acoustic field. Likewise, numerical explorations in relation to the necessary mesh size for the description of the water-sediment interface allow us to conclude that a TL prediction with acceptable accuracy can be obtained with the use of a bounded mesh around the desired evaluation region.

physics.comp-ph↗

arXiv2019

Boundary-element method to analyze acoustic scattering from a coupled swimbladder-fish body configuration

A model for computing acoustic scattering by a swimbladdered fish with coupling to surrounding fish tissue that is assumed to behave as a homogeneous fluid, is presented. Mathematically, this corresponds to considering the problem of two penetrable scatterers immersed in a homogeneous medium, one of which is wholly embedded in the other. The model is formulated in the frame of boundary integral equations whose solution is achieved using the Boundary Element Method (BEM) for a planar triangle mesh. The numerical implementation is verified against benchmark solutions reported in the literature. The model is then applied to a specimen of \textit{Merluccius hubbsi}, whose morphometry was determined by CT scanning, for evaluating its forward and backscattering responses. From the acoustic scattering viewpoint, the swimbladder is considered as a gas-filled object while the flesh constituting the fish body acts like a weak scatterer. The numerical results suggest the swimbladder and the fish body responses, when fully coupled, can lead to substantial differences with respect to the simplified models normally in use in the area of aquatic ecosystem research.

physics.comp-ph↗

arXiv2018

A Computational Method to Calculate the Exact Solution for Acoustic Scattering by Fluid Spheroids

The problem of scattering of harmonic plane acoustic waves by fluid spheroids (prolate and oblate) is addressed from an analytical approach. Mathematically, it consists in solving the Helmholtz equation in an unbounded domain with Sommerfeld radiation condition at infinity. The domain where propagation takes place is characterised by density and sound speed values $ρ_0$ and $c_0$, respectively, while $ρ_1$ and $c_1$ are the corresponding density and sound speed values of an immersed object that is responsible of the scattered field. Since Helmholtz equation is separable in prolate/oblate spheroidal coordinates, its exact solution for the scattered field can be expressed as an expansion on prolate/oblate spheroidal functions multiplied by coefficients whose values depend upon the boundary conditions verified at the medium-immersed fluid obstacle interface. The general case ($c_0 \neq c_1$) is cumbersome because it requires to solve successive matrix systems that are ill-conditioned when $c_1/c_0$ is far from unity. In this paper, a numerical implementation of the general exact solution that is valid for any range of eccentricity values and for $c_0 \neq c_1$, is provided. The high level solver code has been written in the Julia programming language while a software package recently released in the literature has been used to compute the spheroidal functions. Several limit cases (Dirichlet and Neumann boundary conditions, spheroid tending to sphere) have been satisfactorily verified using the implemented code. The corresponding example scripts can be downloaded from the authors' web (GitHub) site. Additionally, the new code has been used to extend results reported in the literature.

physics.comp-ph↗