arXiv subjects

Juan D. Gonzalez

Publications and source records attributed to Juan D. Gonzalez.

6 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↗

arXiv2021

Robust Model-Based Clustering

We propose a new class of robust and Fisher-consistent estimators for mixture models. These estimators can be used to construct robust model-based clustering procedures. We study in detail the case of multivariate normal mixtures and propose a procedure that uses S estimators of multivariate location and scatter. We develop an algorithm to compute the estimators and to build the clusters which is quite similar to the EM algorithm. An extensive Monte Carlo simulation study shows that our proposal compares favorably with other robust and non robust model-based clustering procedures. We apply ours and alternative procedures to a real data set and again find that the best results are obtained using our proposal.

stat.ME↗

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↗

arXiv2019

Robust Clustering Using Tau-Scales

K means is a popular non-parametric clustering procedure introduced by Steinhaus (1956) and further developed by MacQueen (1967). It is known, however, that K means does not perform well in the presence of outliers. Cuesta-Albertos et al (1997) introduced a robust alternative, trimmed K means, which can be tuned to be robust or efficient, but cannot achieve these two properties simultaneously in an adaptive way. To overcome this limitation we propose a new robust clustering procedure called K Tau Centers, which is based on the concept of Tau scale introduced by Yohai and Zamar (1988). We show that K Tau Centers performs well in extensive simulation studies and real data examples. We also show that the centers found by the proposed method are consistent estimators of the "true" centers defined as the minimizers of the the objective function at the population level.

stat.CO↗

arXiv2018

Modelling High-Frequency Backscattering from a Mesh of Curved Surfaces Using Kirchhoff Approximation

The Kirchhoff approximation (K-A) to calculate the acoustic backscattering of a complex structure can be evaluated using a discretized version of its surface (i.e. a $\textit{mesh}$). From the computational viewpoint, the most accesible approach is the one based on flat facets. However, in the high frequency range, where the K-A provides good agreement and is therefore applicable, it requires a mesh with such a large number of facets that it turns impractical. To avoid these difficulties a mesh of curved triangles can be used to model the scatterer's complex structure. Previous computational implementations reported in the literature did not accomplish satisfactory results for high frequency. In this work we propose a numerical model based upon an iterative integration using Gauss-Legendre rules. The model was validated against exact solutions and led us to achieve adequate results in the high-frequency range.

physics.comp-ph↗