1,720,976 research outputs found
Computation of viscoelastic shear shock waves using finite volume schemes with artificial compressibility
Get PDFThe formation of shear shock waves in the brain has been proposed as one of
the plausible explanations for deep intracranial injuries. In fact, such
singular solutions emerge naturally in soft viscoelastic tissues under dynamic
loading conditions. To improve our understanding of the mechanical processes at
hand, the development of dedicated computational models is needed. The present
study concerns three-dimensional numerical models of incompressible
viscoelastic solids whose motion is analysed by means of shock-capturing finite
volume methods. More specifically, we focus on the use of the artificial
compressibility method, a technique that has been frequently employed in
computational fluid dynamics. The material behaviour is deduced from the
Fung--Simo quasi-linear viscoelasiticity theory (QLV) where the elastic
response is of Yeoh type. We analyse the accuracy of the method and demonstrate
its applicability for the study of nonlinear wave propagation in soft solids.
The numerical results cover accuracy tests, shock formation and wave focusing
Modélisation de la propagation d'ondes dans les solides non linéaires à dynamique lente
No full textGeomaterials such as rocks and concrete are known to soften under a dynamic loading, i.e., the speed of sound diminishes with forcing amplitudes. To reproduce this behavior, an internal-variable model of continuum is proposed. It is composed of a constitutive law for the stress and an evolution equation for the internal variable. Nonlinear viscoelasticity of Zener type is accounted for by using additional internal variables. The equations of motion write as a nonlinear and nonhomogeneous system of conservation laws. This system of partial differential equations is solved numerically using finite-volume methods. An analytical solution to the Riemann problemof nonlinear elastodynamics is provided, which is used to benchmark the performances of the numerical methods. Numerical results are in qualitative agreement with experimental results from resonance experiments (NRUS) and dynamic acousto-elastic testing (DAET). Similar methods are developed in 2D to perform wave propagation simulations. In the framework of harmonic-based continuation methods, a numerical method is developed for the computation of periodic solutions. Based on a finite element discretization of the equations of motion, this frequency-domain method provides fast resonance simulations, which is useful to carry out experimental validations.Les géomatériaux tels les roches et le béton ont la particularité de s’amollir sous chargement dynamique, c.-à-d. que la vitesse du son diminue avec l’amplitude de forçage. Afin de reproduire ce comportement, un modèle de milieu continu à variables internes est proposé. Il est composé d’une loi de comportement donnant l’expression de la contrainte, et d’une équation d’évolution pour la variable interne. La viscoélasticité non linéaire de type Zener est prise en compte par l’ajout de variables internes supplémentaires. Les équations du mouvement forment un système de lois de conservation non linéaire et non homogène. Le système d’équations aux dérivées partielles est résolu numériquement à l’aide de la méthode des volumes finis. Une solution analytique du problème de Riemann de l’élastodynamique non linéaire est explicitée. Elle est utilisée pour évaluer les performances des méthodes numériques. Les résultats numériques sont en accord qualitatif avec les résultats expérimentaux d’expériences de résonance (NRUS) et d’acousto-élasticité dynamique (DAET). Des méthodes similaires sont développées en 2D pour réaliser des simulations de propagation d’ondes. Dans le cadre des méthodes de continuation reposant sur la décomposition en harmoniques, une méthode numérique est développée pour le calcul de solutions périodiques. Sur la base d’une discrétisation éléments finis des équations du mouvement, cette méthode fréquentielle donne des simulations de résonance rapides, ce qui est utile pour mener des validations expérimentales
Nonlinear plane waves in saturated porous media with incompressible constituents
No full textWe consider the propagation of nonlinear plane waves in porous media within the framework of the Biot–Coussy biphasic mixture theory. The tortuosity effect is included in the model, and both constituents are assumed incompressible (Yeoh-type elastic skeleton, and saturating fluid). In this case, the linear dispersive waves governed by Biot’s theory are either of compression or shear-wave type, and nonlinear waves can be classified in a similar way. In the special case of a neo-Hookean skeleton, we derive the explicit expressions for the characteristic wave speeds, leading to the hyperbolicity condition. The sound speeds for a Yeoh skeleton are estimated using a perturbation approach. Then we arrive at the evolution equation for the amplitude of acceleration waves. In general, it is governed by a Bernoulli equation. With the present constitutive assumptions, we find that longitudinal jump amplitudes follow a nonlinear evolution, while transverse jump amplitudes evolve in an almost linearly degenerate fashion.This work was supported by the Irish Research Council (project ID GOIPD/2019/328)
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Computation of viscoelastic shear shock waves using finite volume schemes with artificial compressibility
No full textThe formation of shear shock waves in the brain has been proposed as one of the plausible explanations for deep intracranial injuries. In fact, such singular solutions emerge naturally in soft viscoelastic tissues under dynamic loading conditions. To improve our understanding of the mechanical processes at hand, the development of dedicated computational models is needed. The present study concerns three-dimensional numerical models of incompressible viscoelastic solids whose motion is analysed by means of shock-capturing finite volume methods. More specifically, we focus on the use of the artificial compressibility method, a technique that has been frequently employed in computational fluid dynamics. The material behaviour is deduced from the Fung–Simo quasi-linear viscoelasiticity (QLV) theory where the elastic response is of Yeoh type. We analyse the accuracy of the method and demonstrate its applicability for the study of nonlinear wave propagation in soft solids. The numerical results cover accuracy tests, shock formation and wave focusing.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement TBI-WAVES—H2020-MSCA-IF-2020 project No 101023950. Open access funding provided by IReL.peer-reviewe
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
A hyperbolic framework for shear sound beams in nonlinear solids
No full textIn soft elastic solids, directional shear waves are in general governed by coupled nonlinear KZK-type equations for the two transverse velocity components, when both quadratic nonlinearity and cubic nonlinearity are taken into account. Here we consider spatially two-dimensional wave fields. We propose a change of variables to transform the equations into a quasi-linear first-order system of partial differential equations. Its numerical resolution is then tackled by using a path-conservative MUSCL-Osher finite volume scheme, which is well-suited to the computation of shock waves. We validate the method against analytical solutions (Green¿s function, plane waves). The results highlight the generation of odd harmonics and of second-order harmonics in a Gaussian shear-wave beam.This work was supported by the Irish Research Council, Ireland under project ID GOIPD/2019/328. The authors thank the Irish Centre for High-End Computing (ICHEC) for the provision of computational facilities and support.peer-reviewe
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The KP equation of plane elastodynamics
No full textThe propagation of nonlinear and dispersive waves in various materials can be described by the well-known Kadomtsev–Petviashvili (KP) equation, which is a (2 + 1)-dimensional partial differential equation. In this paper, we show that the KP equation can be used to describe the in-plane motion of compressible elastic solids with dispersion. Furthermore, a modified KP equation with cubic nonlinearity is obtained in the case of incompressible solids with dispersion. Then, several solutions of these partial differential equations are discussed and computed using a Fourier spectral method. In particular, both equations admit solitary wave solutions.The work of the first author was supported by the European Union’s Horizon 2020 research and innovation programme grant TBI-WAVES - H2020-MSCA-IF-2020 project 101023950. The work of the third author was partially supported by the PRIN research project ‘The mathematics and mechanics of nonlinear wave propagation in solids’ grant 2022P5–R22A and by GNFM of Istituto Nazionale di Alta Matematica (INDAM).peer-reviewe
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