1,720,967 research outputs found
Nonconforming Dirichlet boundary conditions in implicit material point method by means of penalty augmentation
Get PDFIn many geomechanics applications, material boundaries are subjected to large displacements and deformation. Under these circumstances, the application of boundary conditions using particle methods, such as the material point method (MPM), becomes a challenging task since material boundaries do not coincide with the background mesh. This paper presents a formulation of penalty augmentation to impose nonhomogeneous, nonconforming Dirichlet boundary conditions in implicit MPM. The penalty augmentation is implemented utilizing boundary particles, which can move either according to or independently from the material deformation. Furthermore, releasing contact boundary condition, as well as the capability to accommodate slip boundaries, is introduced in the current work. The accuracy of the proposed method is assessed in both 2D and 3D cases, by convergence analysis reaching the analytical solution and by comparing the results of nonconforming and classical grid-conforming simulations
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Stabilized Material Point Method for Hydro-Mechanical Coupled Problems in Geomechanics
Get PDFUnderstanding of fluid behavior in fluid-saturated porous media has been a challenging research problem tackled through theoretical, experimental, and numerical approaches over many decades. Modeling such multiphysics phenomena, in both small and large deformation regimes, requires careful consideration of numerical accuracy and stability to achieve reliable results. This study employs the Material Point Method (MPM), a hybrid Eulerian-Lagrangian approach that can simulate large deformation problems involving history-dependent materials. The dissertation's contributions can be divided into two main application areas: (i) deep geomechanical well analysis under fluid injection and extraction, and (ii) surficial geotechnical structures involving the nonlinear interaction of free-surface flow and deformable porous media.First, a new approach called CutMesh MPM is introduced for small-deformation solid mechanics. This method improves standard MPM discretization by re-evaluating quadrature weights and incorporating explicit boundary discretization to better track evolving surface geometry and apply boundary conditions. Algorithms for boundary detachment, detection, and reconstruction are introduced to track the evolution of wellbore geometry due to material detachment. The efficacy of the approach is validated through numerical studies of dry boreholes under anisotropic loading. Building on this, the study extends the CutMesh MPM framework to hydro-mechanical analysis of saturated boreholes. The coupled formulation integrates a two-phase single-point MPM formulation, assuming a fractional-step method, for accurate analysis of fluid extraction and injection in poroelastic and poro-elasto-plastic materials.The second part of the dissertation focuses on modeling free-surface fluid dynamics, seepage, and interactions with porous solids. A mixed MPM formulation is introduced to address challenges related to the numerical instability of incompressible fluid flow. Several stabilization strategies are proposed and utilized to enhance the simulation's robustness and accuracy. This formulation is verified and validated through extensive numerical tests on complex fluid dynamics problems. Additionally, a unified approach integrating the Navier-Stokes and Darcy-Brinkman-Forchheimer equations is proposed to model flows in both non-porous and porous domains. This method uses the blurred interface technique to improve numerical stability at the interface, as demonstrated in a range of 1D, 2D, and 3D benchmarks. Finally, the mixed MPM is extended to account for strongly coupled hydro-mechanical problems through a three-field formulation involving solid displacement, fluid displacement, and pressure. The proposed approach features stabilized discretization methods and consistent derivations, with preliminary results in three-dimensional consolidation problems demonstrating its potential
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
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
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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