86,527 research outputs found
Peridynamic simulation of elastic wave propagation by applying the boundary conditions with the surface node method
No full textPeridynamics is a novel nonlocal theory able to deal with discontinuities, such as crack initiation and propagation. Near the boundaries, due to the incomplete nonlocal region, the peridynamic surface effect is present, and its reduction relies on using a very small horizon, which ends up being expensive computationally. Furthermore, the imposition of nonlocal boundary conditions in a local way is often required. The surface node method has been proposed to solve both the aforementioned issues, providing enhanced accuracy near the boundaries of the body. This method has been verified in the cases of quasi-static elastic problems and diffusion problems evolving over time, but it has never been applied to a elastodynamic problems. In this work, we show the capabilities of the surface node method to solve a peridynamic problem of elastic wave propagation in a homogeneous body. The numerical results converge to the corresponding peridynamic analytical solution under grid refinement and exhibit no unphysical fluctuations near the boundaries throughout the whole timespan of the simulation
A peridynamic model for oxidation and damage in zirconium carbide ceramics
No full textZirconium carbide (ZrC) has potential to be applied in next-generation nuclear reactors for space missions and industrial applications. The mechanisms controlling ZrC oxidation dependence on temperature, material composition, pressure, porosity are not fully understood. In this work, we use a peridynamic modeling of diffusion/reaction across several regions observed in previous experiments to explain the oxygen diffusion mechanism and reaction kinetics. We emphasize the importance in the oxidation and damage process of a transition layer of partially-oxidized ZrC. The peridynamic model has an autonomously moving oxidation interface, and the delamination/detachment of oxide (induced by large volumetric expansion) is simulated here with an oxygen concentration-driven damage model. Once the diffusion properties are calibrated to match the measured oxygen concentration across the oxidation front, the speed of propagation of the oxidation front is predicted by a 1D peridynamic model in excellent agreement with experimental observations. An extension to 2D finds the shape of remaining unoxidized ZrC conforming to experimental observations
Moving interfaces in peridynamic diffusion models and the influence of discontinuous initial conditions: Numerical stability and convergence
No full textWe derive numerical stability conditions and analyze convergence to analytical nonlocal solutions of 1D peridynamic models for transient diffusion with and without a moving interface. In heat transfer or oxidation, for example, one often encounters initial conditions that are discontinuous, as in thermal shock or sudden exposure to oxygen. We study the numerical error in these models with continuous and discontinuous initial conditions and determine that the initial discontinuities lead to lower convergence rates, but this issue is present at early times only. Except for the early times, the convergence rates of models with continuous and discontinuous initial conditions are the same. In problems with moving interfaces, we show that the numerical solution captures the exact interface location well, in time. These results can be used in simulating a variety of reaction-diffusion type problems, such as the oxidation-induced damage in zirconium carbide at high temperatures
A peridynamics elastoplastic model with isotropic and kinematic hardening for static problems
No full textThis study proposes a formulation equivalent to J2 plasticity with the associated flow rule to simulate the elastoplastic behavior of materials with isotropic or kinematic hardening in a peridynamic framework. The capabilities of the developed formulation are analysed through 2D and 3D case studies whose results (displacement and stress field) are compared with those obtained from the corresponding FEM models
Linearized state-based peridynamics for 2-D problems
No full textthis work, the authors formulate a 2-D linearized ordinary state-based peridynamic model of elastic deformations and compute the stiffness matrix for 2-D plane stress/strain conditions. This model is then verified by testing the recovery of elastic properties for given Poisson’s ratios in the range 0.1–0.45. The convergence behavior of peridynamic solutions in terms of the size of the nonlocal region by comparison with the classical (local) mechanics model is also discussed. The degree to which the peridynamic surface effect influences the recovery of elastic properties is examined, and stress/strain recovery values are found to have a definite influence on the results. The technique used here can provide the basis for applying 2-D peridynamic models to the study of fatigue failure and quasi-static fracture proble
Variations on the Author
No full text“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
[Newspaper Clipping: Author Claims Evidence of Second JFK Assassin #1]
No full textNewspaper article titled "Author Claims Evidence of Second JFK Assassin." The article states that author Richard J. Whalen concluded "that there is circumstantial evidence to support the theory of a second assassin in the shooting of President John F. Kennedy.
Also By The Same Author: AKTiveAuthor, a Citation Graph Approach to Name Disambiguation
No full textThe desire for definitive data and the semantic web drive for inference over heterogeneous data sources requires co-reference resolution to be performed on those data. In particular, name disambiguation is required to allow accurate publication lists, citation counts and impact measures to be determined. This paper describes a graph-based approach to author disambiguation on large-scale citation networks. Using self-citation, co-authorship and document source analyses, AKTiveAuthor clusters papers, achieving precision of 0.997 and recall of 0.818 over a test group of eight surname clusters
John F. Kennedy telegram to Roosevelt
No full textJersey Homesteads (later the Borough of Roosevelt) was established in the 1930s as an agro-industrial cooperative community. It was established specifically for urban Jewish garment workers, many of whom had emigrated from Europe. President John F. Kennedy sent a telegram to the citizens of Roosevelt, New Jersey, apologizing for not being able to attend the memorial dedication in honor of former President Franklin Delano Roosevelt. (Jersey Homesteads became Roosevelt in 1945 in honor of the president.) President Kennedy expressed his gratitude to the people of Roosevelt for constructing the memorial, and commented that it will serve as a constant reminder of Roosevelt's good works
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