The Experts below are selected from a list of 6522 Experts worldwide ranked by ideXlab platform
Antony Jameson - One of the best experts on this subject based on the ideXlab platform.
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a new class of high order energy stable flux reconstruction schemes for triangular elements
Journal of Scientific Computing, 2012Co-Authors: Patrice Castonguay, P E Vincent, Antony JamesonAbstract:The flux reconstruction (FR) approach allows various well-known high-order schemes, such as collocation based nodal discontinuous Galerkin (DG) methods and spectral difference (SD) methods, to be cast within a single unifying framework. Recently, the authors identified a new class of FR schemes for 1D conservation laws, which are simple to implement, efficient and guaranteed to be linearly stable for all orders of accuracy. The new schemes can easily be extended to quadrilateral elements via the construction of tensor product bases. However, for triangular elements, such a construction is not possible. Since numerical simulations over complicated geometries often require the computational domain to be tessellated with simplex elements, the development of stable FR schemes on simplex elements is highly desirable. In this article, a new class of energy stable FR schemes for triangular elements is developed. The schemes are parameterized by a single Scalar Quantity, which can be adjusted to provide an infinite range of linearly stable high-order methods on triangular elements. Von Neumann stability analysis is conducted on the new class of schemes, which allows identification of schemes with increased explicit time-step limits compared to the collocation based nodal DG method. Numerical experiments are performed to confirm that the new schemes yield the optimal order of accuracy for linear advection on triangular grids.
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a new class of high order energy stable flux reconstruction schemes
Journal of Scientific Computing, 2011Co-Authors: P E Vincent, Patrice Castonguay, Antony JamesonAbstract:The flux reconstruction approach to high-order methods is robust, efficient, simple to implement, and allows various high-order schemes, such as the nodal discontinuous Galerkin method and the spectral difference method, to be cast within a single unifying framework. Utilizing a flux reconstruction formulation, it has been proved (for one-dimensional linear advection) that the spectral difference method is stable for all orders of accuracy in a norm of Sobolev type, provided that the interior flux collocation points are located at zeros of the corresponding Legendre polynomials. In this article the aforementioned result is extended in order to develop a new class of one-dimensional energy stable flux reconstruction schemes. The energy stable schemes are parameterized by a single Scalar Quantity, which if chosen judiciously leads to the recovery of various well known high-order methods (including a particular nodal discontinuous Galerkin method and a particular spectral difference method). The analysis offers significant insight into why certain flux reconstruction schemes are stable, whereas others are not. Also, from a practical standpoint, the analysis provides a simple prescription for implementing an infinite range of energy stable high-order methods via the intuitive flux reconstruction approach.
C. Hansen - One of the best experts on this subject based on the ideXlab platform.
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Interactive volume rendering using multi-dimensional transfer functions and direct manipulation widgets
2005Co-Authors: J. Kniss, Gordon Kindlmann, C. HansenAbstract:Most direct volume renderings produced today employ one- dimensional transfer functions, which assign color and opacity to the volume based solely on the single Scalar Quantity which com- prises the dataset. Though they have not received widespread atten- tion, multi-dimensional transfer functions are a very effective way to extract specific material boundaries and convey subtle surface properties. However, identifying good transfer functions is difficult enough in one dimension, let alone two or three dimensions. This paper demonstrates an important class of three-dimensional transfer functions for Scalar data (based on data value, gradient magnitude, and a second directional derivative), and describes a set of direct manipulation widgets which make specifying such transfer func- tions intuitive and convenient. We also describe how to use modern graphics hardware to interactively render with multi-dimensional transfer functions. The transfer functions, widgets, and hardware combine to form a powerful system for interactive volume explo- ration
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Multidimensional transfer functions for interactive volume rendering
IEEE Transactions on Visualization and Computer Graphics, 2002Co-Authors: J. Kniss, Gordon Kindlmann, C. HansenAbstract:Most direct volume renderings produced today employ 1D transfer functions which assign color and opacity to the volume based solely on the single Scalar Quantity which comprises the data set. Though they have not received widespread attention, multi-dimensional transfer functions are a very effective way to extract materials and their boundaries for both Scalar and multivariate data. However, identifying good transfer functions is difficult enough in 1D, let alone 2D or 3D. This paper demonstrates an important class of 3D transfer functions for Scalar data, and describes the application of multi-dimensional transfer functions to multivariate data. We present a set of direct manipulation widgets that make specifying such transfer functions intuitive and convenient. We also describe how to use modern graphics hardware to both interactively render with multidimensional transfer functions and to provide interactive shadows for volumes. The transfer functions, widgets and hardware combine to form a powerful system for interactive volume exploration.
J. Kniss - One of the best experts on this subject based on the ideXlab platform.
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Interactive volume rendering using multi-dimensional transfer functions and direct manipulation widgets
2005Co-Authors: J. Kniss, Gordon Kindlmann, C. HansenAbstract:Most direct volume renderings produced today employ one- dimensional transfer functions, which assign color and opacity to the volume based solely on the single Scalar Quantity which com- prises the dataset. Though they have not received widespread atten- tion, multi-dimensional transfer functions are a very effective way to extract specific material boundaries and convey subtle surface properties. However, identifying good transfer functions is difficult enough in one dimension, let alone two or three dimensions. This paper demonstrates an important class of three-dimensional transfer functions for Scalar data (based on data value, gradient magnitude, and a second directional derivative), and describes a set of direct manipulation widgets which make specifying such transfer func- tions intuitive and convenient. We also describe how to use modern graphics hardware to interactively render with multi-dimensional transfer functions. The transfer functions, widgets, and hardware combine to form a powerful system for interactive volume explo- ration
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Multidimensional transfer functions for interactive volume rendering
IEEE Transactions on Visualization and Computer Graphics, 2002Co-Authors: J. Kniss, Gordon Kindlmann, C. HansenAbstract:Most direct volume renderings produced today employ 1D transfer functions which assign color and opacity to the volume based solely on the single Scalar Quantity which comprises the data set. Though they have not received widespread attention, multi-dimensional transfer functions are a very effective way to extract materials and their boundaries for both Scalar and multivariate data. However, identifying good transfer functions is difficult enough in 1D, let alone 2D or 3D. This paper demonstrates an important class of 3D transfer functions for Scalar data, and describes the application of multi-dimensional transfer functions to multivariate data. We present a set of direct manipulation widgets that make specifying such transfer functions intuitive and convenient. We also describe how to use modern graphics hardware to both interactively render with multidimensional transfer functions and to provide interactive shadows for volumes. The transfer functions, widgets and hardware combine to form a powerful system for interactive volume exploration.
T L Kim - One of the best experts on this subject based on the ideXlab platform.
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anomalous scaling of a passive Scalar advected by the navier stokes velocity field two loop approximation
Physical Review E, 2005Co-Authors: Ts L Adzhemyan, N V Antonov, Juha Honkonen, T L KimAbstract:The field theoretic renormalization group and operator-product expansion are applied to the model of a passive Scalar Quantity advected by a non-Gaussian velocity field with finite correlation time. The velocity is governed by the Navier-Stokes equation, subject to an external random stirring force with the correlation function proportional to $\ensuremath{\delta}(t\ensuremath{-}{t}^{\ensuremath{'}}){k}^{4\ensuremath{-}d\ensuremath{-}2\ensuremath{\epsilon}}$. It is shown that the Scalar field is intermittent already for small $\ensuremath{\epsilon}$, its structure functions display anomalous scaling behavior, and the corresponding exponents can be systematically calculated as series in $\ensuremath{\epsilon}$. The practical calculation is accomplished to order ${\ensuremath{\epsilon}}^{2}$ (two-loop approximation), including anisotropic sectors. As for the well-known Kraichnan rapid-change model, the anomalous scaling results from the existence in the model of composite fields (operators) with negative scaling dimensions, identified with the anomalous exponents. Thus the mechanism of the origin of anomalous scaling appears similar for the Gaussian model with zero correlation time and the non-Gaussian model with finite correlation time. It should be emphasized that, in contrast to Gaussian velocity ensembles with finite correlation time, the model and the perturbation theory discussed here are manifestly Galilean covariant. The relevance of these results for real passive advection and comparison with the Gaussian models and experiments are briefly discussed.
Filippo Berto - One of the best experts on this subject based on the ideXlab platform.
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fatigue failure transition analysis in load carrying cruciform welded joints based on strain energy density approach
Fatigue & Fracture of Engineering Materials & Structures, 2017Co-Authors: Wei Song, Xuesong Liu, Filippo Berto, P Wang, H FangAbstract:This paper details a study of the application of notch stress intensity theory to the fatigue failure mode analysis of the transition in load-carrying cruciform welded joints. The weldment fatigue crack initiation point is difficult to predict precisely because it usually occurs in the vicinity of the weld toe or weld root. To investigate the relationship between fatigue failure location and the geometry of the weldments, we analysed the weld toe and root asymptotic notch stress fields were analysed using the notch stress intensity factors on the basis of the Williams' solution in Linear Elastic Fracture Mechanics (LEFM). Numerous configurations of cruciform joints of various plate thicknesses, transverse plate thickness, weld sizes and incomplete penetration size were used to investigate the location of the fatigue failure. The strain energy density (SED) surrounding the notch tip was introduced to unify the Scalar Quantity and preclude the inconsistency of the dimensionality of the notch stress intensity factors for various notch opening angles. The results of the investigation showed that the SED approach can be used to determine the transition zone for a variety of joint geometries. The validity of the SED criteria was verified by comparing the experimental results of this study with the complied results for load-carrying cruciform welded joints reported in literature.
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tensile fracture analysis of blunt notched pmma specimens by means of the strain energy density
Engineering Solid Mechanics, 2015Co-Authors: Alberto Campagnolo, Filippo BertoAbstract:Article history: Received September 6, 2014 Accepted 12 November 2014 Available online 12 December 2014 In this paper, a volume criterion based on a simple Scalar Quantity, the mean value of the strain energy (SED), has been used to assess the static strength of notched components made of Polymethylmethacrylate (PMMA). The local-strain-energy based approach has been applied to a well-documented set of experimental data recently reported in the literature. Data refer to blunt U-notched cylindrical specimens of commercial PMMA subjected to static loads and characterised by a large variability of notch tip radius (from 0.67 mm to 2.20 mm). Critical loads obtained experimentally have been compared with the theoretical ones, estimated by keeping constant the mean value of the strain energy in a well-defined small size volume. In addition, some new tests dealing with V-notched specimens with end holes have been carried out to investigate the effect of the notch opening angle. © 2015 Growing Science Ltd. All rights reserved.
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local strain energy density and fatigue strength of welded joints under uniaxial and multiaxial loading
Engineering Fracture Mechanics, 2008Co-Authors: P Lazzarin, Filippo Berto, Paolo Livieri, Michele ZappalortoAbstract:Abstract In the notch stress intensity approach to the fatigue assessment of welded joints, the weld toe is modelled as a sharp V-notch and the local stress distributions in plane problems are given on the basis of the relevant mode I and mode II notch stress intensity factors (N-SIFs). These factors quantify the magnitude of asymptotic stress distribution obeying Williams’ solution. If the V-notch opening angle at the weld toe is constant and the mode II is not singular, the mode I N-SIF can be directly used to summarize the fatigue behaviour of welded joints. In all the other cases, varying the V-notch angle or including multiaxial loading conditions (where typically both Mode I and Mode III stress distributions are singular), the synthesis can be carried out on the basis of the mean value of the strain energy density over a well-defined volume surrounding the weld toe or the weld root. By using this Scalar Quantity, two fatigue scatterbands are obtained for structural steels and aluminium alloys, respectively. The material-dependent radius RC of the control volume (area) is carefully identified with reference to conventional arc welding processes. Sometimes the weld toe radius is found to be very different from zero. The local strain energy approach can be extended as it stands also to these cases, providing a gradual transition from a N-SIF-based approach to a Kt-based approach.
