DEM simulations on spherical materials have been performed to study the behaviour of model granular materials not only under monotonous stress path such as triaxial compression or extension, but also under two-way cycling loading paths. Three reference states have been considered to characterize the behaviour of the granular material: the characteristic state, transitory state between volumetric contraction and dilation, the state of maximum resistance and the critical state. These states are regarded with respect to void ratio and anisotropy of fabric which are the two internal variables retained for the description of the internal state of the material. The characteristic state and the state at maximum resistance are clearly dependent on both levels of density and anisotropy at the beginning of a loading path. Bilinear models involving the two internal variables were designed for the characteristic state, the maximum dilatancy and the extent of the dilatancy domain for axisymetric loadings. They show that in each case the effect of density and anisotropy are different in compression and extension. The influence of anisotropy and density seems to be of the same order of magnitude. Copyright © 2009 John Wiley & Sons, Ltd.
martes, 20 de octubre de 2009
Numerical local analysis of relevant internal variables for constitutive modelling of granular materials
DEM simulations on spherical materials have been performed to study the behaviour of model granular materials not only under monotonous stress path such as triaxial compression or extension, but also under two-way cycling loading paths. Three reference states have been considered to characterize the behaviour of the granular material: the characteristic state, transitory state between volumetric contraction and dilation, the state of maximum resistance and the critical state. These states are regarded with respect to void ratio and anisotropy of fabric which are the two internal variables retained for the description of the internal state of the material. The characteristic state and the state at maximum resistance are clearly dependent on both levels of density and anisotropy at the beginning of a loading path. Bilinear models involving the two internal variables were designed for the characteristic state, the maximum dilatancy and the extent of the dilatancy domain for axisymetric loadings. They show that in each case the effect of density and anisotropy are different in compression and extension. The influence of anisotropy and density seems to be of the same order of magnitude. Copyright © 2009 John Wiley & Sons, Ltd.
Global and local central non-upwind finite volume schemes for hyperbolic conservation laws in porous media
The focus of this paper is on the development of convective flow approximation schemes that offer the benefits of an upwind formalism without actually upwinding. Development of robust schemes that remove or reduce upwind dependence would represent a significant step forward leading to a fundamental simplification of current methods for flow in porous media and reservoir simulation. Copyright © 2009 John Wiley & Sons, Ltd.
Hunting for rhythm's DNA: Computational geometry unlocks a musical phylogeny
(PhysOrg.com) -- Does Bo Diddley rule the world? Though he died last year, the iconic singer and guitarist of American blues and rock still rules the rhythms of the world, says computer scientist Godfried Toussaint. Toussaint uses complex algorithms to ferret where the rhythms of world music came from - in the same way an evolutionary biologist might hunt for the origins of, say, an arthropod body part.
Interpolation and Iteration for Nonlinear Filters. (arXiv:0910.3241v1 [math.NA])
We present a general form of the iteration and interpolation process used in
implicit particle filters. Implicit filters are based on a pseudo-Gaussian
representation of posterior densities, and are designed to focus the particle
paths so as to reduce the number of particles needed in nonlinear data
assimilation. Examples are given.
Hamiltonian Boundary Value Methods (Energy Conserving Discrete Line Integral Methods). (arXiv:0910.3621v1 [math.NA])
Recently, a new family of integrators (Hamiltonian Boundary ValueMethods) has
been introduced, which is able to precisely conserve the energy function of
polynomial Hamiltonian systems and to provide a practical conservation of the
energy in the non-polynomial case. We settle the definition and the theory of
such methods in a more general framework. Our aim is on the one hand to give
account of their good behavior when applied to general Hamiltonian systems and,
on the other hand, to find out what are the optimal formulae, in relation to
the distribution of the nodes. Such analysis is based upon the notion of
extended collocation conditions and the definition of discrete line integral,
and is carried out by looking at the limit of such family of methods as the
number of the so called silent stages tends to infinity.
Inversion of the Laplace transform from the real axis using an adaptive iterative method. (arXiv:0910.3385v1 [math.NA])
In this paper a new method for inverting the Laplace transform from the real
axis is formulated. This method is based on a quadrature formula. We assume
that the unknown function $f(t)$ is continuous with (known) compact support. An
adaptive iterative method and an adaptive stopping rule, which yield the
convergence of the approximate solution to $f(t)$, are proposed in this paper.
U2 concert to be streamed live on YouTube
Irish rock megastars U2 announced Monday that their upcoming concert at the Pasadena Rose Bowl in California will be streamed live on YouTube.
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