223 research outputs found
Intégration optimisée de composants virtuels orientés TDSI par la synthÚse d'architecture
- La complexité grandissante des SystÚmes sur Silicium (SoC) oblige les concepteurs à relever le niveau d'abstraction de leur description et à réutiliser des blocs fonctionnels préconçus, décrits au niveau RTL, de plus en plus complexes. La principale difficulté lors de la réutilisation de ce type de composants bas niveau provient de leur intégration (interfaçage avec le reste du systÚme). Dans le cadre du projet RNRT ALIPTA nous proposons d'une part de relever le niveau d'abstraction des descriptions en introduisant la notion de composant virtuel comportemental et d'autre part de générer un coeur d'IP RTL en synthétisant sous contraintes d'intégration sa description comportementale à l'aide d'outils de synthÚse haut niveau. Dans cet article nous rappelons briÚvement le flot de conception systÚme. Nous présentons les phases d'analyse garantissant la faisabilité de la synthÚse en fonction des contraintes algorithmiques de l'IP et d'intégration et abordons la modélisation de l'ensemble de contraintes. Nous présentons ensuite une expérience de réutilisation de composants virtuels pour le traitement de l'image avec un quantificateur initialement connecté à une DCT puis à une TO. Nous comparons les résultats obtenus en appliquant une méthode classique d'intégration de composant virtuel au niveau RTL par synthÚse d'un wrapper avec la méthode proposée
Fracture Propagation Driven by Fluid Outflow from a Low-permeability Aquifer
Deep saline aquifers are promising geological reservoirs for CO2
sequestration if they do not leak. The absence of leakage is provided by the
caprock integrity. However, CO2 injection operations may change the
geomechanical stresses and cause fracturing of the caprock. We present a model
for the propagation of a fracture in the caprock driven by the outflow of fluid
from a low-permeability aquifer. We show that to describe the fracture
propagation, it is necessary to solve the pressure diffusion problem in the
aquifer. We solve the problem numerically for the two-dimensional domain and
show that, after a relatively short time, the solution is close to that of
one-dimensional problem, which can be solved analytically. We use the relations
derived in the hydraulic fracture literature to relate the the width of the
fracture to its length and the flux into it, which allows us to obtain an
analytical expression for the fracture length as a function of time. Using
these results we predict the propagation of a hypothetical fracture at the In
Salah CO2 injection site to be as fast as a typical hydraulic fracture. We also
show that the hydrostatic and geostatic effects cause the increase of the
driving force for the fracture propagation and, therefore, our solution serves
as an estimate from below. Numerical estimates show that if a fracture appears,
it is likely that it will become a pathway for CO2 leakage.Comment: 21 page
Phase coexistence in consolidating porous media
The appearence of the fluid-rich phase in saturated porous media under the
effect of an external pressure is investigated. For this purpose we introduce a
two field second gradient model allowing the complete description of the
phenomenon. We study the coexistence profile between poor and rich fluid phases
and we show that for a suitable choice of the parameters non-monotonic
interfaces show-up at coexistence
Recursive double-size fixed precision arithmetic
International audienceThis work is a part of the SHIVA (Secured Hardware Immune Versatile Architecture) project whose purpose is to provide a programmable and reconfigurable hardware module with high level of security. We propose a recursive double-size fixed precision arithmetic called RecInt. Our work can be split in two parts. First we developped a C++ software library with performances comparable to GMP ones. Secondly our simple representation of the integers allows an implementation on FPGA. Our idea is to consider sizes that are a power of 2 and to apply doubling techniques to implement them efficiently: we design a recursive data structure where integers of size 2^k, for k>k0 can be stored as two integers of size 2^{k-1}. Obviously for k<=k0 we use machine arithmetic instead (k0 depending on the architecture)
A stabilized finite element method for finite-strain three-field poroelasticity
We construct a stabilized finite-element method to compute flow and finitestrain
deformations in an incompressible poroelastic medium. We employ a three-
field mixed formulation to calculate displacement, fluid flux and pressure directly
and introduce a Lagrange multiplier to enforce flux boundary conditions. We use
a low order approximation, namely, continuous piecewise-linear approximation
for the displacements and fluid flux, and piecewise-constant approximation for
the pressure. This results in a simple matrix structure with low bandwidth. The
method is stable in both the limiting cases of small and large permeability. Moreover,
the discontinuous pressure space enables efficient approximation of steep
gradients such as those occurring due to rapidly changing material coefficients or
boundary conditions, both of which are commonly seen in physical and biological
applications
A conduit dilation model of methane venting from lake sediments
Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L06408, doi:10.1029/2011GL046768.Methane is a potent greenhouse gas, but its effects on Earth's climate remain poorly constrained, in part due to uncertainties in global methane fluxes to the atmosphere. An important source of atmospheric methane is the methane generated in organic-rich sediments underlying surface water bodies, including lakes, wetlands, and the ocean. The fraction of the methane that reaches the atmosphere depends critically on the mode and spatiotemporal characteristics of free-gas venting from the underlying sediments. Here we propose that methane transport in lake sediments is controlled by dynamic conduits, which dilate and release gas as the falling hydrostatic pressure reduces the effective stress below the tensile strength of the sediments. We test our model against a four-month record of hydrostatic load and methane flux in Upper Mystic Lake, Mass., USA, and show that it captures the complex episodicity of methane ebullition. Our quantitative conceptualization opens the door to integrated modeling of methane transport to constrain global methane release from lakes and other shallow-water, organic-rich sediment systems, and to assess its climate feedbacks.This work was supported
by the U.S. Department of Energy (grants DEâFC26â06NT43067
and DEâAI26â05NT42496), an NSF Doctoral Dissertation Research grant
(0726806), a GSA Graduate Student Research grant, and MIT Martin, Linden
and Ippen fellowships
Stochastic particle packing with specified granulometry and porosity
This work presents a technique for particle size generation and placement in
arbitrary closed domains. Its main application is the simulation of granular
media described by disks. Particle size generation is based on the statistical
analysis of granulometric curves which are used as empirical cumulative
distribution functions to sample from mixtures of uniform distributions. The
desired porosity is attained by selecting a certain number of particles, and
their placement is performed by a stochastic point process. We present an
application analyzing different types of sand and clay, where we model the
grain size with the gamma, lognormal, Weibull and hyperbolic distributions. The
parameters from the resulting best fit are used to generate samples from the
theoretical distribution, which are used for filling a finite-size area with
non-overlapping disks deployed by a Simple Sequential Inhibition stochastic
point process. Such filled areas are relevant as plausible inputs for assessing
Discrete Element Method and similar techniques
Numerical study of nonlinear heat transfer from a wavy surface to a high permeability medium with pseudo-spectral and smoothed particle methods
Motivated by petro-chemical geological systems, we consider the natural convection boundary layer flow from a vertical isothermal wavy surface adjacent to a saturated non-Darcian high permeability porous medium. High permeability is considered to represent geologically sparsely packed porous media. Both Darcian drag and Forchheimer inertial drag terms are included in the velocity boundary layer equation. A high permeability medium is considered. We employ a sinusoidal relation for the wavy surface. Using a set of transformations, the momentum and heat conservation equations are converted from an (x, y) coordinate system to an (x,η) dimensionless system. The two-point boundary value problem is then solved numerically with a pseudo-spectral method based on combining the BellmanâKalaba quasi linearization method with the Chebyschev spectral collocation technique (SQLM). The SQLM computations are demonstrated to achieve excellent correlation with smoothed particle hydrodynamic (SPH) Lagrangian solutions. We study the effect of Darcy number (Da), Forchheimer number (Fs), amplitude wavelength (A) and Prandtl number (Pr) on the velocity and temperature distributions in the regime. Local Nusselt number is also computed for selected cases. The study finds important applications in petroleum engineering and also energy systems exploiting porous media and undulating (wavy) surface geometry. The SQLM algorithm is shown to be exceptionally robust and achieves fast convergence and excellent accuracy in nonlinear heat transfer simulations
An experimental and constitutive investigation on the chemo-mechanical behaviour of a clay
- âŠ