644 research outputs found
Comparison of methods for curvature estimation from volume fractions
This paper evaluates and compares the accuracy and robustness of curvature
estimation methods for three-dimensional interfaces represented implicitly by
discrete volume fractions on a Cartesian mesh. The height function (HF) method
is compared to three paraboloid fitting methods: fitting to the piecewise
linear interface reconstruction centroids (PC), fitting to the piecewise linear
interface reconstruction volumetrically (PV), and volumetrically fitting (VF)
the paraboloid directly to the volume fraction field. The numerical studies
presented in this work find that while the curvature error from the VF method
converges with second-order accuracy as with the HF method for static
interfaces represented by exact volume fractions, the PV method best balances
low curvature errors with low computational cost for dynamic interfaces when
the interface reconstruction and advection are coupled to a two-phase
Navier-Stokes solver
Pierre Petit, History, Memory, and the Territorial Cults in the Highlands of Laos. The Past inside the Present
Commencées en 2003, les enquêtes de terrain et les recherches en archives dont ce livre est l’aboutissement portent sur une petite vallée du Nord-Est du Laos, dans la province de Houaphan. Elles concernent un groupe de villages habités par différentes populations de langue tai (Lao, Tai « Noirs » et Tai « Rouges »), présentes également dans la province vietnamienne voisine de Son La. Outre la grande richesse des données recueillies par Pierre Petit et ses collègues de l’Université nationale d..
Geophysical investigation of the Pb-Zn deposit of Lontzen-Poppelsberg, Belgium
The drillhole information from the Lontzen-Poppelsberg site has demonstrated three orebodies and has allowed the estimation of the extension of the lodes, their dip, and the location at the ground surface. The localisation of the lodes makes them excellent targets for further exploration with geophysics. This deposit is classified as a Mississippi Valley Type (MVT) deposit. It consists mainly of Pb-Zn-Fe sulphides that display contrasting values in resistivity, chargeability, density, and magnetic susceptibility, with regards to the sedimentary host rocks. The dipole-dipole direct current (DC) resistivity and induce polarization (IP) profiles have been collected and inverted to successfully delineate the Pb-Zn mineralization and the geological structures. Short-spacing EM34 electromagnetic conductivity data were collected mainly on the top of Poppelsberg East lode and have revealed a conductive body matching with the geologically modelled mineralization. Gravity profiles have been carried out perpendicularly to the lode orientation; they show a strong structural anomaly. High resolution ground magnetic data were collected over the study area, but they showed no anomaly over the ore deposits. The geophysical inversion results are complementary to the model based on drill information, and allow us to refine the delineation of the mineralization. The identification of the geophysical signatures of this deposit permits targeting new possible mineralization in the area
Le groupe ACROE-ICA : recherche et formation en art, sciences et technologies
International audienceLe groupe ACROE-laboratoire ICA est reconnu dans le monde scientifique et dans le monde artistique pour être à l'origine de plusieurs concepts et techniques fondateurs et innovants sur la manière d'aborder le rôle de l'ordinateur et plus généralement les technologies numériques dans la création artistique. Depuis 30 ans, le groupe mène et soutient ses activités de recherche, de création et de formation au cøeur de l'interdisciplinarité Arts, Sciences, et Technologies
Simulating interfacial flows: a farewell to planes
Over the past decades, the volume-of-fluid (VOF) method has been the method
of choice for simulating atomization processes, owing to its unique ability to
discretely conserve mass. Current state-of-the-art VOF methods, however, rely
on the piecewise-linear interface calculation (PLIC) to represent the interface
used when calculating advection fluxes. This renders the estimated curvature of
the transported interface zeroth-order accurate at best, adversely impacting
the simulation of surface-tension-driven flows.
In the past few years, there have been several attempts at using
piecewise-parabolic interface approximations instead of piecewise-linear ones
for computing advection fluxes, albeit all limited to two-dimensional cases or
not inherently mass conservative. In this contribution, we present our most
recent work on three-dimensional piecewise-parabolic interface reconstruction
and apply it in the context of the VOF method. As a result of increasing the
order of the interface representation, the reconstruction of the interface and
the estimation of its curvature now become a single step instead of two
separate ones. The performance of this new approach is assessed both in terms
of accuracy and stability and compared to the classical PLIC-VOF approach on a
range of canonical test-cases and cases of surface-tension-driven
instabilities
Introduction
“(...) -a lonely planet but a crowded stage”. Victor Alneng (2002 : 127) Depuis plusieurs décennies, on assiste un peu partout dans le monde à un développement sans précédent de la mobilité touristique impliquant des flux à la fois humains, techniques, financiers et culturels. Longtemps, deux attitudes ont prévalu au sein des sciences sociales, notamment francophones, à l’égard de ce phénomène. La première considérait le tourisme comme un objet mineur, sinon trivial; la seconde y voyait la si..
Proper Orthogonal Decomposition Analysis and Modelling of the wake deviation behind a squareback Ahmed body
We investigate numerically the 3-D flow around a squareback Ahmed body at Reynolds number Re = 104. Proper Orthogonal Decomposition (POD) is applied to a symmetry-augmented database in order to describe and model the flow dynamics. Comparison with experiments at a higher Reynolds number in a plane section of the near-wake at mid-height shows that the simulation captures several features of the experimental flow, in particular the antisymmetric quasi-steady deviation mode. 3-D POD analysis allows us to classify the different physical processes in terms of mode contribution to the kinetic energy over the entire domain. It is found that the dominant fluctuating mode on the entire domain corresponds to the 3-D quasi-steady wake deviation, and that its amplitude is well estimated from 2-D near-wake data. The next most energetic flow fluctuations consist of vortex shedding and bubble pumping mechanisms. It is found that the amplitude of the deviation is negatively correlated with the intensity of the vortex shedding in the spanwise direction and the suction drag coefficient. Finally, we find that despite the slow convergence of the decomposition, a POD-based low-dimensional model reproduces the dynamics of the wake deviation observed experimentally, as well as the main characteristics of the global modes identified in the simulation
Fluid force and symmetry breaking modes of a 3D bluff body with a base cavity
International audienceA cavity at the base of the squareback Ahmed model at Re 4 Ă— 10 5 is able to reduce the base suction by 18% and the drag coefficient by 9%, while the geometry at the separation remains unaffected. Instantaneous pressure measurements at the body base, fluid force measurements and wake velocity measurements are investigated varying the cavity depth from 0 to 35% of the base height. Due to the reflectional symmetry of the rectangular base, there are two Reflectional Symmetry Breaking (RSB) mirror modes present in the natural wake that switch from one to the other randomly in accordance with the recent findings of Grandemange et al. (2013b). It is shown that these modes exhibit an energetic 3D static vortex system close to the base of the body. A sufficiently deep cavity is able to stabilize the wake toward a symmetry preserved wake, thus suppressing the RSB modes and leading to a weaker elliptical toric recirculation. The stabilization can be modelled with a Langevin equation. The plausible mechanism for drag reduction with the base cavity is based on the interaction of the static 3D vortex system of the RSB modes with the base and their suppression by stabilization. There are some strong evidences that this mechanism may be generalized to axisym-metric bodies with base cavity
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