Simulation of natural convection with the Collocated Clustered Finite Volume scheme

International audienceThis paper presents numerical results obtained in the case of natural convection within non constant fluid density, using the Collocated Clustered Finite Volume (CCFV) scheme. The continuous equations are first given in a dimensionless form. Then we present the finite volume scheme with the principles and the spatial discretization used. Analytical tests illustrate the numerical behavior of this scheme according to the type of grid, of the pressure stabilization method and check the robustness of this scheme. Next, the results obtained on the square thermally driven cavity under large temperature differences show that the CCFV scheme accurately fits the reference results

Symbolic Possibilistic Logic: Completeness and Inference Methods

International audienceThis paper studies the extension of possibilistic logic to the case when weights attached to formulas are symbolic and stand for variables that lie in a totally ordered scale, and only partial knowledge is available on the relative strength of these weights. A proof of the soundness and the completeness of this logic according to the relative certainty semantics in the sense of necessity measures is provided. Based on this result, two syntactic inference methods are presented. The first one calculates the necessity degree of a possibilistic formula using the notion of minimal inconsistent sub-base. A second method is proposed that takes inspiration from the concept of ATMS. Notions introduced in that area, such as nogoods and labels, are used to calculate the necessity degree of a possibilistic formula. A comparison of the two methods is provided, as well as a comparison with the original version of symbolic possibilistic logic

A collocated finite volume scheme to solve free convection for general non-conforming grids

We present a new collocated numerical scheme for the approximation of the Navier-Stokes and energy equations under the Boussinesq assumption for general grids, using the velocity-pressure unknowns. This scheme is based on a recent scheme for the diffusion terms. Stability properties are drawn from particular choices for the pressure gradient and the non-linear terms. Numerical results show the accuracy of the scheme on irregular grids

Inventory of Beekeeping in the Algerian north (Tizi-ouzou and Bejaia)

The objective of this study is to make an inventory of the honey production in the counties of Bejaia and Tizi-Ouzou in northeastern Algeria. To achieve this, a survey was carried out on 31 beekeepers (14 in Bejaia and 17 in Tizi-Ouzou). The survey shows a social, cultural and religious role for 61.29% of the beekeepers. The beekeeping is primarily held by men (93.55%). It is the basic source of income for 64.52% of the respondents. The average age of the beekeepers is 42.90years (Min-Max: 28-67 years, Median: 40.5 years). The main products of the hive are honey (100%), swarms (16.13%), royal jelly (9.68%) and propolis (9.68%). The average honey production per hive is 7.70kg (Min-Max: 0.4-15kg hives, Median: 10kg). The average number of hives per beekeeper is 42.20 hives (Min-Max: 3-300 hives, Median: 17.50 hives). The average selling price of one kg of honey is 4000.00 DA / kg (Min-Max: 2000-5000DA; Median: 4000DA). The phenotype of the bee reported by 74.19% of the surveys is of small size with a long body and dark pigmentation corresponding to the breed “Apis mellifera intermissa”. Two apiculturists described another phenotype corresponding to the “Apis mellifera major”. The factors behind the motivations for beekeeping are consumption of honey (100%), income generation (90.32%), hobby (58.06%) and conservation of biodiversity (22.58%). The multiple constraints associated with several diseases, notably Varroase (mentioned by 80.65% of beekeepers), cause difficulties for the breeders. Thus they cannot profit maximum from beekeeping. Other constraints which were reported are; forest fires (35.48%), wasps (32.26%), absence of beekeeping professionals or technicians (29.03%), harsh and cold winters with snow (19.35%), high density of hives in the region (16.13%) and uncontrolled spreading of pesticides and crop protection products at farms (12.90%). The economic situation of the Algerian beekeepers can be optimized by improving the production potential of the local bees

Le boom pétrolier et le syndrome hollandais au Cameroun : symptômes et canaux de transmissions

Le poids du pétrole dans les exportations camerounaises a augmenté après sa découverte et la hausse de son prix au cours des années 1970. Une découverte du pétrole dans un pays en développement, conjuguée à une hausse de sa demande mondiale, conduit à l’expansion de sa production et d’une contraction de la taille des autres secteurs. Nous examinons dans ce mémoire l’impact qu’aura l’exploitation du pétrole camerounais sur l’économie du pays en présence du syndrome hollandais. Dans ce sens, la maladie hollandaise est principalement due à la découverte des ressources naturelles. L’augmentation de la demande mondiale de ces ressources augmente la demande mondiale de la devise nationale, ce qui provoquera l’appréciation du taux de change réel. Par conséquent, les autres secteurs se voient pénaliser. Pour vérifier la présence du syndrome hollandais et ses canaux de transmission, une approche par un modèle d’équilibre général calculable calibré sur les données de la matrice de la comptabilité sociale camerounaise de 2010 comprenant 42 secteurs d’activité. À ce titre, nous avons simulé une diminution progressive du prix à l’exportation du pétrole. Cette simulation devrait permettre de décrire la structure de l’économie camerounaise en absence d’une exploitation pétrolière importante. Notre simulation montre que le secteur agricole est avantagé alors que certains secteurs manufacturiers sont pénalisés. Mots clés : syndrome hollandais, désindustrialisation, modèle d’équilibre général calculable (MEGC), canaux de transmission, prix à l’exportation

Modélisation pluie-débit à l’échelle annuelle en Algérie du nord

La modélisation du comportement hydrologique des bassins versants est incontournable dès lors que l'on s'intéresse à des problématiques relatives à l’évaluation et la gestion optimale des ressources en eau. Ceci s’illustre par un aspect quantitatif, dans les pays comme l’Algérie où l’alimentation en eau est un facteur limitant. L’objectif principal de cet article est d’expliciter les relations entre les conditions hydrologiques et la disponibilité en eau de surface. A cet effet, un modèle pluie-débit à l’échelle annuelle qui prend en compte les paramètres physiques et climatiques a été mis au point. L’application porte sur l’Algérie du Nord dont la superficie est de 325 000 km2.La mise au point de ce modèle nécessite au préalable une base de données qui a été acquise lors des travaux antérieurs incluant la carte des pluies médianes, la carte des perméabilités et le modèle numérique de terrain. Afin de compléter cette base de données, la cartographie des pluies des différentes années pour lesquelles on dispose des débits a été réalisée en utilisant une méthodologie intitulée "cartographie de la pluie centrée réduite". Ainsi, les données de 467 postes pluviométriques ont été traitées et ont permis de tracer les cartes des isohyètes annuelles.L’étude de la relation pluie-débit à l’échelle annuelle est basée sur les données de débits de 50 stations hydrométriques réparties à travers la zone d’étude. La démarche utilisée s’est inspirée de la fonction de production du S.C.S (Soil Conservation Service). Les résultats du modèle après calage ont permis d’obtenir un coefficient d’explication de 0,75, ce qui signifie que 75 % de la variance est expliquée par la pluie moyenne, la surface et un coefficient (a) qui correspond à la pente moyenne des bassins versants.Modelling the hydrological behaviour of drainage basins is very important for solving problems related to the evaluation and optimal management of water resources. This is illustrated quantitatively in countries such as Algeria where water supply is a limiting factor. The principal aim of this paper was to explain the relationship between hydrological conditions and the availability of surface water. A model of rainfall-discharge was developed on a yearly scale, taking into account physical and climatic parameters. The application was carried out in northern Algeria where the total land surface is about 325 000 km2.The development of this model required a database, which was acquired during previous studies where maps of median rainfall and permeability as well as the digital elevation model were developed. In order to complete this database, the cartography of rainfall for the years for which we have discharge data was carried out using a methodology entitled "mapping standardized rainfall". To estimate and map annual rainfall, the kriging method was used. Two problems were encountered:- The presence of a drift highly altered the variogram and made it very difficult to infer a sub- structure function;- The variogram is significant only if the hypothesis of ergodicity is valid, which was not easy to assume for any given year.In order to resolve these difficulties, a homogeneous random and secondary stationary order function (same mean at all points and same covariance function) must be calculated. A previous study by ANRH (1993) allowed us to know the statistical parameters of the distribution at each point. These parameters were mapped, taking into consideration the topographical relief and distance to the sea. For every year and at each rainfall measure point, the standardized rainfall could be deduced. The correlogram gave information about the spatial variability of the phenomenon and its range, and subsequently the standardized rainfall was then interpolated. Annual rainfall was calculated by combining the grids of the means, the variances and the centered reduced rainfall (TOUAZI and LABORDE, 2000). Thus, the data of 467 rainfall gauges were used in order to create maps of the yearly isohyets.The rainfall-discharge relationship on an annual scale was based on 50 hydrometric stations distributed throughout the study area. The methodology used was derived from the production function of the S.C.S (Soil Conservation Service). This production function was part of modelling, which transformed total rainfall to net rainfall. This method was very representative of the natural hydrological processes. Indeed, it takes into account rainfall and the maximum infiltration capacity (S), which depends on the nature of the soil (lithology), vegetation and soil moisture content. In the current study, the basin surface and a regional parameter (a) were introduced in order to calibrate the model. This production function was implemented by supplying different values for the parameter (S). The values (n+1) were obtained by increasing the previous value (n) by 10 %. We evaluated the different values of (S) in the same way to obtain the last value (i). We calculated for these different values of the parameter (S) the square of the difference between the measured and estimated discharges for each year by measuring the discharge at different stations. For each station, we calculated the sum of these values for all the years and we retained the value of (S) that gave the minimal value. The results demonstrated that the values of (S) obtained were not significant because they tend to the infinite. For this reason, (S) was considered as a constant. In order to improve the model, we repeated the same operation, but instead of (S), we used the parameter (a) and performed the same calculation. After calibration of the model the results gave a coefficient of determination of 0.75, which means that 75 % of the variance was explained by the mean rainfall, the surface and the parameter (a).To explain the parameter (a), we calculated the correlation between its value at each station with the corresponding geology. This latter variable was characterized by the average storage capacity, which corresponds to the weighted average of the surfaces of the basin assigned to each permeability category (TOUAZI, 2001). The results demonstrated a coefficient of determination of 0.1. The correlation with the topographical relief was not necessary because it was taken into account in the cartography of the rainfall. We then proceeded to the cartography of the parameter (a). The results demonstrated an east-west gradient that was constant and a north-south gradient that decreased from north to south. With the digital elevation model, we used a geographical information system to deduce the slopes. For each basin, the average slope was calculated by taking the average of the values of the slopes of all the pixels that constituted the individual basin. The correlation between slopes and corresponding values of the parameter (a) gave a coefficient of correlation of 0.6.The results obtained by this model after calibration gave a coefficient of determination of 0.75, which means that 75% of the variance was explained by the mean rainfall, the surface and a coefficient (a), which corresponds to the average slope of the drainage basins

A Possibilistic Logic Approach to Conditional Preference Queries

International audienceThe paper presents a new approach to deal with database preference queries, where preferences are represented in the style of possibilistic logic, using symbolic weights. The symbolic weights may be processed without the need of a numerical assignment of priority. Still, it is possible to introduce a partial ordering among the symbolic weights if necessary. On this basis, four methods that have an increasing discriminating power for ranking the answers to conjunctive queries, are proposed. The approach is compared to different lines of research in preference queries including skyline-based methods and fuzzy set-based queries. With the four proposed ranking methods the first group of best answers is made of non dominated items. The purely qualitative nature of the approach avoids the commensurability requirement of elementary evaluations underlying the fuzzy logic methods

Numerical results using a colocated finite-volume scheme on unstructured grids for incompressible fluid flows

International audienceThis article presents numerical results using a new finite-volume scheme on unstructured grids for the incompressible Navier-Stokes equations. The discrete unknowns are the components of the velocity, the pressure, and the temperature, colocated at the centers Of the control volumes. The scheme is stabilized using an original method leading to local redistributions of the fluid mass, which simultaneously yields the control of the kinetic energy and the convergence of the scheme. Different comparisons with the literature (2-D and 3-D lid-driven cavity, backward-facing step, differentially heated cavity) allow us to assess the numerical properties of the scheme

La logique possibiliste avec poids symboliques : une preuve de complétude

International audienceOn considère une variante de la logique possibiliste, déjà proposée par Benferhat et coll., où les poids attachés aux formules sont remplacés par des variables symboliques à valeur sur une échelle totalement ordonnée. On suppose qu’on ne dispose que de contraintes de domination stricte entre ces poids inconnus. Dans ce cas, on peut étendre la sémantique et l’axiomatisation de la logique possibiliste, mais sa complétude nécessite une nouvelle preuve qui est décrite ici. La mise en oeuvre de cette logique peut exploiter des techniques de recherche de sousbases maximales consistantes et de raisonnement abductif

On the Semantics of Partially Ordered Bases

International audienceThis paper presents first results toward the extension of possibilistic logic when the total order on formulas is replaced by a partial preorder. Few works have dealt with this matter in the past but they include some by Halpern, and Benferhat et al. Here we focus on semantic aspects, namely the construction of a partial order on interpretations from a partial order on formulas and conversely. It requires the capability of inducing a partial order on subsets of a set from a partial order on its elements. The difficult point lies in the fact that equivalent definitions in the totally ordered case are no longer equivalent in the partially ordered one. We give arguments for selecting one approach extending comparative possibility and its preadditive refinement, pursuing some previous works by Halpern. It comes close to non-monotonic inference relations in the style of Kraus Lehmann and Magidor. We define an intuitively appealing notion of closure of a partially ordered belief base from a semantic standpoint, and show its limitations in terms of expressiveness, due to the fact that a partial ordering on subsets of a set cannot be expressed by means of a single partial order on the sets of elements. We also discuss several existing languages and syntactic inference techniques devised for reasoning from partially ordered belief bases in the light of this difficulty. The long term purpose is to find a proof method adapted to partially ordered formulas, liable of capturing a suitable notion of semantic closure