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

SOS-Églises : à la rescousse de notre patrimoine religieux dans le sud-ouest de l’Ontario

Il y a dix ans, personne ne se doutait que deux petits villages canadiens-français bien tranquilles du sud-ouest de l’Ontario, Pointe-aux-Roches et Saint-Joachim, étaient sur le point de vivre une aventure qui allait leur donner une notoriété provinciale, sinon nationale. Une aventure les mettant aux prises avec des autorités religieuses et politiques qui ont fait l’erreur de tenir pour acquis leur docile acceptation du retrait d’un élément important de leur identité : leur patrimoine religieux. André Chénier raconte cette histoire d’une poignée de gens qui (sans potion magique aucune!) a trouvé la force et les moyens de dire… non

Needs, supports, burden, and affect the experiences of family members of individuals with mental illness

The purpose of this research project was to examine the needs and supports of family members of people with schizophrenia and to determine the relationship between needs, supports, objective burden, negative affect, and positive affect. The participants were 32 family members of a self-help and support group catering to the families of people with schizophrenia. Three categories of needs and supports were examined. These three categories included: problem-solving, financial and tangible assistance, and social-emotional needs and supports. Family members discussed: the degree of need and support, who currently meets the need, issues and concerns, and suggestions about who might best meet the needs and how. Family members experienced greater need than support across all three categories. Family members themselves and the community self-help and support group were key resources. Issues and concerns focused on the aspects of need that must be addressed in order for programs and policies to be successful. Suggestions about who might best meet the need and how revealed that family members have a clear understanding of existing problems and have clear solutions about how to address their needs. Another aspect of the action-oriented strategies of this study was a discussion of other themes. These themes were not directly related to specific needs but to groups of needs. Again, clear and practical suggestions were made about how to address these issues at a community level. Theoretical questions examined the relationship between needs and supports, on the one hand, and affect and stress on the other hand. Positive and negative affect were independent of each other. Negative affect was directly related to the level of financial and tangible assistance needs. Social-emotional support was directly related to positive affect and inversely related to negative affect. There was no evidence that needs and supports interacted to predict objective burden, positive affect, or negative affect consistent with the stress-buffering hypothesis. The implications for future research center on attempting to provide an optimal “fit” between need and support in community-based agencies. Existing programs should be evaluated to determine if programs meet the needs of those who make use of the programs. If supports are in place, stress can be reduced. Programs should provide support as a part of service delivery. Researchers should focus on making use of mental health users and family members to elicit their ideas about program design, implementation and methods for providing support

PREDICTING THE SEQUENCE OF MEAN PROPULSION FORCES DURING INDOOR WHEELCHAIR SPORTS: A PROOF OF CONCEPT

Monitoring the push force is an important asset during wheelchair (WC) sports training. However, current instrumented wheels cannot be used without significantly altering the WC-user dynamics. Moreover, the push force could not be estimated directly from the WC acceleration because of the strong influence of the upper body movement on the WC-user dynamics. In this paper, we present a new method to predict the progression of the mean push force using temporal information (grab/release times) and kinematic information (WC velocity changes). This method was validated at two velocities with 17 manual WC users who propelled their own standard manual WC in an indoor hallway. When summed over both sides, the root-mean-square prediction error was 15.7 N at a comfortable velocity and 35.9 N at the maximum velocity. These results have great implications for indoor WC sports training

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

Stability of free convection in air-filled horizontal annuli: influence of the radius ratio

International audienceLinear stability of two-dimensional natural convection in air-filled horizontal annuli is numerically investigated for radius ratios in the range 1.2 less than or equal to R less than or equal to 3 and for Rayleigh numbers less than 10(4). Bifurcation diagrams are obtained for various radius ratios and the main thresholds are tracked as a function of R. A new instability mode has been highlighted which breaks the symmetry of the basic flow. This result demonstrates the need of modeling the annular gap without assuming flow symmetry. In addition to bifurcation maps drawn in the Rayleigh number-radius ratio plane, a map of possible flow patterns is also established. This map allows to foresee the number of solutions and the corresponding flow structures. (C) 2004 Elsevier Ltd. All rights reserved

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

Stability analysis of natural convective flows in horizontal annuli: effects of axial and radial aspect ratios

International audienceLinear stability analyses for two-dimensional natural convection in horizontal air-filled annuli are performed for three-dimensional perturbations and radius ratios in the range 1.2 ≤ R ≤ 3. Flow transitions from moderate to large gap annuli, which have not been reported before, are thoroughlyinvestigated. As a result, stability diagrams are obtained for finite and for infinite length annuli. The leading disturbances and threshold values are found to agree well with experimental data and three-dimensional numerical solutions. Three-dimensional simulations were also carried out toexamine the influence on the flow stability of no-slip boundary conditions at the end walls

Agrégation d'un grand nombre de petites charges en incluant l'incertitude de la disponibilité des ressources

Le réseau électrique en continuel changement demande une gestion des ressources efficace pour assurer sa stabilité. Avec la nouvelle technologie de communication et les nouvelles ressources d’énergie renouvelables, la gestion du réseau électrique fait face à de nombreux défis. On anticipe une croissance de l’utilisation de la voiture électrique dans les années à venir. Si la recharge des voitures ne se fait pas de façon intelligente, on pourra observer une forte croissance de la demande énergétique en heure de pointe. Grâce à des programmes de Gestion de la demande (Demand Response (DR)), les clients peuvent adapter leur consommation d’électricité en échange d’incitatifs. Une requête de DR envoyée à un client lui permet d’adapter sa consommation d’électricité selon les besoins de l’utilité. Les producteurs d’électricité sont appelés utilités dans cette recherche. Les secteurs résidentiel et commercial offrent un grand potentiel pour les programmes de DR, car ensemble ces secteurs représentent près d’un tiers de la consommation totale. Bien que ces secteurs offrent un grand potentiel, l’exploitation de ceux-ci comporte également de grands défis. Un grand nombre de clients consommant de petites charges doivent être gérés efficacement. C’est pourquoi les agrégateurs sont introduits en tant qu’intermédiaires entre l’utilité et les consommateurs. Le rôle des agrégateurs est de faire la gestion des programmes de DR avec les clients. Grâce à eux, les requêtes de DR sont distribuées parmi les clients dans le but de satisfaire la requête d’utilité. La requête d’utilité quant à elle est une commande de réduction ou d’augmentation de la consommation globale dans le but d’équilibrer la production et la consommation d’électricité. Le problème connu de répartition économique est utilisé comme référence pour développer le modèle mathématique de distribution des requêtes de DR. Ce problème de base est trivial à résoudre et ne comporte pas de complexité. Par contre, la difficulté résulte du fait qu’il existe une certaine probabilité qu’un client ne réponde pas à la requête de DR. Lorsqu’un client répond à une requête, cela signifie que le client adapte sa consommation selon la requête. S’il ne répond pas à la requête, cela signifie qu’il n’adapte pas sa consommation. L’agrégateur doit donc distribuer plus de requêtes de DR pour pallier l’incertitude de la réponse. L’objectif de cette recherche est de modéliser un problème mathématique réaliste de l’agrégateur en incluant l’incertitude de la réponse des clients. Le modèle est résolu trois fois par jour pendant une semaine. Les résolutions sont interreliées pour éviter d’envoyer les requêtes de DR toujours aux mêmes clients. Comme les requêtes de DR requièrent un coût, l’agrégateur doit faire une distribution de façon à minimiser ses coûts tout en assurant le respect de la requête d’utilité.----------Abstract The grid has changed a lot over the years. New technologies of communication and renewable production have arisen and create new challenges for the grid. We expect a higher penetration of electric vehicles in the next years. The increase use of electric vehicles can cause a large demand during peak times and have to be managed effectively. The utility can now communicate with the customers in real time. Utilities can have access to the load consumption information through smart meter. New technologies allow a new type of resources called Demand Response (DR). DR programs send requests to the customers to adapt their load consumption. The objective of the DR programs is to fit the load consumption curve to the production curve. The balance between the production and the consumption is essential to the stability of the grid. To do so, the customers adapt their load consumption according to DR requests. The load consumption can be reduced by a smart thermostat or smart water heater. It can also be shifted during off-peak periods with the charge or discharge of electric vehicles. To help the utility to dispatch DR requests among the customers, aggregators are introduced. Aggregators act as intermediaries between the utility and the customers. They receive an incentive and utility request from the utility and distribute DR requests and incentives to customers. DR requests are defined by the load in kW to reduce, to increase or to shift. Their objective is to maximize their own profit. This research focuses on formulating an optimization problem of the aggregators. They aim to reduce the total load consumption during peak periods or to increase the total load consumption when the renewable production is high. In this research, 21 resolutions are made per week, three per day during peak times. The resolutions are interconnected to avoid the overuse of the same clients. The optimization model is based on the Economic Dispatch problem which is trivial to solve. The model dispatches DR requests among the customers while minimizing the total cost of the aggregator. The utility request has to be satisfied in order to keep the stability of the grid. The complexity of the problem comes with the uncertainty of the response of the clients. In the literature, this uncertainty is not included in the aggregator optimization problem. Several external factors influence the responsiveness of the clients like the time of the day, the day of the week, the frequency of the requests and the direction of the requests. When a client respond to the DR request, it means that the load consumption has been changed according to the request. Otherwise, the load consumption is unchanged and the client does not respond to the request. This uncertainty has to be included in the model to make it more realistic