Solar induced ventilation in the Algerian and similar climates

In hot climates ventilation can be a useful means of cooling dwellings, if the outside air be cooler than that inside the dwelling. Often, in hot regions the outside air is so hot during the day that cooling by ventilation is of no benefit until the evening when the outside air gets cooler. Ventilation can then be beneficial, and can be promoted by a sun-warmed cavity or 'solar chimney' added to a building on the sunward side. The cavity may be of any material of high thermal capacity. Heat from the sun is stored within the walls forming the cavity and heats the air within. The cavity is closed at the top and bottom by dampers. These, when opened in the evening, allow the buoyant hot air contained within to rise, drawing cooler outside air into the building. This process continues until the stored energy is consumed. The performance of a typical cavity to induce ventilation into a house is studied experimentally and theoretically. The measurements are made on a full-scale model in the steady state. Cavity width and air inlet area to the cavity are important parameters in this study. Measurements are made on the temperature and velocity of the air. Observations on air flow patterns in the room and the cavity are made. A steady state analysis is compared with the measurements. A dynamic model is developed based on a finite difference technique, and used to examine the performance of the cavity in various circumstances. The results show that air movement can be produced by a sun-warmed cavity if the dimensions of inlet and cavity width are kept at certain values

Finite element analysis of steel beams with web apertures under fire condiction

This work is intended to analyse the behaviour steel beams with apertures under high temperatures rise due to fire using finite elements simulations with ANSYS software. It includes a structural fire analysis and a comparative study of cellular and castellated steel beams which takes into account transient temperature effect, material and geometric non-linear behaviour. FE models which estimate limiting time, mid-span deflection and failure temperature are presented for hexagonal and circular types of web opening shapes under several uniform load levels. The study shows that for any beam with closely spaced openings failure in fire will in most cases be caused by failure of the steel web. The numbers of web-openings and cells as well as their shapes are critical for the behaviour of castellated sections and cellular beams under fire condition.info:eu-repo/semantics/publishedVersio

Effect of Rosemary and Oregano Aqueous Extracts Supplementation on Microbial Growth during Refrigerated Storage of Milk

The aim of the present study is to evaluate the effect of adding rosemary and oregano aqueous extracts to raw cow milk on the dynamics of microbial growth during milk refrigeration. The aqueous extracts from plants leaves were prepared and supplemented to milk samples at different concentrations: 0, 0.25, 0.5, 0.75 and 1 mg mL-1 for rosemary and 0, 1.25, 2.5, 3.75, 5 mg mL-1 for oregano. The evolution of microbial growth was monitored at regular intervals of times during ten days of refrigerated storage at 4 °C. The enumeration of the microbial flora was conducted by the culture methods. The supplementation of the two plants extracts to refrigerated milk generated a prolongation of the lag phase duration and limited microbial growth. For rosemary, the lag phase length (λ) in milks without supplementation (0 mg mL-1) was prolonged from 1.2 ± 0.80 day (28.8 h) to 1.66 ± 0.92 day (39.84 h) in milks added with 0.75 and 1 mg mL-1 while the maximum cell load (Xmax) diminished from 7.00 ± 0.17 log CFU mL-1 in non-supplemented milks to 6.56 ± 0.19 log CFU mL-1 in milks added with the same concentrations. For oregano, λ was delayed from 4.12 ± 0.11 day (98.88 h) in milks without supplementation to 5.04 ± 0.97 day (120.96 h) in milks added with 1.25 mg mL-1. A decrease of Xmax was remarked for the whole of the concentrations, registering the lowest value of 4.45 ± 1.34 log CFU mL-1 at 2.5 and 3.75 mg mL-1. The use of rosemary and oregano aqueous extracts as natural additives during refrigeration could offer opportunities as biopreservatives in the milk industry, to reduce heat pretreatment and the addition of chemical additives

Effect of Rosemary and Oregano Aqueous Extracts Supplementation on Microbial Growth during Refrigerated Storage of Milk

The aim of the present study is to evaluate the effect of adding rosemary and oregano aqueous extracts to raw cow milk on the dynamics of microbial growth during milk refrigeration. The aqueous extracts from plants leaves were prepared and supplemented to milk samples at different concentrations: 0, 0.25, 0.5, 0.75 and 1 mg mL-1 for rosemary and 0, 1.25, 2.5, 3.75, 5 mg mL-1 for oregano. The evolution of microbial growth was monitored at regular intervals of times during ten days of refrigerated storage at 4 °C. The enumeration of the microbial flora was conducted by the culture methods. The supplementation of the two plants extracts to refrigerated milk generated a prolongation of the lag phase duration and limited microbial growth. For rosemary, the lag phase length (λ) in milks without supplementation (0 mg mL-1) was prolonged from 1.2 ± 0.80 day (28.8 h) to 1.66 ± 0.92 day (39.84 h) in milks added with 0.75 and 1 mg mL-1 while the maximum cell load (Xmax) diminished from 7.00 ± 0.17 log CFU mL-1 in non-supplemented milks to 6.56 ± 0.19 log CFU mL-1 in milks added with the same concentrations. For oregano, λ was delayed from 4.12 ± 0.11 day (98.88 h) in milks without supplementation to 5.04 ± 0.97 day (120.96 h) in milks added with 1.25 mg mL-1. A decrease of Xmax was remarked for the whole of the concentrations, registering the lowest value of 4.45 ± 1.34 log CFU mL-1 at 2.5 and 3.75 mg mL-1. The use of rosemary and oregano aqueous extracts as natural additives during refrigeration could offer opportunities as biopreservatives in the milk industry, to reduce heat pretreatment and the addition of chemical additives

Diagnostic de systèmes complexes par comparaison de listes d’alarmes : application aux systèmes de contrôle du LHC

In the context of the CERN Large Hadron Collider (LHC), a large number of control systems have been built based on industrial control and SCADA solutions. Beyond the complexity of these systems, a large number of sensors and actuators are controlled which make the monitoring and diagnostic of these equipment a continuous and real challenge for human operators. Even with the existing SCADA monitoring tools, critical situations prompt alarms avalanches in the supervision that makes diagnostic more difficult. This thesis proposes a decision support methodology based on the use of historical data. Past faults signatures represented by alarm lists are compared with the alarm list of the fault to diagnose using pattern matching methods. Two approaches are considered. In the first one, the order of appearance is not taken into account, the alarm lists are then represented by a binary vector and compared to each other thanks to an original weighted distance. Every alarm is weighted according to its ability to represent correctly every past faults. The second approach takes into account the alarms order and uses a symbolic sequence to represent the faults. The comparison between the sequences is then made by an adapted version of the Needleman and Wunsch algorithm widely used in Bio-Informatic. The two methods are tested on artificial data and on simulated data extracted from a very realistic simulator of one of the CERN system. Both methods show good results.Au CERN (Organisation européenne pour la recherche nucléaire), le contrôle et la supervision du plus grand accélérateur du monde, le LHC (Large Hadron Collider), sont basés sur des solutions industrielles (SCADA). Le LHC est composé de sous-systèmes disposant d’un grand nombre de capteurs et d’actionneurs qui rendent la surveillance de ces équipements un véritable défi pour les opérateurs. Même avec les solutions SCADA actuelles, l’occurrence d’un défaut déclenche de véritables avalanches d’alarmes, rendant le diagnostic de ces systèmes très difficile. Cette thèse propose une méthodologie d’aide au diagnostic à partir de données historiques du système. Les signatures des défauts déjà rencontrés et représentés par les listes d’alarmes qu’ils ont déclenchés sont comparées à la liste d’alarmes du défaut à diagnostiquer. Deux approches sont considérées. Dans la première, l’ordre d’apparition des alarmes n’est pas pris en compte et les listes d’alarmes sont représentées par un vecteur binaire. La comparaison se fait à l’aide d’une distance pondérée. Le poids de chaque alarme est évalué en fonction de son aptitude à caractériser chaque défaut. La seconde approche prend en compte l’ordre d’apparition des alarmes, les listes d’alarmes sont alors représentées sous forme de séquences symboliques. La comparaison entre ces deux séquences se fait à l’aide d’un algorithme dérivé de l’algorithme de Needleman et Wunsch utilisé dans le domaine de la Bio-Informatique. Les deux approches sont testées sur des données artificielles ainsi que sur des données extraites d’un simulateur très réaliste d’un des systèmes du LHC et montrent de bons résultats

Finite element analysis of steel beams with web apertures under fire condiction

This work is intended to analyse the behaviour steel beams with apertures under high temperatures rise due to fire using finite elements simulations with ANSYS software. It includes a structural fire analysis and a comparative study of cellular and castellated steel beams which takes into account transient temperature effect, material and geometric non-linear behaviour. FE models which estimate limiting time, mid-span deflection and failure temperature are presented for hexagonal and circular types of web opening shapes under several uniform load levels. The study shows that for any beam with closely spaced openings failure in fire will in most cases be caused by failure of the steel web. The numbers of web-openings and cells as well as their shapes are critical for the behaviour of castellated sections and cellular beams under fire condition.info:eu-repo/semantics/publishedVersio

Connection of a Steel Column Base Plate: Mechanical Behavior and Stiffening Effects

This paper investigates the behaviour of a steel column base connection subjected to a bending moment and compressive axial force. The behaviour of this connection is quite complex due to the number of components, such as the base plate, anchor rods, and stiffeners, to be considered in the numerical models. Moreover, a nonlinear three-dimensional finite element model was used to simulate the column base connection. This model can be used to analyze the moment-rotation relationship for the connection through the validation of numerical modeling with those given by the experimental test results and compared with the analytical model based on the components method of Eurocode 3. It was shown that in addition to the stiffness and bending resistance of the column base connection, other mechanical parameters, such as moment-rotation shape, stress distribution, and prying actions, can be significantly influenced by changing the properties of the components. It has been demonstrated that the anchor rod is not only affected by the axial force but also by a local moment that is not taken into consideration by the analytical model of Eurocode3. An extensive parametric study on stiffeners showed very interesting effects obtained by adding the welded stiffeners to the column base connections. Doi: 10.28991/CEJ-2022-08-09-02 Full Text: PD

Etude par simulation numérique du comportement des portiques métalliques en situation d’incendie

Les structures en portiques métalliques à double versants sont largement utilisées dans les bâtiments industriels pour des raisons pratiques d’exploitation, de durabilité et de rentabilité. Cependant le matériau acier quoi que ductile, il reste vulnérable aux excès de températures. Les récents événements d’incendies concernant les structures et bâtiments industriels de Sonatrach, à Alger dans une zone urbaine ou à Skikda dans une zone industrielle, nous rappellent le danger réel et le risque potentiel des incendies. Les nouvelles normes Européennes définissent des exigences actives et passives concernant le comportement au feu des hangars industriels. L’objectif de ce travail est d’étudier, par des simulations numériques, le comportement des portiques métalliques à double versants sous différents scénarios d’incendie. L’analyse numérique par la MEF et utilisant le logiciel ANSYS est considérée afin d’évaluer la résistance de ces structures et de rationaliser leur protection au feu. Une analyse, utilisant les non linéarités géométrique et matérielle, est conduite avec une variation progressive des températures jusqu’à la ruine. Différents taux de chargement ainsi que différents scénarios de feu seront utilisés pour évaluer la température critique ainsi que les déplacements des portiques en fonction de l’évolution de la température. Les résultats du modèle numérique sont comparés à ceux calculés par les méthodes simplifiées de l’Eurocode 3info:eu-repo/semantics/publishedVersio