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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Comportement mécanique instantané des structures hybrides GFRP-béton / Mechanical Behavior of GFRP-Concrete hybrid Structures

Koaik, Alaa 08 September 2017 (has links)
L'utilisation des composites dans la construction des bâtiments ou des ouvrages d'art est de plus en plus importante car ces matériaux présentent des atouts indiscutables comme un très bon rapport performance / poids ou une facilité de mise en oeuvre. Cependant, leur essor est ralenti par certaines faiblesses dont l'une des plus importantes est leur souplesse qui induit des déplacements élevés et des risques d'instabilités importants qui ne permettent pas d'exploiter tout le potentiel de ces matériaux. Dans le cas d'éléments de structure fléchis, une des solutions consiste à associer les profilés composites à une dalle en béton armé. La connexion est établie par des butées mécaniques, par collage, ou l'association des deux. L'objectif général de ce travail est d'étudier le comportement des structures mixtes GFRP-Béton fléchies sous chargement statique instantané : Cette étude comporte un volet expérimental lourd et un volet de modélisation numérique. Elle a été abordée à 3 échelles : matériaux, interface, et structure. Trois modes de connexion ont été exploités. Sur le plan expérimental, nous avons d'abord caractérisé tous les matériaux utilisés : composite, béton, adhésif, acier des armatures et des connecteurs. Puis, la caractérisation à l'échelle de l'interface a été effectuée par l'essai push-out dans différentes configurations (7 séries d'essais au total). Enfin, le comportement à l'échelle d'éléments de structure a été étudié sur des mono-poutres pour des portées allant de 2 m à 4.8 m, sur des poutres composites seules ou sur des poutres mixtes (10 poutres au total). Une passerelle bi-poutre de 4.8 m de portée a également été testée dans la même configuration et jusqu'à la ruine. La modélisation du comportement de ces poutres hybrides a été effectuée selon 2 cas théoriques. Elles ont d'abord été modélisées dans le cadre de la théorie des poutres multicouches, dans le domaine élastique et à l'approche de la ruine. Selon le mode de connexion, le glissement à l'interface est pris en compte ou négligé. Ces poutres ont également été modélisées par la MEF en utilisant des éléments volumiques et en considérant une connexion parfaite. Les résultats d'essais montrent le comportement correspondant à chaque mode de connexion : la connexion par butées mécaniques simples est à ce jour celle qui s'avère la plus efficace. Les écarts modèle / calculs restent acceptables sauf à proximité de l'interface où les déformations peuvent être affectées par la fissuration du béton qui reste difficile à prédire de façon précise. La simulation numérique donne des valeurs très proches de la réalité et répond aux questions posées lors de l'expérience / Advanced composites are increasingly used in construction thanks to their indisputable advantages such as high strength to weight ratio and ease of implementation. However, their growth is hindered by a main weak point: low stiffness. Advanced composites risk instabilities under high loads which make it not possible to exploit their full potential. Considering flexural elements, one of the solutions proposed consists in associating the composite profiles with a reinforced concrete slab. The connection of both materials is either established by bolting, bonding or a combination of both techniques.In this study, 3 different connection modes were tested on structural elements with different spans. Previously, to characterize the mechanical behavior of the interface, 35 push out specimens having bolted or bonded connections were prepared and tested. In addition, all materials used were characterized.A composite beam (Pu1) and 8 hybrid beams (PB1-PB8) were tested under 3 points bending up to failure. The results are exploited to construct and test a hybrid footbridge. 7 push out series were tested and digital image correlation was used to analyze the behavior at the interface and measure the displacement fields to determine the slip. Concrete, GFRP, bolts, the adhesive and the concrete reinforcing steel bars were all characterized.The experimental data obtained from the tests is compared to calculation results obtained by a multi-layer beam model within service limit states and at ultimate ones. Besides, a 3D finite element model was developed to provide more accurate results.The results allow distinguishing 3 behavior modes relative to the 3 connection types: the connection by mechanical studs proves to be the most efficient so far. The measurements are also compared to the results obtained by a multi-layer beam model. The differences are acceptable except in the vicinity of the interface where the deformations can be affected by the cracking of the concrete which remains difficult to predict precisely. The 3D simulations present with an excellent agreement the experiments and explain some observations obtained
22

Rotator assembly at Indexator

Lundström, Jonathan, Hörnberg, Emil January 2017 (has links)
The thesis is concerning rotator assembly at Indexator. A need to increase production has been seen and it can be done by implementing an optimized assembly process. In addition to the assembly process a new design on workstations and new test equipment is needed.The study resulted into three assembly process proposals. The processes were balanced, layouts were produced and Plant simulation was utilized to produce simulation models. Each proposal were analyzed based on cost, performance, ease of implementation, flexibility and worker condition. This resulted in a stationary assembly process being most promising and a 3D simulation model was produced for visualization and better understanding. The stationary assembly process has a capacity for 90 rotators per day, while reducing the amount of workers by one.The layout of the workstations was done based on the assembly process layout and further developed to make the work cell lean and ergonomic. It resulted in three workstations to perform the assembly. The test bench was developed by creating target specifications, establish a test procedure and decide components for the test bench layout. The finished test bench can measure dynamic torque, count particles to ensure cleanliness and is able to run the test unattended. / Examensarbetet handlar om montering av rotatorer på Indexator. Målet är att ta fram en optimerad monteringsprocess som kan implementeras i Indexators fabrik utan svårigheter. Den nya monteringsprocessen kommer kräva en ny design på arbetsstationerna och nya testbänkar.Fyra koncept på monteringsprocessen togs fram, baserat på monteringens behov och målsättning. Efter utvärdering så modifierades de fyra koncepten till tre förslag på monteringsprocesser. Processerna balancerades, layouter utvecklades och simuleringsmodeller producerades för varje process. Varje förslag analyserades baserat på kostnad, prestanda, implementation,flexibilitet och arbetar-förhållande. Resultatet blev en stationär monteringsprocess och en 3Dsimulering gjordes för visualisering och förståelse. Den stationära monteringsprocessen har en kapacitet på 90 rotatorer per dag och reducerar behovet av montörer.Layouten för monteringsstationerna baseras på processens layout och har modifierats för ergonomiska aspekter. Inom monteringsstationerna så utvecklades layouten för att minimera antalet onödiga rörelser för montören. Testriggens design utvecklades genom att analysera de behov som fanns, skapa en kravspecifikation samt utvärdera och besluta om testprocedur, upplägg för testrigg och dess ingående komponenter. Testriggen uppfyller målsättningen som är att kunna mäta dynamiskt vridmoment, räkna partiklar för att säkerställa renhet i rotatorn och kunna utföra testningen självgående för att frigöra montören under testprogrammet.
23

Výpočetní analýza chování aktivní zóny tlakovodního jaderného reaktoru pomocí kódu PARCS / Computational analysis of pressurized water reactor core behaviour using PARCS code

Novotný, Filip January 2014 (has links)
The Master Thesis performs search concerning advanced small and medium power light-water reactors’ designs, including different possibilities to gain a license for their development and operation. The work covers the principal theory about the area of neutronics calculations, principal equations and simplifications. There are several different methods for solution of neutronics calculations. The thesis gives an overview of two principal groups of codes – deterministic methods and Monte Carlo method. The survey shows computational codes examples based on mentioned methods. The computational code PARCS is chosen for further study, which contained description of the input and output file, process of the model creation and conditions for neutronics calculation the of selected reactor design. Based on these facts, the transient calculation has been prepared within the thesis. Thee analyses are described – reactor emergency shutdown, reactor shutdown with stuck group of control and emergency shutdown rods and reactor shutdown with faulty reaction of emergency shutdown rods.
24

Modelová studie účinků ultrazvuku na vývoj plodu / Model Study of Ultrasound Effects on Fetal Development

Jaroš, Josef January 2009 (has links)
The progress in ultrasound techniques goes hand in hand with increasing of diagnostic machine acoustic outputs. Ultrasound biological effects can adversely influence the development of human fetus. Recent studies of thermal effect on biological tissues are usually based on simulation of simple ultrasound transducers. The aim of this work is to build a flexible model of diagnostic system to simulate temperature increase during fetal development. Different types of ultrasound probes were used for generation of acoustic field with simulated piezoelectric element properties. Optimized linear and phased arrays were modeled with dynamic beam steering and focus. Computer simulations were concentrated on extreme conditions in obstetric ultrasonography and 3D tissue model was compared with real ultrasound probes measurements. To detect temperature increase, the bone tissue phantom was used. Results point out potential risks for fetus with diagnostic ultrasound probes. Based on the results of this work, practical recommendations increasing safety of obstetric examinations were drawn.

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