L’objectif de ce travail est de réaliser des suspensions aqueuses d’alumine, écoresponsables, dont le comportement rhéologique est adapté à la mise en forme par coulage en bande. En effet, les suspensions utilisées dans le procédé de coulage en bande sont classiquement composées d’une poudre céramique, d’un solvant, d’un dispersant, d’un liant et d’un plastifiant. Ces additifs sont généralement des polymères issus de la pétrochimie susceptibles de présenter des risques pour la santé de l’opérateur et/ou pour l’environnement (en particulier avec les solvants organiques). Ces travaux visent donc de substituer tous les additifs venant de la pétrochimie par des additifs écoresponsables, ne présentant aucun risque pour la santé de l’opérateur et pour l’environnement. Les travaux menés dans le cadre de cette thèse ont alors permis d’identifier des polymères naturels extraits de plantes comme des candidats prometteurs pour le remplacement des additifs organiques classiques. Puis, l’étude des interactions entre ces bio-polymères et l’alumine a mené au développement d’un protocole spécifique adapté à la formulation de suspensions d’alumine à base de ces bio-molécules. Ainsi, à l’aide de ce protocole, des suspensions aqueuses ont été réalisées avec ces additifs écoresponsables qui ont abouti à la réalisation de bandes crues facilement manipulables et ne présentant ni craquelures, ni bulles. Enfin, les densités après frittage obtenues sont proches des valeurs rencontrées dans la littérature / The aim of this work is focused on the elaboration of new alumina suspensions with biopolymer additives and rheological properties adapted to the tape casting process. The suspensions used in the tape casting process are basically composed of a ceramic powder, a solvent, a dispersant, a binder and a plasticizer. These additives are usually polymers coming from the petrochemical sector which show risks for the operator health or the environment (in particular with organic solvents). Thus, natural polymers extracted from plants were identified as promising candidates in order to substitute the classical organic additives. Then, the study of the interactions between different organic additives with alumina led to a specific protocol for the formulation of aqueous alumina suspensions with these bio-polymers. Then, mechanical properties of the green and sintered tapes were evaluated in relation with the nature of bio-polymer additives. The obtained densities are close to the values reported in the litterature

Growing numbers of suspensions and expulsions of students with disabilities (SWDs) have prompted school districts to explore nonpunitive alternatives to traditional suspension practices. The study school district implemented nonpunitive alternatives to suspension for SWDs, specifically students classified as emotionally disturbed (ED). SWDs are being suspended at a higher rate than their general education peers for the same violation. The purpose of this causal-comparative study was to examine differences in academic performance between students with emotional disabilities who received out of school suspensions and those who received nonpunitive consequences other than suspension for the same violation. To understand disruptive behavior, social learning theory provided the framework for this study. The sample included 20 high school students, grades 9-12, who were SWD eligible under the criteria of ED. Archival data included academic records, attendance records, and suspension records. To compare the means of the data, independent-samples t tests were used to analyze differences in grade point average between the groups. The results found that with nonpunitive alternatives, student attendance was improved; however, there was no significant difference found in academic performance between students who received nonpunitive consequences and those who received out of school suspension. Statistical power was limited due to the study sample size. Positive social change implications include providing initial research findings to the study school district and initiating the dialogue on reducing suspensions of SWDs to improve attendance, which may increase the potential for future academic success.

This thesis revisits the concept of ground vehicles active suspensions system from a power harvesting perspective. I introduce the two dimensions of freedom quarter vehicle model for calculations of vehicle dynamics as well as a road profile model based on PSD classifications based on International Organization for Standardization’s technical document, ISO 8608 “Mechanical vibration -- Road surface profiles -- Reporting of measured data”. I report the power harvesting potential of the conventional viscous fluid dampers for an extensive range of road profile roughness indices and vehicle speeds. I explain the problem of additional power harvesting from the regenerative electric damper operating in the "dead-zone" and introduce Pulse Width Modulated (PWM) DC-DC converter as a solution. I analyze the efficiency of this system by circuit level simulations in PSpice. / Graduate / 0540 / 0544 / farhang@uvic.ca

Zugl.: Stuttgart, Univ., Diss., 2008

Nous avons étudié expérimentalement la mise en suspension de particules lorsque l’on injecte du gaz à la base d’une couche de grains immergée dans un liquide, en géométrie confinée (cellule de Hele-Shaw). En configuration verticale, le système atteint toujours un régime stationnaire résultant de la compétition entre l’entraînement des grains par la remontée des bulles, et leur sédimentation. Un modèle phénoménologique permet d’expliquer les propriétés de la suspension ainsi formée, et du lit granulaire non affecté par la remontée de gaz. L’effet de la gravité effective dans le système est ensuite considérée. Lorsqu’un état stationnaire existe, la taille du lit granulaire présente un maximum pour un angle d’inclinaison de la cellule de 30-40 degrés environ. Cette observation s’explique par un phénomène particulier de sédimentation, l’effet Boycott. Les propriétés statistiques de la suspension (densité, homogénéité) et des bulles (taille, forme, orientation) ont été caractérisées. On montre en particulier que l’on atteint un plateau pour l’aire de contact entre les trois phases (gaz/liquide/solide) en fonction du débit, indépendamment de la gravité effective – résultat important dans le cadre d’applications à des réactions catalytiques. Enfin, une large exploration de la gamme des paramètres montre, pour des cellules inclinées et certaines valeurs de débit de gaz, l’existence d’un régime oscillant : la taille du lit granulaire varie entre un état « creusé » (suspension très dense) et un état « comblé » (suspension peu concentrée). Une explication est proposée pour les temps de montée et de descente de ces oscillations. / We have studied experimentally particle suspension when injecting a gas at the bottom of an immersed granular layer, in confined geometry (Hele-Shaw cell). In a vertical setup, the system always reaches a stationary state resulting from the competition between grains entrainment by bubble rise, and sedimentation. A phenomenological model makes it possible to explain the properties of the suspension thus formed, and of the granular bed not affected by the gas rise. The influence of the effective gravity in the system is then considered. When a stationary state is reached, the size of the granular bed displays a maximum for a cell inclination angle of about 30-40 degrees. This observation can be explained by referring to a peculiar sedimentation process, the Boycott effect. Statistical properties of the suspension (density, homogeneity) and bubbles (size, shape, orientation) have been characterized. In particular, we show that the contact surface between the three phases (gas/liquid/solid) reaches a plateau when increasing the gas flow-rate, independent of the effective gravity. This result is important in the frame of possible applications to catalytic reactors. Finally, exploring a large range of parameters, we point out the existence of an oscillatory regime for inclined cells in a given range of gas flow-rates: the granular bed size oscillates between an "excavated" state (dense suspension) and a "filled" state: (dilute suspension). An explanation for the rising and falling time of these oscillations is proposed.

Nous avons étudié la dynamique de particules rigides et sphériques immergées dans un écoulement de cisaillement simple et oscillant à bas nombre de Reynolds. Les particules, au delà d’une déformation critique, se comportent de façon irréversible. La particules suivent alors un processus diffusif appelé: diffusion induite par cisaillement. Dans cette thèse, nous avons montré, par une approche numérique et expérimentale, que les collisions solides entre particules sont à l’origine de ce phénomène. Des simulations numériques ont été effectués afin d’évaluer l’importance relative des forces hydrodynamiques longues portées, des forces de lubrifications et des forces de contact. Deux expériences ont été effectuées afin de mettre en évidence l’influence des contacts solides entre particules. Nous avons étudié la dynamique de 3 particules soumises à un écoulement de cisaillement périodique. Les trajectoires des particules sont irréversibles durant le premier cycle et réversible pour les cycles suivants. En montrant que l’amplitude de l’irréversibilité est corrélée à la rugosité des particules, nous fournissons une preuve évidente que des collisions solides entre particules ont bien lieu et que ces collisions influencent la dynamique des particules. Effectuée dans une suspension homogène, le rôle des contacts a aussi été mis en évidence en montrant que l’amplitude critique de déformation dépend de la rugosité des particules. Un modèle géométrique simple qui considère des `particules effectives’ ayant un volume dépendant de l’amplitude de déformation et de la rugosité des particules, nous a permis de quantitativement reproduire les mesures expérimentales. / Even at low Reynolds number, particles within a shear flow exhibit irreversible dynamics. Many theories have been put forth to explain this phenomenon, the origin of irreversibility remains unclear. An integrated program of experimental and computational studies has been performed to assess the origin of the irreversible behavior of particles. Numerical simulations were used to evaluated the relative importance of long-range hydrodynamic interactions, lubrication, and contact forces. By isolating contribution of these interactions, we have shown that neither the long-range hydrodynamic interactions nor the lubrication are responsible for irreversibility. Solid contacts between particles largely dominate this phenomenon. However, producing realistic results requires both contact interactions and lubrication. Two different experiments were performed to address the role of contacts between particles in sheared suspensions. In the first experiment, the particle trajectories are irreversible during the first cycle but reversible for the next cycles. By showing that the magnitude of irreversibility increases with the particle roughness, we provide direct evidence that contacts occur in viscous flow. Experimental particle trajectories are well captured by the numerical model. In the second experiment, performed in a homogeneous suspension, the role of solid collisions was also revealed by showing that the critical strain amplitude depends on the particle roughness. A geometrical model based on the assumption that colliding particles produce irreversibility was derived. The model successfully reproduces the measured values of the critical strain amplitude.

Mechanical Integration of a Versatile Air Suspension into a Powered Wheelchair Joel Steinkraus It is undeniable that the vibration environment created by prolonged exposure to wheelchair use can cause discomfort for the rider and put him/her at risk of developing more severe medical conditions. While more research must be done to accurately quantify what constitues a harmful vibration environment, improved vibraiton isolation is an essential step. In order to incorporate structurally sound and effetive air suspension systems into motorized wheelchairs, a support structure is necessary. An after market wheelchair suspension system was designed, modeled, built and tested. Approximately 18 inches wide x 14 inches deep and 11 inches tall, the 50 lb suspension system uses a linear guide system and air spring to support the rider. A dashpot was added to prevent the amplification of the air spring’s natural frequency, and a pneumatic system installed to store and regulate the air pressure in the air spring and allow for a longer ride time. Testing of the system validates the mechanical durability of the design with respect to joint separation, plate bending, and bearing breakaway resistance. The penumatic system also is found to support up to 14 ingress/egress cycles before reaching a minimum functional pressure level. This value was achieved using an initial charge pressure of 100 PSI. Further environmental and user testing should be conducted to see if a greater number of ingress/egress cycles is necessary. Further development of the suspension system will incorporate a partially active controller for the air spring in order to to reduce the suspension’s transmisibility. Part respecificaitons are proposed in order to reduce system size and weight.

The conventional car suspension system uses isolated shock absorbers that are only capable of dissipating energy in the form of heat. Each shock absorber in a hydraulic interconnected suspension is connected by hydraulic circuits, allowing the electrified hydraulic fluid to be used to counteract undesirable body motion and enhance dynamic performance as a whole. An established idea with good potential for managing body rolling and separating the warp mode from other dynamic modes is the hydraulic interconnected suspension. While certain active or semi-active suspension technologies enable the shock absorbers to compensate for the effects of the road disturbances using external power input, hydraulic linked suspension is still passive and lacks adaptivity. In order to adjust the suspension's damping properties to rapidly changing road conditions, active suspensions, like electromagnetic shock absorbers, utilize the magnetofluid's variable viscosity. In some circumstances, the energy requirement of an active suspension might amount to kilowatts, which lowers the vehicle's fuel efficiency. This research proposes a novel energy-harvesting hydraulically interconnected shock absorber (EH-HISA) system to find a balanced solution to dynamic performance and energy efficiency by incorporating energy harvesting ability to a passive hydraulically interconnected suspension. Improved energy efficiency and vehicle dynamics performance are provided by the features which combine energy harvesting with hydraulic interconnection. AMESim is used to build a single diagonal hydraulic circuit model, which is then validated in a bench test. The theoretical model's validity was established by the bench test results, and the model was then applied to estimate system performance. To verify the effectiveness of the entire system design, a full car model outfitted with EH-HISA is created. For model simulation, various dynamic input scenarios—including sinusoidal input and double lane change tests—are applied. The EH-HISA achieves average lateral acceleration improvements of 38% over traditional suspensions and 11% compared to a prior design (EHHIS proposed by Chen et al.) and average energy harvesting ability improvements of 133 % while maintaining acceptable anti-rolling dynamics in the double lane change test. The EH-HISA also improves the anti-rolling ability by 30 % as compared to traditional suspensions. The power generated is found to reach maximum of 210 W at 2 Hz and 20 mm sinusoidal input. Bench tests are performed on the EH-HISA prototype to validate the simulation results. Damping force and energy harvesting experimental data is measured and compared with the simulation results to validate the effectiveness of the system. / Master of Science / The vehicle industry has always sought improved road handling dynamics and riding comfort. The vehicle body may move in a variety of ways, including roll, pitch, and bounce; each of these motions can endanger passengers' safety and lead to passenger fatigue. Oil shock absorbers that are isolated from the rest of the vehicle's suspension system can only dissipate energy by forcing oil via dampening valves. A hydraulic interconnected suspension can connect each shock absorber using hydraulic circuits so that the energized hydraulic fluid can be used to reduce unwanted body motion and enhance the overall riding experience. A tried-and-true idea, the hydraulic interconnected suspension (HIS), has shown promising results in stabilizing the vehicle body on unsteady roads. While active suspensions, like electro-magnetic shock absorbers, can employ an external power source to compel them to adjust to rapidly changing road conditions, hydraulic linked suspension is still passive and unadaptive. In some circumstances, the energy requirement of an active suspension might amount to kilowatts, which lowers the vehicle's fuel efficiency. Additionally, there is always a chance that a system that is actively receiving power will malfunction as a result of a power outage. This research offers a new type of energy-harvesting hydraulically interconnected shock absorber (EH-HISA) system to achieve a balanced solution to dynamic performance and energy efficiency. The combined energy-harvesting and HIS system provide improved energy efficiency as well as vehicle dynamics performance. Each system is composed of two distinct diagonal hydraulic circuits which interconnect the shock absorbers of the diagonal wheels in a vehicle. AMESim is used to build a single diagonal hydraulic circuit model, which is then validated in experiments, as a starting point for investigating the effectiveness of the overall system. The theoretical model's validity was established by the outcomes of the bench tests, and the model was then utilized to predict system performance. A full car model is created based on the tested single diagonal hydraulic circuit model to assess the performance of the entire system architecture. Different road condition scenarios are used for model simulation, which includes sinusoidal input and double lane change test. The EH-HISA achieves average lateral acceleration improvements of 38% over traditional suspensions and 11% compared to a prior design (EHHIS proposed by Chen et al.) and average energy harvesting ability improvements of 133 % while maintaining acceptable anti-rolling dynamics in the double lane change test. The EH-HISA also improves the anti-rolling ability by 30 % as compared to traditional suspensions. The power generated is found to reach maximum of 210 W at 2 Hz and 20 mm sinusoidal input. Bench tests are performed on the EH-HISA prototype to validate the simulation results. Damping force and energy harvesting experimental data is measured and compared with the simulation results to validate the effectiveness of the system.

No description available.

Future railway trends require travelling at high speeds without deterioration in the ride quality, but further improvement of the ride quality by optimisation of the passive suspension components has reached its limits. This suggests that active suspensions should be used. Rigorous studies over the past four decades have shown that this technique is able to overcome the passive suspension limitation in terms of improving the overall ride performance of the railway vehicle with the incorporation of additional active elements i.e. actuators, sensors and processors. The work in this thesis investigates a novel method for controlling the actuators within the suspension system, something which has been neglected in previous studies. It is a particular problem because at higher frequencies, when the suspension is providing isolation of the car body from the track irregularities, the actuator must accommodate the suspension movements whilst producing very small forces, otherwise the ride quality substantially deteriorates. Instead of considering more complex active suspension control strategies, which tend to be complex and may be impractical, the performance of the actuator across the secondary suspension is investigated. This research looks into improving actuator technologies for railway secondary suspensions in order to achieve the full benefits of active control. This thesis explores novel methods to improve the ride quality of the railway vehicle through secondary suspension actuator and controller design, with the ultimate aim of integrating this technology into a fully active railway vehicle. The focus of this active suspension research is therefore upon incorporating real actuator technology, instead of the usual assumption of ideal actuators. For meaningful and reliable research a simple, well established active control strategy is used for assessment to highlight the degradation in the suspension performance compared with the ideal actuators. Preliminary investigation demonstrates significant degradation of the ride quality caused by real actuators in the secondary suspension, and this research looks at methods to reduce this effect. Including actuators within a secondary suspension system is a difficult actuator problem compared to the normal application of actuators such as position control. This is because the actuator controller design process requires the consideration of the interaction of the vehicle suspension. The actuators that have been identified as suitable for the application are the electromechanical and servo-hydraulic types, and these are incorporated across the secondary suspension. The effects of the actuator dynamics have been analysed. Practical classical controllers are used to provide force-feedback control of both types of actuator in the secondary suspension. A variety of actuator control techniques are considered including: optimisation of the actuator controller parameters to solve the multi-objective and multivariable problem, the introduction of feed forward techniques and the use of optimal control approaches.