A heat pipe is a heat transfer device of very high thermal conductance that features two-phase flow. Research at McGill University has led to the development of the McGill Heat Pipe which includes an internal flow modifier. Such a heat pipe can be operated at very high heat fluxes. This area of heat pipe technology has potential in many applications in metallurgical industries. / This thesis describes how the McGill heat pipe was developed, tested, modeled and applied in high heat flux situations. Until the development of the McGill Heat Pipe, three main issues had prevented the successful use of heat pipe technology in high heat flux applications. These relate to limitations imposed by film boiling, dry-out, and the structure of the flow. The McGill Heat Pipe has successfully addressed and overcome these limitations. / To overcome film boiling and dry-out, a flow modifier was developed. The structure of the flow was changed by introducing a reservoir and a return line. This thesis describes some of the work that is being carried out to develop and evaluate families of flow modifiers, or spiral springs. Results from a number of high flux experiments will be detailed and the effects of the flow modifiers for each case will be described. In addition, the velocity of the return water was visualized with magnesium alloy chips and was measured with a video camera. Comparisons of the operation of the heat pipe both with and without a flow modifier are presented. This is the first study of its kind in which a transparent glass return line and particles were used to visualize the liquid flow in the return line of the heat pipe.

We present a novel model describing the nucleation and the initial growth of bundles of carbon single-walled nanotubes (C-SWNTs). The formation of the catalyst nanoparticle, on which bundles of C-SWNTs grow, is first investigated. A qualitative analysis of the carbon-catalyst phase diagram shows that the gas-phase synthesis process leads to the formation of a nanometric liquid layer, supersaturated in carbon, surrounding the catalyst nanoparticle. It is then claimed that a solutal Benard-Marangoni instability governs the flow of carbon in the liquid layer. Using results from linear stability analyses, it is shown, for a planar and a spherical geometry, that the onset of the solutal Benard-Marangoni instability in the liquid layer is possible and favoured with respect to other fluid instabilities. Subsequently, results from a weakly nonlinear stability analysis (in a planar geometry) and from a bifurcation analysis (in a spherical geometry), are leveraged in order to show that the instability leads to the formation of hexagonal convection cells. It is argued that, once initiated, the solutal Benard-Marangoni instability provides the kinetic mechanism necessary for the nucleation and the initial growth of bundles of C-SWNTs. This model provides an explanation for aspects of the growth still unclear, such as the nucleation mechanism, the nanometric diameter of C-SWNTs and their collective organization into bundles, at the onset of the growth.

This dissertation studies three aspects of airfoil flows: (i) second-order theoretical solutions of airfoils in steady flows; (ii) unsteady solutions for oscillating flexible airfoils; and (iii) numerical analysis of airfoil flows at low Reynolds numbers. / The first part presents simple and efficient analytical solutions in closed form for the velocity and pressure distributions on airfoils of arbitrary shapes in steady flows, which are obtained using special singularities in the expression of the fluid velocity. A second-order accurate method is first developed for airfoils in inviscid incompressible flows to simultaneously solve the symmetric and anti-symmetric flow components defined by coupled boundary conditions. Then, the method is extended to take into account the viscous and compressibility effects on the pressure distribution. The resulting solutions were found to be in very good agreement with the available exact solutions (for specific airfoils), and with numerical and experimental results at various Mach and Reynolds numbers and moderate angles of attack. / The second part presents a new method of solution for the analysis of unsteady incompressible flows past oscillating rigid and flexible airfoils. The method has been successfully validated by comparison with the results obtained by Theodorsen and by Postel and Leppert for rigid airfoil and aileron oscillations in translation and rotation. The aerodynamic stiffness, damping and virtual mass contributions are specifically determined, as required in the aeroelastic studies. In all cases studied, this method led to very efficient and simple analytical solutions in closed form. / The third part presents an efficient numerical method for the incompressible flows past airfoils at low Reynolds numbers, which are of interest for micro-aircraft applications. The present analysis is based on a pseudo-time integration method using artificial compressibility to accurately solve the Navier-Stokes equations. Solutions are obtained with this method for airfoils at various incidences and very low Reynolds numbers between 400 and 6000. A detailed analysis is presented for the influence of the Reynolds number, incidence and airfoil shape on the pressure distribution, lift and drag coefficients. The flow separation is especially studied; the separation and reattachment positions are compared for various airfoil shapes, incidences and Reynolds numbers.

Task uncertainty and noise---generically referred to as uncertainties in the thesis---in the design and operation of robotic mechanical systems pose a major challenge to the designer. The aim of this thesis is to contribute to the laying down of the foundations on which the design of robotic mechanical systems, in the presence of uncertainties, is to be based. Uncertainties are accounted for by means of robustness. To this end, a theoretical framework as well as a general methodology for model-based robust design are proposed. Within this framework, all quantities involved in a design task are classified into three sets: the design variables (DV), which are to be assigned values as an outcome of the design task; the design-environment parameters (DEP), over which the designer has no control; and the performance functions (PF), representing the functional relations among performance, DV and DEP. A distinction is made between globally robust design and locally robust design, this thesis focusing on the latter. Locally robust design is amenable to mathematical modelling of the performance by means of smooth functions of the DV and DEP. Resorting to the mathematical model available for the object under design, a design performance matrix, mapping the space of relative variations in DEP---referred to as noise in the literature on robust design---into that of relative variations in PF, is derived. Then, the locally robust design problem is formulated as the minimization of a norm of the covariance matrix of the variations in the PF upon variations in the DEP. Moreover, one pertinent concept are introduced: design isotropy. Next, it is shown that an optimally robust design can be secured by means of isotropy, whenever this is achievable under the constraints of the problem at hand. As proven in the thesis, designs obtained via isotropy lead to robustness even in the absence of a priori knowledge of the statistical properties of the variations of / In connection with robotic mechanical systems, the design task is decomposed into three subtasks, namely, kinetostatic, elastostatic, and elastodynamic, in this order. We show that parallel manipulators allow for isotropic designs, but their serial counterparts do not. / The motivation behind the research work reported here being the design of robotic mechanical systems, the simulation of their dynamic response becomes an essential component in their design. In order to validate the proposed design, a robust algorithm for the simulation of conservative linear systems, which model accurately the systems of interest in the presence of "small" environment perturbations, is introduced. The robustness of the algorithm lies in its immunity to roundoff and truncation errors, which could lead to either instability or a dissipative response in the simulation results otherwise.

In order to elucidate the effect of chemical kinetics on the dynamic structure of a detonation, an investigation is carried out by means of high-resolution numerical simulations of the reactive Euler equations. The chemical description ranges, with increasing complexity, from simplified single-step reaction kinetics to complex models with detailed chemical reaction rates. / To illustrate the unsteady dynamics of the detonation structure and its dependence on chemical kinetics, a one-dimensional pulsating detonation with one-step kinetics has been investigated. Different nonlinear dynamics of the pulsating front are observed by varying the global temperature sensitivity of the chemical process. Numerical results have suggested that the route to higher oscillation modes may follow closely the Feigenbaum scenario of a period-doubling cascade leading to the existence of chaos as observed in many generic nonlinear systems. The remarkable similarity between a simple nonlinear dynamical system and the pulsating detonation structure suggests that the use of a nonlinear oscillator model can be considered to explore the role of chemical kinetics on the instability spectrum of the oscillatory front. / To clarify the importance of chain-branching reactions and to resolve the drawbacks associated with the single-step Arrhenius model, a thorough analysis of the pulsating detonation using a two-step reaction mechanism, consisting of a thermally neutral induction step followed by a main reaction layer, has been carried out. It is found that the dynamics of detonation structure depend not only on the temperature sensitivity of the reaction but also the shape of the reaction zone characterized by the length of induction and main heat release layer. From the parametric study, a relevant non-dimensional stability parameter chi and its associated neutral stability curve have been determined. These results are further generalized to more complicated kinetic models of detonation in real gaseous mixtures. They provide a tool to elucidate different experimental observations on the detonation structure such as the cell regularity, the effect of argon dilution and the propagation mechanism. An improved model for the prediction of the characteristic cell size of a detonation is also formulated by including the present stability parameter chi. / To deduce a global method to examine the transient reaction structure of the detonation, the head-on collision problem of a detonation with a shock wave has been proposed. The present study concerned with the effect of chemical kinetics on the unsteady dynamics of the head-on collision phenomenon. Numerical simulations have demonstrated that the unsteady interaction involves a relaxation process consisting of a quasi-steady period and an overshoot for the transmitted detonation subsequent to the frontal collision, followed by the asymptotic decay to a CJ detonation. Due to the change of chemical kinetics as a result of the increase in the thermodynamic state of the reactive mixture froth shock compression, the transmitted pulsating detonation can be stabilized with smaller amplitude and period oscillation. These observations are in agreement with experimental evidence obtained from smoked foils where significant decrease in detonation cell size after a region of relaxation is observed when the detonation collides head-on with a shock wave.

Manipulators, working in space, execute a wide range of tasks, such as loading or un- loading, servicing, and assembly operations. Motion of the manipulator, mounted on a free-flying satellite, creates the reaction forces and moments, which, transmitted to the base, alter its position and orientation. The Reaction Null-Space (RNS) manipula- tor path planning algorithm, which ensures reactionless manipulator motion, has been chosen to develop a trajectory for a planar satellite-mounted three-link manipulator intercepting a target. Three cases of manipulator motion, subject to different con- straints, have been studied: (1) constraints on the joint acceleration and reaction force norms at the point of interception, (2) constraints on joint accelerations at the inter- ception point, and (3) minimum joint acceleration along the whole trajectory. Three reactionless path planning algorithms corresponding to the above constraint scenarios have been implemented in MatLab. The absence of base rotational disturbances has been verified by simulating the base-manipulator system with the reactionless joint motions using MSC Adams software. / Les manipulateurs, mobiles dans l'espace, r ́ealisent une large gamme de taˆches telles que le chargement ou d ́echargement, l'assemblage ou encore les services. Le mou- vement d'un manipulateur mont ́e sur un satellite cr ́e ́e une force et un moment de r ́eactions qui, transmis `a la base du satellite, en modifient la position et l'orientation. Assurant un mouvement du bras sans r ́eaction sur la base, l'algorithme de trajectoire du manipulateur Reaction Null-Space (RNS) a ́et ́e choisi pour d ́eterminer la trajec- toire d'un manipulateur tri-segment plan mont ́e sur satellite et destin ́e `a l'interception d'objets. Trois cas de mouvements, soumis `a diff ́erentes contraintes, ont ́et ́e ́etudi ́es: (1) contraintes sur les normes de l'acc ́el ́eration de l'articulation et de la force de r ́eaction au point d'interception, (2) contraintes sur l'acc ́el ́eration de l'articulation au point d'interception, et (3) minimum de l'acc ́el ́eration moyenne de l'articulation tout au long de la trajectoire. Trois algorithmes de mouvement sans r ́eaction correspon- dants aux trois cas pr ́ecit ́es ont ́et ́e cod ́es sous MatLab. L'absence de perturbation de l'orientation de la base a ́et ́e v ́erifi ́ee en simulant, `a l'aide du logiciel MSC Adams, le syst ́eme compos ́e de la base et du bras lors d'un mouvement de l'articulation.

The structure of a wheel intended for lunar applications requires an innovative design because of the Moon's specific environment. As in-situ prototype testing is obviously unfeasible, testing can only be conducted on lunar simulant soils, or through simulations. This study presents wheel-soil interaction simulations using the discrete element method (DEM) software EDEM and their use for tread shape optimization. The DEM parameters of EDEM's contact-model are first reviewed before presenting a systematic methodology of their calibration. The first step consists in measuring key properties of the real soil with basic experiments and simulating these experiments for different values of the virtual soil's design variables. The soil's response surfaces of the targeted properties are then computed, and an optimization algorithm is developed to determine the optimum sets of design variables that minimize the discrepancy of the properties between the real soil and the virtual one.Then, two different approaches of three-dimensional wheel-soil simulations are described. The first approach involves a displacement-controlled wheel, its tractive performance being measured for various grouser configurations. In the second approach, the wheel is torque-controlled and performances, such as power consumption or speed, are investigated and validated experimentally.This work proposes a soil simulation and shape optimization tool for the design of a rigid wheel tread that targets a need of the Canadian aerospace industry. / La structure d'une roue destinée à une application lunaire doit être le fruit d'une conception innovante afin de s'adapter à l'environnement très particulier de la surface de la Lune. Comme les prototypes ne peuvent être testés sur site, des tests sont possibles uniquement sur Terre, sur des simulants de sol lunaire ou en simulations. Dans cette étude, des simulations d'interactions roue-sol utilisant la méthode des éléments distincts (MED) et le logiciel EDEM sont présentées, ainsi que leur utilité dans le cadre de l'optimisation de la géométrie de la bande de roulement.Tout d'abord, les paramètres MED intervenants dans le modèle de contact de EDEM sont passés en revue et une méthodologie systématique pour leur calibration est proposée. La première étape de cette méthodologie consiste à mesurer des propriétés importantes du sol à modéliser à l'aide d'expériences simples, puis de simuler ces expériences en variant les valeurs des paramètres MED. Les surfaces de réponse pour les propriétés ciblées sont ensuite calculées, et un algorithme d'optimisation détermine les valeurs optimales des paramètres afin de minimiser les différences entre les propriétés du sol réel et celles du sol virtuel.Ensuite, deux approches de simulations roue-sol tridimensionnelles sont décrites. La première approche implique une roue asservie en déplacements. Les performances en traction de la roue sont mesurées pour différentes configurations de la bande de roulement. Dans la deuxième approche, la roue est contrôlée par un couple moteur, et d'autres performances telles que la puissance consommée ou la vitesse peuvent ainsi être mesurées et validées expérimentalemnt.Enfin, les possibilités des simulations proposées en terme d'optimisation de la structure de la bande de roulement de roues rigides sont exposées.

Huge amounts of energy expended on comminution devices, such as ball mill, besides being a highly inefficient process has been the motive of much research aiming at improving the efficiency of comminution processes. Comminution theories are mainly based on size distribution of the ore and consequently fall short in addressing other imperative phenomena, such as media wear and more importantly energy utilization efficiency. A methodology based on an energy viewpoint is proposed for comminution studies which can serve as a powerful tool in design and performance optimization of comminution devices. Through this approach, the relation between operating parameters and optimization objectives which are the reduction of media wear and increase in ore breakage and energy efficiency could be explored. On the other hand, since field testing of comminution models is expensive, standard laboratory test methods which could reliably simulate the comminution conditions similar to the actual application environment are needed. While there are standard test methods for wear or breakage characterization of the materials individually, there is a need for standard test methods which enable us to conduct combined study of wear and breakage to create an environment similar to the actual applications. The Steel Wheel Abrasion Test is one of the candidates which provide us with such environment to study wear, breakage and their interrelation in one apparatus because of its high-stress nature of abrasion. Furthermore, more precise tools of describing the quantity and quality of the breakage and abrasive wear are introduced. Experimental results extracted from steel wheel abrasion test are analyzed using proposed methodologies and energy-based approach. / La faible efficacité du processus de comminution et son énorme coût énergétique ont été les raisons de nombreuses études visant à améliorer l'efficacité des processus de broyage. Les théories de la comminution sont principalement basées sur la distribution granulométrique du minerai et par conséquent ne parviennent pas à aborder d'autres phénomènes impératifs comme l'usure d'agents ou l'efficacité d'utilisation de l'énergie. Une méthodologie basée sur un point de vue énergétique est proposée pour les études de comminution, et peut servir comme outil puissant dans la conception et l'optimisation de la performance des dispositifs de comminution. Grâce à cette approche, la relation entre les paramètres de fonctionnement et les objectifs d'optimisation, qui sont de minimiser la quantité et la gravité de l'usure et d'augmenter la fragmentation du minerai et l'efficacité énergétique, pourrait être explorée. De plus, l'essai pratique des modèles de comminution est coûteux et des méthodes standards de test en laboratoire pouvant simuler de manière fiable la comminution dans des conditions similaires à l'application réelle sont nécessaires. Bien qu'il existe des expériences standardisées pour la caractérisation d'usure ou la fragmentation des matériaux individuellement, il y a un besoin de méthodes d'essai normalisées pour procéder à l'étude combinée de l'usure et de la fragmentation dans un environnement semblable à celui des applications réelles. Le test d'abrasion par roue d'acier est l'un des candidats qui peut nous fournir un tel environnement pour étudier l'usure abrasive, la fragmentation et leur interrelation dans un seul appareil. En outre, des outils plus précis pour décrire la quantité et la qualité de la fragmentation et l'usure d'abrasion sont introduits. Les résultats expérimentaux extraits de test d'abrasion par roue d'acier sont analysés en utilisant des méthodes proposées et une approche fondée sur l'énergie.

Complementary computational and experimental investigations of steady, laminar, mixed convection in a heated vertical pipe, with slurries of a microencapsulated phase-change material (MCPCM) suspended in distilled water as the working fluid, are presented in this thesis. / The MCPCM consists of particles composed of a core of phase-change material (PCM) surrounded by a solid shell: The effective diameter of the particles is 2.5 mum; the melting and freezing temperatures of the PCM in the particles are in the ranges 27°C to 31°C (mean value 29.94°C) and 12°C to 16°C (mean value of 14.64°C), respectively; the latent heat of fusion during melting is 131.8 kJ/kg. Experimental apparatus and procedures for measurements of the effective density, the effective viscosity, the effective thermal conductivity, and the effective specific heat of the MCPCM slurries are presented along with results and correlations that apply to temperatures in the range 5ºC to 60ºC. / In the presentation of the computational investigation, a homogenous mathematical model is shown to be applicable and proposed; procedures for incorporation of correlations for the effective properties of the MCPCM slurries are discussed; difficulties with the standard definition of bulk temperature when the specific heat of the fluid changes significantly with temperature are elaborated; a modified bulk temperature that overcomes these difficulties is proposed; a finite volume method is described; and its validation and use in the computer simulations are discussed. / An apparatus that was designed, constructed, benchmarked, and used in the mixed-convection experiments is described. Details of this experimental investigation, conducted with slurries of mass concentration 0% (pure distilled water), 5%, 10%, 15%, and 20%, temperatures in the range 20°C to 60°C, and volume flow rates in the range 1.78 mL/s to 2.69 mL/s, are presented. / The experimental and numerical results are presented, compared, and discussed. They show that the proposed homogenous model, with input of correlations that give the variation of the effective properties of the MCPCM slurries with temperature, provides a cost-effective and accurate foundation for computer simulations of the problems of interest.

As a contribution towards understanding, modeling and controlling the combustion of oxygenated hydrocarbons such as biofuels, the high-temperature ignition of a series of relevant molecules has been investigated behind reflected shock waves at pressures ranging from 1 atm to 13 atm. Short chain biodiesel surrogates, methyl and ethyl esters, have been investigated. Methyl esters of formic to butanoic acids have been investigated in order to uncover the trends in their ignition delay times. The trends have further been explored by means of computational quantum chemical calculations. While most of these surrogates portray similar ignition behavior, the influence of structure with respect to terminal methyl groups and the presence or absence of secondary C–H bonds have been observed as in the case of methyl acetate with longer ignition delay times. The role of the alkyl group on the ester reactivity has been investigated by comparing methyl and ethyl esters, with the result that ethyl esters are generally more reactive. Apart from these biodiesel surrogates, selected C3 oxygenates, relevant to combustion have been investigated. A chemical kinetic mechanism for the high-temperature oxidation of propanal is developed and tested. Propanal, like other aldehydes, belongs to the group of intermediate species which occur in the combustion of almost all hydrocarbons, but their accurate prediction in combustion modeling is challenging. Targeted studies of the submodels of these compounds are expected to contribute towards predictive chemical kinetic modeling. The developed mechanism also shows encouraging performance in the prediction of acetaldehyde (ethanal) ignition. Ethanol is another biofuel widely used in spark-ignition engines. There is also interest in using this fuel in diesel and Homogeneous Charge Compression Ignition (HCCI) engine concepts. This is in line with the need for tailor-made, flexible fuels for wide range applications in energy conversion. Ethanol ignition modification by isopropyl nitrate (IPN), isopropyl formate (IPF) and water has been investigated. It is found that whereas IPN improves the ignition performance of ethanol (shorter ignition delay times), IPF increases its ignition resistance (longer ignition delay times), so that it can be used as an anti-knock agent. It is further observed that at temperatures above 1400 K, IPN addition ceases to improve the ignition of ethanol. Wet ethanol ignition reveals that at the same post-shock temperature water has an ignition promoting effect. The feasibility of igniting wet ethanol raises the prospect of reducing ethanol production cost (distillation) by using ethanol with allowable water content, albeit with a lower specific energy content. The ignition behavior of the biodiesel surrogate, methyl butanoate, and the diesel surrogate, n-heptane, is compared. Similar behavior is observed under stoichiometric conditions, with slight differences under rich conditions. A skeletal mechanism is proposed for the combustion of blends of the two surrogates. The skeletal mechanism is derived from reduced skeletal mechanisms of literature mechanisms for n-heptane and methyl butanoate obtained on the basis of extensive ignition sensitivity analyses and chemical kinetic insight. These reduced skeletal models have been found to perform reasonably well when compared to predictions by their original detailed mechanisms with respect to ignition, flame propagation and the structure of an opposed flow flame in the mixture fraction space. A systematic approach has been taken in this work to compare the reactivity of fuels, which leads to insight on trends, similarities and differences in global ignition behavior. The combination of experiments, analyses, computations and modeling demonstrates the synergy required to address problems in modern combustion science and technology. / En tant que contribution à la compréhension, la modélisation et le contrôle de la combustion des hydrocarbures oxygénés tels que les biocarburants, l'auto-allumage à haute température d'une série de molécules a été étudiée avec la méthode de tube a onde de choc pour les pressions entre 1 atm et 13 atm. Les molécules représentatives du biodiésel, c'est à dire des esters méthyliques et éthyliques, ont été étudiées. Les esters méthyliques d'acide formique jusqu'à butanoique ont été étudiés afin de découvrir l'influence de leurs structures sur l'auto-allumage. Cette relation a aussi été examinée avec les calculs de la chimique quantique. Alors que la pluparts de ces esters sont marqués par des délais d'auto-allumage similaires, les influences des groupes méthyliques terminales, et la présence ou absence des liaisons secondaires de C-H, ont été identifiées, comme dans le cas d'acétate de méthyle, caractérisé par les plus longs délais. Le rôle du groupe alkyle sur la réactivité d'ester a été étudié en comparant des esters méthyliques avec les esters éthyliques. Les esters éthyliques sont généralement plus réactifs que les esters méthyliques du même acide. De la même manière, sont investigués quelques hydrocarbures oxygénés, dont leur cinétique d'oxydation est impliquée dans la combustion des biocarburants et carburants pétrolifères. Un mécanisme de la cinétique chimique pour la combustion du propanal à haute température a été développé et validé. Le propanal, comme d'autres aldéhydes, appartient au groupe des espèces intermédiaires qui se forment pendant la combustion de presque tous les hydrocarbures, mais leur modélisation reste imprécise. Des études consacrées à la compréhension des sous-modèles de ces molécules devraient contribuer à la modélisation avancée de la cinétique chimique de la combustion. Le mécanisme proposé prédit aussi les délais d'auto-allumage d'acétaldéhyde, dont le sous-mécanisme est inclus. L'éthanol est un biocarburant largement utilisé dans les moteurs à allumage commandé. Il y a également intérêt à utiliser ce carburant dans les moteurs à allumage par compression. Ceci est en accord avec la nécessité de développer des carburants flexibles pour des moteurs divers. La modification de l'auto-allumage de l'éthanol par des additifs chimiques comme le nitrate d'isopropyle (IPN), le formiate d'isopropyle (IPF) et l'eau a été investiguée. Il se trouve que, alors que l'IPN améliore la tendance à l'auto-allumage de l'éthanol (délais plus courts), l'IPF augmente sa résistance à l'autoallumage, de sorte que ce dernier peut être utilisé comme additif pour supprimer l'autoallumage. Pour une même température, l'auto-allumage de l'éthanol contenant de l'eau se révèle accélérée. Un mécanisme pour la combustion des mélanges de diesel et du biodiesel est également proposé. Le mécanisme est dérivé de la réduction des mécanismes détaillés pour le n-heptane et le butanoate de méthyle obtenus sur la base de l'analyse de sensitivité de l'auto-allumage. Cette méthode comparative systématique et innovatrice cherche à caractériser les propriétés des carburants oxygénés en vue de révéler les similitudes et les différences. Les résultats servent à l'optimisation des modèles cinétiques chimiques ainsi qu'à la compréhension de la cinétique de combustion d'une série d'espèces oxygénées. Des corrélations de délais d'auto-allumage sont également proposées pour l'application pratique. Le mécanisme proposé pour les mélanges diesel et biodiesel se prête à l'étude de la combustion dans les écoulements turbulents.