A numerical investigation was conducted to analyze the unsteady flow and heat transfer characteristics for cylinders of square cross-section in a laminar channel flow The study focuses on differences in the drag, lift, and heat transfer coefficients for a single and tandem pair of cylinders due to the proximity to a channel wall. Both uniform and parabolic inlet velocity profiles are considered. The cases are calculated for a fixed cylinder Reynolds number of 500 and a Prandtl number of 0.7. The heated cylinder is held at a constant temperature and is initially centered in the channel. The eddy promoter has side dimensions one-half of the downstream cylinder and is placed at a fixed distance upstream. The upstream cylinder is either located midway between the top and bottom cylinder surfaces (inline) or it is centered on the top or bottom edges (offset) of the primary cylinder. The results show that the cylinder Nusselt number decreases for both single and inline tandem cylinders as they approach the wall in a parabolic flow but remain almost constant in a uniform flow. This is primarily due to the reduced mean velocity near the wall. The time-averaged drag coefficient decreases for both single and inline tandem cylinders as they approach the wall in a parabolic flow. The presence of the upstream cylinder significantly reduces the drag on the downstream cylinder when compared to that of a single cylinder but has little affect on the cylinder lift. Additionally, the overall cylinder Nusselt number increases slightly in both uniform and parabolic flows. The Strouhal number is much larger for an inline tandem pair than for a single cylinder for all cylinder positions. The amplitude of eddy-shedding induced oscillations is significantly dampened as the cylinder(s) approach the channel wall. Offsetting the eddy promoter causes a significant reduction in the heat transfer and a large increase in the drag coefficient for the channel-centered cylinder when compared to the inline tandem case. The offset cylinder is found to slightly reduce the overall heat transfer and increase the drag from the downstream heated cylinder for the other two cross-stream locations. The study also indicates that placing the eddy promoter in higher velocity fluid increases the Strouhal number of the downstream cylinder.

Random vibration coupled with thermal cycling is a common environment for a lot of mechanical and electrical products, especially for those experiencing transportation and handling frequently. Today, random vibration plus thermal cycling have been broadly applied as an important stimulus stress to expose the latent defects during development. In addition, drop tests are also necessary for these products since an accidental drop may seriously damage them. Both random vibration and drop tests are expensive. Plate element is popular in portable and transportation related products, for example, the Printed Circuit Boards (PCBs) in equipment installed in vehicles, the Liquid Crystal Displays (LCDs) in portable computers and the skin panels near the engines in airplanes. These plate elements are subjected to random vibration and thermal cycling, and some of them may encounter a drop. Even through the deterministic vibration theory of plates has been developed a lot, the random vibration theory of plates has not been well explored yet, particularly in reliability quantification, response analysis, and thermal load effect. In this dissertation, a random vibration analysis model for packaged plates is proposed for base excited random vibration coupled with temperature loads. Based on this model, a reliability quantification model is proposed, too. Two common random vibration power spectral densities "Ideal White Noise (IWN)" and "Band Limited White Noise (BLWN)" are researched. As a result, the closed form solution for IWN is derived and the numerical procedure for BLWN is presented. By comparing the IWN results with the BLWN results, an application limit to IWN is discovered. The effects of temperature and damping on reliability are then investigated. For the drop load case, the response process and the reliability are researched, and the illustrative example is given to demonstrate the methodology. The research results of the dissertation may supply designers with guidelines and supplement testing with analytical data; therefore, the test cost can hopefully be cut down. The methodologies can be applied to the evaluation of transportation reliability.

The atmosphere of Mars is a potential source of the gases essential for human exploration missions. Many international space agencies and scientists have shown great interest in developing chemical plants to make propellants and life-support consumables utilizing the red planet's atmosphere and Earth-sourced H₂. Electrolyzing carbon dioxide to produce oxygen by a solid oxide electrolysis cell has been proven to be a potential candidate. A solid oxide electrolysis cell, which consists of 8mol% yttria-stabilized zirconia sandwiched between two electrodes, is designed, manufactured and tested. The electrode/electrolyte interfacial polarization characteristics are investigated with the aid of the current interruption method using a four-electrode set-up. Activation overpotentials, which are free of ohmic losses, are measured in the temperature range from 1023 to 1123K for the carbon dioxide electrode and the oxygen electrode. Both the electrode activation overpotentials show the Tafel behavior. In order to increase the active electrochemical reaction sites, platinum yttria-stabilized zirconia cermet electrode is investigated. A solid oxide electrolysis cell with cermet electrodes shows high performance and significantly reduces anode activation overpotentials, and ohmic resistance as well. A 1-D steady state solid oxide electrolysis cell model is set up to take into account different kinetics: (1) surface exchange kinetics at the gas/electrode interface involving adsorption/desorption; (2) mass transfer of the reactants and products involving the bulk diffusion and surface diffusion; and (3) electrochemical kinetics involving charge transfer at the triple phase boundary. The solid oxide electrolysis cell's performance and voltage are predicted at any given current based on this model. The effects of surface diffusion coefficients, adsorption/desorption rate constants, and anodic/cathodic reaction rate constants on carbon dioxide electrolysis are studied. A comparison of solid oxide electrolysis cells between the numerical results and the experimental results is made.

In this dissertation a characteristic equation has been obtained, in the framework of the linear theory of elasticity, for multilayered pipes; individual layers are made of isotropic elastic solids. A theoretical study of the Lamb wave propagation in multilayered pipes for both axisymmetric and nonaxisymmetric loading is presented. The stress and displacement variations inside the multilayered pipe are theoretically calculated for a number of propagating Lamb modes. The Lamb wave dispersion curves and the curves of frequency versus the ratio of wall thickness to half wave length have been computed for different Lamb modes inside a homogeneous pipe and have been compared with published results. These computations are extended to multilayered pipes.

A condition for the onset of shear localization for the two-dimensional plane strain case is presented. Based on the condition, shear localization in three different problems are studied. By using the NIKE2D finite element package, a punching process for thin sheet metal with frictional surfaces is analyzed and the relationship between the frictions and shear localization is discussed.

In the present work, the quenching of gaseous hydrocarbon-air flames in packed beds of spherical particles has been investigated experimentally. Experiments were carried out in the standard flammability apparatus of Coward and Jones modified by the insertion of a packed bed of solid monosize spheres in the flame tube. Laminar flames were spark-initiated in quiescent combustible mixtures and failure or successful transmission of the flames through the packed bed was determined by visual observation. The quenching limits were determined as a function of the packed bed parameters (i.e., sphere material, sphere size, length of packed bed, etc.) to elucidate the mechanisms of flame extinction in the bed of spherical particles. The results have direct application to the design of flame arrestors using a packed bed as the flame arresting element. / The flame quenching limits are found to be relatively insensitive to the material of the solid spheres, but are dependent on the sphere size through a characteristic length scale that describes the open passages of the packed bed. Flame extinction was always observed to occur within a few millimeters of penetration into the packed bed section indicating that the length of the packed bed has little influence on the quenching of laminar flames. Analysis of the experimental results indicates that the mechanism for flame quenching in a packed bed is governed primarily by heat loss to the sphere surfaces by conduction, convection effects being negligible in the small channels of the packed bed. It is shown that, while conduction is the dominant flame quenching mechanism, selective diffusion and flame stretch also play an important role in the quenching process.

Parallel mechanisms are being introduced as platforms for machine tools, where stiffness and vibration supression is vital. A novel parallel architecture, called double triangular (DeltaDelta), was proposed and studied in depth by Daniali in anticipation of applications which require fast and precise motion. However, Daniali failed to find the minimal solution to the spherical DeltaDelta parallel manipulator, which he suspected is quadratic. Here, projective geometry and Grassmannian incidence relationships are used to unify the method of direct kinematic analysis (DKP) of two types of three degree-of-freedom manipulators, viz., the planar and spherical versions of DeltaDeltaPM, while preserving the geometric meaning of the solution. This method was to demonstrate for the first time that SDeltaDeltaPM can have only two real assembly modes; however, the minimum solution is found to be of order eight. An example is included to show that SDeltaDeltaPM can actually possess eight real assembly modes. Only two of the eight real poses lie within the workspace, while the other six arise due to a quadruple triangular tesselation of the sphere. Furthermore, a method to solve the general three-points-on-three-lines problem along with application to statics and spatial parallel manipulators is presented.

This thesis contains measurements of the wall pressure fluctuations on cylinders in a bundle in turbulent axial flow in a cylindrical channel. The measurements were made for the purposes of obtaining insight into the nature of the turbulent pressure field and providing analytical approximations of wall pressure correlations required by a previously derived theory for predicting the flow-induced vibration of cylinders in axial flow. / The turbulent pressure field at the walls of the cylinders is examined in both the frequency and time domains via measured power-spectral densities, cross-spectral densities, auto-correlations and cross-correlations in azimuthal and longitudinal planes in the cylinder bundle over a range of flow velocities. The data is then nondimensionalized to give dimensionless power-spectral densities and azimuthal (or lateral) and longitudinal correlation functions, which are then approximated analytically and compared to a previous analytical approximation for pipe flow. Typical force-per-unit-length spectra are also obtained from the pressure measurements.

TRansformation Induced Plasticity (TRIP) is an important phenomenon during which metastable retained austenite transforms to martensite as a result of imposed stress or strain. This phenomenon was highlighted in fully austenitic stainless steels during the 1970s and thoroughly studied for two decades to understand its complexity. More recently the same strengthening phenomenon has been used in low alloy TRIP assisted multiphase steels resulting in a simultaneous increase in strength and ductility. The full potential of this class of steels is yet to be uncovered due to the complexity of the TRIP transformation and its dependence on various physical conditions and their interactions. In this work, the metallurgical and mechanical properties of four TRIP assisted multiphase steels are characterised under physical conditions emulating those faced during automotive crash. This is done by studying the effects of the strain, strain rate, stress state and temperature on the transformation kinetics and mechanical properties of these steels. A phenomenological constitutive model for predicting the quasi-static and high strain rate mechanical response of these steels is proposed. The model incorporates the effects of strain, strain rate, stress state and temperature, and is based on the Perzyna type viscoplastic model. The viscoplastic function is a coupling of two proposed hardening functions accounting for the strain hardening and the effect of the martensitic transformation. The model successfully represents the four TRIP steels under the prescribed conditions using the determined parameters. / La transformation martensitique induite par déformation plastique (TRIP) est un important phénomène durant lequel la phase austénitique résiduelle métastable se transforme en martensite sous l’effet de contrainte ou de l’écoulent plastique. Ce phénomène a été mis en relief pour les aciers austénitique durant les années 70 et a été étudié en large pendant deux décennies pour comprendre sa complexité. Plus récemment, le même phénomène a été utilisé pour les aciers faiblement allié contribuant à une dualité d'augmentation de la résistance mécanique et de la ductilité. Le potentiel complet de ce genre d’acier est à découvrir dû à la complexité du matériel et du phénomène de sa transformation et sa dépendance sur plusieurs facteurs et conditions physiques ainsi que sur leurs réactions entre eux.Dans cette thèse, les caractéristiques métallurgiques et mécaniques de quatre acier, faiblement allié, multiphasé avec effet TRIP ont été étudies dans des circonstances imitant ceux constates lors d'un accident de véhicule. Ceci est accompli durant des essais de laboratoire où on varie la quantité et la vitesse de déformation, le taux de contrainte et la température qui sont des facteurs affectant la transformation et les caractéristiques mécaniques de ce métal.Un modèle constitutif phénoménologique pour la prédiction de la réaction de ces quatre aciers aux déformations de basse et haute vitesse est propose. Ce modèle viscoplastic, basé sur celui de Perzyna, prévoit les réactions dû au changement de la quantité et de la vitesse de déformation, le taux de contrainte, ainsi que le changement de la température. Le modèle prévoie avec succès les quatre types d’aciers TRIP sous les conditions décrites en utilisant les paramètres constitutifs déterminés.

The transition from deflagration to detonation is studied by focusing on the actual final process, i.e. the onset of detonation itself. The high speed deflagration prior to transition is obtained by suppressing the oscillatory structure of a detonation first. A theoretical model is developed to analyze the resulting deflagration complex which shows that it propagates close to half the CJ detonation velocity with the deflagration slowly separating from the leading shock. These high speed deflagrations thus obtained just prior to transition to detonation as well as the highly turbulent fast deflagrations that have been observed prior to transition in earlier studies are shown to be CJ deflagrations where the propagation velocities are governed by energetics rather than the flow structure. / To understand how the nonsteady behavior of detonations may affect the transition process, the one-dimensional pulsating detonation is analyzed by computational studies. The time averaged solution of the non-overdriven detonation over a cycle is found to recover the steady CJ solution and the independence of the far rearward boundary condition is demonstrated for the activation energies studied. The self-oscillatory nature of the detonation also plays a key role in the maintenance, failure, and re-establishment of the detonation structure. To study the onset of detonation, the high speed deflagration obtained by failing the detonation is subsequently perturbed with periodic disturbances to stimulate transition. The numerical simulations show that the perturbations undergo a frequency selective amplification process to accelerate transition where the optimal frequency is related to the chemical reaction time of the detonation. The existence of optimal perturbation frequencies to stimulate transition is also observed in the experimental investigation carried out, although its value appears to depend on the channel dimension. Based on the oscillatory and frequency selective nature of the detonation phenomena, an oscillator model is proposed. An equation that has the basic features of a mechanical oscillator has been derived for the pulsating detonation. The proposed oscillator concept indicates the need to examine detonation phenomena from the point of view of a resonant oscillator.