<p>Variational methods using the least action principle are used to set up equations for the vibration of systems. Using variational methods, finite elements of structures can be formulated on the space time domain to allow calculation of transient vibratory response to initial conditions and forcing functions. This work attempts to systematize such formulations, discuss limitations in the methods, and compare the accuracy of the two simplest methods to conventional finite difference techniques. Examples are given for single degree of freedom systems, the stretched string, simply supported beam, and plate. No method superior to the Newmark ß method has been developed.</p> / Master of Engineering (ME)

<p>The benefits of automating assembly sequence generation include: (1) insuring that no potentially good assembly sequence is overlooked, (2) reducing planning costs, (3) accelerating the analysis of the economical impact of different design solutions, (4) standardizing and improving the quality of the produced plans, and (5) contributing to achieving autonomous assembly systems. Previous research in assembly planning focussed on the generation and evaluation of all possible assembly plans for the product under consideration. This thesis presents a graph-theoretic approach for simultaneously generating and evaluating products' assembly/disassembly sequence alternatives and producing an optimum assembly plan according to predefined criteria. It aims at improving the efficiency of the assembly planning process and producing optimal assembly/disassembly plans. The developed graph-theoretic approach enables the determination of assembly sequences which transform any arbitrary initial state of the product into any arbitrary final state. Practically, this means many different types of assembly problems to be handled uniformly. A product is described in terms of its components and the assembly relationships between them. This description lends itself to a graph representation, where vertices correspond to the set C of assembly components and edges correspond to the set R of assembly relationships. For a product with "n" components, the generation of an assembly sequence is mapped into the problem of finding a sequence of "n-1" mutually exclusive cutsets in the graph model and its subgraphs. Each cutset corresponds to a disassembly operation of the physical product which produces two smaller subassemblies. Assembly sequences are encoded in a directed graph of assembly states, representing the search space. Geometric feasibility and accessibility constraints have been developed to help reduce this combinatorial search space. Assembly-related criteria which guide the search to an optimal solution are described. They are: (1) the number of re-orientations, (2) parallelism among assembly operations, (3) stability of subassemblies, and (4) clustering of similar assembly operations. Integrating the evaluation of these criteria as the search graph gets expanded, enables the direct generation of an optimal disassembly sequence of a given product with respect of these criteria. Standard search methods, including breadth first, depth first, best first, A* and hill climbing, are used to guide the search towards a single and optimal assembly sequence. The A* method can generate optimal solutions without explicitly generating the whole directed graph of assembly states. An interactive computer tool, based on the above approach, was developed. GAPP--a Generative Assembly Process Planner uses various search methods to incrementally construct the directed graph of assembly states and generate optimal assembly/disassembly sequences. Examples of real products are included to demonstrate GAPP's use and potential for assessing assembly, disassembly, repair, maintenance, assembly of multiple products and assembly error recovery procedures.</p> / Doctor of Philosophy (PhD)

<p>Researchers in recent years have attributed the dynamic instability of certain hydraulic control devices (such as gates, valves, and seals) to a velocity dependent hydrodynamic load which is equivalent to a negative damping coefficient in the differential equation of motion. Such a model is not capable of predicting certain important features of observed check valve behaviour.</p> <p>A semi-empirical model for check valve self-excited vibrations is derived. The results show that the gross behaviour of this model is qualitatively the same as the experimental observations. Hence, the existence of a hydrodynamic load component in phase with displacement appears essential for the hydrodynamic load modelling.</p> <p>A general mathematical model is then derived from first principles. Closure of the hydraulic control device during vibrations and unsteady flow phenomenon including viscous losses are taken into account. The proposed model can be applied to any type of hydraulic control device with a jet-flow mechanism of excitation. Two applications for the model have been examined. Check valve and seal applications show that the model results are in reasonable agreement with the experimental observations.</p> / Master of Engineering (ME)

<p>An algorithm is presented for the solution of mechanical contact problems using the displacement based Finite Element Method. The corrections are applied as forces at the global level, together with any corrections for other nonlinearities, without having to nominate either body as target or contactor. The technique requires statically reducing the global stiffness matrices to each degree of freedom involved in contact. Nodal concentrated forces are redistributed as continuous tractions. These tractions are re-integrated over the element domains of the opposing body. This creates a set of virtual elements which are assembled to provide a convenient mesh of the properties of the opposing body no matter what its actual discretizaton into elements. Virtual nodal quantities are used to calculate corrective forces that are optimal to first order. The work also presents a derivation of referential strain tensors. This sheds new light on the updated Lagrangian formulation, gives a complete and correct incremental form for the Lagrangian strain tensor and illustrates the role of the reference configuration and what occurs when it is changed.</p> / Doctor of Philosophy (PhD)

<p>The results of an experimental and analytical investigation of the separation phenomenon in dividing annular two-phase flow is presented. Detailed experiments have been carried out with a steam-water loop to isolate the effects of flow split, inlet quality, inlet mass flux and branch diameter on the phase and pressure distribution characteristics in horizontal T-junctions. Through the set of measurements made in the experimental program, the phase separation and pressure distribution characteristics were shown to be strongly interdependent. Based on these measurements, a physical model describing the phase separation mechanism is presented. This physical model is then developed mathematically. A model to predict the dividing flow characteristics for annular flow in a T-junction is proposed consisting of mixture and vapor phase continuity equations, two pressure change correlations and a closure relationship. The pressure change from the inlet through the run of the T is modelled by way of a balance of axial momentum at the junction based on a separated flow assumption. The branch pressure change is modelled using a balance of mechanical energy for the branching flow consisting of reversible and irreversible components. In the development of the branch model, a new equivalent inlet density for the branching flow ($\rho\sbsp{1}{*}$) and a two-phase multiplier ($\Phi\sp*$) are defined. The closure relationship links the phase separation characteristics with the junction pressure changes. It involves a balance between pressure and inertia forces within the junction volume defining a dividing surface for each phase between the run and branch flows. The degree of phase redistribution is then determined using a well defined inlet flow distribution. The model is capable of predicting the experimentally observed phase separation characteristics from three independent studies of annular/steam-water and air-water flow in dividing T-junctions.</p> / Doctor of Philosophy (PhD)

<p>The problem considered is that of obtaining an optimum solution to large nonlinear engineering system by coordinated optimum solutions of smaller sub-systems. The technique produces a way of displaying graphically and numerically the trade-offs between each sub-system design objective and the sub-system joint design specifications. A nonlinear multi-variable fitting model is developed to represent the trade-off hypersurface. Shape, potential and advantages of the trade-off surfaces also are illustrated.</p> / Master of Engineering (ME)

<p>In this thesis, the damped free vibrations of composites are treated from the viewpoint of macromechanical analysis. Two damping models are developed, namely: the Viscoelastic Damping (VED) model and the Specific Damping Capacity (SDC) model. The important symmetry property of the damping matrix is retained in both models. A Modified Modal Strain Energy method is proposed for the evaluation of modal damping in the VED model using a real, instead of a complex, eigenvalue problem solution. Numerical studies of multi degree-of-freedom systems are conducted to illustrate the better accuracy of the method compared to the Modal Strain Energy method. The experimental data reported in the literature for damped free vibrations, in both polymer-matrix and metal-matrix composites, were used in the finite element analysis to test and compare the damping models. The natural frequencies and modal damping were obtained using both the VED and the SDC models. It was shown that the results from both models are in satisfactory agreement with the experimental data. Both models were found to be reasonably accurate for systems with low damping. Parametric studies were conducted to study the effects on damping of the side-to-thickness ratio, the principal moduli ratio, the total number of layers, the ply-angle and boundary conditions.</p> / Doctor of Philosophy (PhD)

<p>The experimental study of an inward radial flow turbine is described in this report. Preliminary tests of the turbine by United Aircraft of Canada Ltd. indicated that the isentropic efficiency was some 50% below the design target of 80% efficiency. In an effort to locate problem areas in the turbine design, the unit's response is examined under four different load conditions at speeds ranging from 10,000 to 75,000 RPM and pressure ratios from 1.2 to 2.4. The results of these tests are presented using a series of non-dimensional parameters typically employed in turbine and compressor design. From these parameters it is evident that the poor response of the unit is due to the high degree of exit swirl introduced into the primary diffuser by the "exducerless"turbine blades.</p> <p>The response characteristics of the unit are examined in the light of the experimental results, and explanations of various phenomena are offered.</p> / Master of Engineering (ME)

<p>The continuous emphasis placed on obtaining higher work outputs from Gas Turbines has led to the design of turbine blades having large turning angles.</p> <p>As part of a research program co-sponsored by the National Research Council and Pratt and Whitney of Canada Ltd., this work examined the aerodynamic behaviour of the root section of the highly curved turbine blade under investigation.</p> <p>An intermittant blow-down wind tunnel was used to test a two dimensional cascade of high turning angle turbine blades. The tunnel was modified to allow improved flow control at the desired operating conditions.</p> <p>A computerized scheme was developed whereby the two dimensional potential flow solutions could be obtained by merely specifying the cascade geometry and inlet flow. This allowed the direct comparison of theoretical and experimental blade surface pressure distributions. The effect of overall pressure ratio on the variation of exit gas angle and total head loss coefficient was also investigated experimentally.</p> / Master of Engineering (ME)

<p>The flow of jets in confining enclosures has significant application in many engineering processes. In particular, two jet flows have been studied; the impingement of axisymmetric jets in a confined space and a turbulent inlet wall jet in a confining enclosure.</p> <p>The impingement ofaxisynunetric jets in a cavity has been examined using<br />flow visualization, laser Doppler anemometry, and numerical simulations. When the<br />flow fIeld was examined under various geometrical and fluid parameters several flow<br />regions were found, depending on the geometrical and fluid parameters. Initially, a<br />steady flow field existed for all arrangements for Red < -90 but subsequent increments in the fluid velocity caused an oscillating flow field to emerge. The onset of the<br />oscillations and the upper limit of fmite oscillations were found to be a function of the<br />nozzle diameter to chamber dimeasion ratio. Although steady numerical simulations<br />predicted the steady flow field well. steady simulations of the oscillating flow field<br />over-predicted the peak axial velocities. The oscillating flow field is considered to be<br />a class of self-sustaining oscillations where instabilities in the jet shear layer are<br />amplified because of feed back from pressure disturbances in the impingement region.</p> <p>The turbulent wall jet in a cavity has been studied using flow visualization,<br />laser Doppler anemometry (LDA), particle streak velocimetry (PSV) and numerical<br />simulations. Instantaneous PSV measurements agreed well with time averaged LDA measurements. Two dimensional simulations using an algebraic stress turbulence<br />model (ASM) were in better agreement with the experimental data than two and three<br />dimensional simulations using a k - ɛ turbulence model in the wall jet region. A wall jet growth rate was found to be 54% higher than a wall jet in stagnant surroundings due to the enclosure boundaries.</p> / Doctor of Philosophy (PhD)