<p>An analytical and experimental study of bubble waiting time for dichloromethane boiling on a glass surface is reported in this thesis. Bubble waiting time data for boiling at heat fluxes of approximately 8000, 10000, 12000, 14000, 16500 and 19000 BTU/hr ft² and subcooling values of 1.6, 14.7 and 30.0 ºF is presented.</p> <p>In as much as bubble nucleation theory formulated on the basis of diffusion of heat to the thermal layer predicted results for bubble waiting time that were inconsistent with experimental data, a bubble nucleation theory incorporating both diffusion and convective transport of heat to the liquid in the vicinity of active sites was developed. The bubble waiting time results predicted by this theory agreed very well with experimental observation and therefore the evidence suggests that the convective contribution of heat transfer to the liquid layer adjacent to the heat transfer surface is a significant parameter in bubble nucleation.</p> / Master of Engineering (ME)

<p>Tube failure due to excessive flow-induced vibrations is a major concern with regards to the operation of heat exchangers in nuclear power and chemical process plants. Typical consequences include unplanned and expensive plant shutdowns to plug the failed tubes. Fretting wear resulting from tube/support impact is considered as a major contributor to tube failure. Impact forces, which occur when tube vibration amplitudes exceed the local support clearance, play a vital role in determining tube wear. Turbulence is one of the possible excitation mechanisms which can drive tube vibrations and is of particular concern in heat exchangers. Unlike other excitation mechanisms, turbulence has a persistent effect and thus determines the long term reliability of the heat exchangers. To address these issues, a point contact algorithm describing the tube/support interaction was implemented in an in-house finite element program and validated by several published examples. Pseudo-forces were utilized in conjunction with modal superposition in solving the nonlinear equations of tube motion. The equilibrium equations were solved iteratively to calculate the contact forces required to oppose any tube/support overlaps. The impact model was further modified to consider more realistic tube/support contact configurations. The new model considers a finite support width. The contact forces arising from the tube/support overlap are due to two different contact situations that may be encountered (point and segment contact). A distributed stiffness along the tube/support interface was utilized to model the segment contact. The resulting contact pressure was calculated using the displacement profile along the contact segment. The general point contact model considers any tube/support overlap that may occur between the principal contact node and the neighbouring node. Time-domain simulations of the nonlinear response of the tube are presented to determine the effect of various tube/support parameters on the system's vibratory characteristics. Special attention was paid to the effect of clearance enlargement due to fretting wear on the response of tubes in lattice-bar supports. The tube response, the impact force, and the contact ratio (ratio of the contact time to the total time) were analysed and presented in a dimensionless form. The dimensionless parameters utilized proved to be effective at collapsing all the data pertaining to different flow velocities over a single curve. This aids in identifying the role of support variables in influencing tube dynamics. Moreover, these parameters may also be used to scale the results in order to account for differences in geometrical and material properties. In addition, simulations were conducted to investigate the effect of the support type, the flow orientation, and the lattice-bar offset on the tube dynamics. The study indicates that some flow orientations, support types, and support offsets provide a favourable support geometry for higher normal work rates. This, in turn, increases susceptibility to fretting wear damage. These results provide new insights and a better understanding of the underlying phenomena of nonlinear tube behaviour in loose lattice-bar supports.</p> / Doctor of Philosophy (PhD)

<p>In current industrial practice, the transformation of Computer-Aided Geometric Design surfaces into Computer Numerical Control (CNC) machine tool axis commands is performed with the aid of Computer-Aided Manufacturing software and a closed CNC machine tool controller. The advent of new technologies such as Open Architecture Control has enabled the rethinking of motion command generation. This thesis describes a five-axis motion command generation architecture and algorithms in which a parameterized tool-path is interpolated off-line and the inverse kinematics mapping is performed in real-time, on the CNC controller. This architecture eliminates the need for time consuming repost-processing of the tool-path in the event of kinematic changes and additionally introduces the benefits of parametric splines with controlled feedrate. To deterministically attain a near constant feedrate tool-path, near arc-length parameterized splines are prepared off-line. The C2 position spline which is near arclength parameterized improves on the previously reported research. The orientation unit vectors are interpolated with a C 2 spherical Bézier spline. These two splines are then synchronized by means of a monotonic reparameterization spline. This results in reduced effective feedrate oscillation. The interpolated tool-path and axis commands are demonstrated to be smooth and C2 continuous. To cope with actuator saturation, a feedrate interpolation algorithm is developed which ensures C2 continuity but allows the feedrate to be adjusted as needed. The developed algorithms were simulated for two tool-paths and two five-axis machines tools. A test part was cut to demonstrate geometric correctness.</p> / Doctor of Philosophy (PhD)

Experimental and numerical investigations have been conducted to study the mechanisms involved in the electrohydrodynamic (EHD) induced flow and heat transfer augmentation of two-phase systems. The experimental study involved tube-side boiling heat transfer of the environmentally friendly HFC-134a in a single-pass, counter-flow heat exchanger 1.5 m in length, 12.7 mm O.D., 10.92 mm I.D., with a 3.18 mm rod electrode. The electrode position was varied from a concentric geometry to an eccentric geometry offset vertically from the centerline by ±2.73 mm. The applied voltage was 0 kV to 8 kV DC or 0 kV to 24 kV peak to peak AC (60 Hz and 6.6 kHz). Experiments conducted for the eccentric geometry have provided evidence that through the establishment of the appropriate electric field distribution, a desired change of flow regime will occur to augment the heat transfer rates at significantly lower voltage levels and pressure drop penalties. These results were based on the interpretation of the finite element results of the electric field distribution for the arrangement under investigation. The experiment has shown that when the electrode was positioned eccentrically +2.73 mm from the centerline, a 160% enhancement in heat transfer coefficient was observed under the application of a 2 kV DC voltage while the pressure drop increase was only 1.2 fold. Through the evaluation of the dimensionless criterion for EHD induced effects, electric field distribution analysis, EHD flow regime transition criterion and local and overall parametric analysis, the present investigation has shown that the developed electric body forces lead to a reduction in the thermal boundary layer thickness, increased convection, enhanced boiling dynamics and interfacial instabilities that can result in a phase redistribution. The consequence of this flow regime transition is the potential for significantly enhanced heat transfer rates at the wall, with only minimal increases in pressure drop. (Abstract shortened by UMI.) / Doctor of Philosophy (PhD)

<p>A generic mechanistic approach for simulating multi axis machining of complex sculptured surfaces is presented. A generalized approach is developed for representing an arbitrary cutting edge design, and the local surface topology of a complex sculptured surface. A NURBS curve is used to represent the cutting edge profile. The local surface topology of the part is defined as those surfaces generated by previous tool paths in the vicinity of the current tool position. The local surface topology of the part is represented without using a computationally expensive CAD system. A systematic prediction technique is then developed to determine the instantaneous tool/part interaction during machining. The methodology employed here determines cutting edge in-cut segments by determining the intersection between the NURBS curve representation of the cutting edge and the defined local surface topology. These in-cut segments are then utilized as integration limits for a comprehensive force modeling methodology. A systematic model calibration procedure that incorporates the effects of varying cutting edge geometry, cutting speeds, and feed rates is developed. Experimental results are presented for the calibration procedure. Model verification tests were conducted with these cutting force coefficients. These tests demonstrate that the predicted forces are within 5% of experimentally measured forces. An enhanced approach for dynamic mechanistic modeling for multi-axis machining is developed. The dynamic process simulation methodology is presented as a continuous solution for complex sculptured surface machining. The simulation results demonstrate how the continuous dynamic process simulation methodology is capable of predicting the cutting force and tool deflection for variable tool/workpiece immersions that occur during complex sculptured surface machining operations. The generic simulation approach for multi-axis machining has been demonstrated as a process optimization tool. Feed scheduling was used to demonstrate the process optimization for multi-axis machining. A feed scheduling methodology for multi-axis machining was developed. A case study for process optimization of machining an airfoil-like surface was used for demonstration. Based on the predicted instantaneous chip load and/or a specified force constraint, feed rate scheduling was utilized to increase metal removal rate. The feed rate scheduling implement at ion results in a 30% reduction in machining time for the airfoil-like surface without any sacrifice in the surface quality or part geometry. (Abstract shortened by UMI.)</p> / Doctor of Philosophy (PhD)

<p>In shallow parts it is important to obtain strain over the face of the part if a satisfactory part is to be produced. The strain distributing formability of materials is an important parameter influencing the amount of face strain in shallow parts. Strain distributing formability is not well defined or measured.</p> <p>The increased use in automobile components of high strength to weight materials such as dual phase steels requires greater precision in ranking materials for formability if these steels are to replace the conventional low strength steels.</p> <p>In this work an analytical modelling technique simulating a shallow part was developed. The technique was then used to examine how various parameters (geometric, material, and friction) affect the face strain in a shallow part.</p> <p>An experimental rig was designed and constructed which simulated a simple shallow part. The strains in the part were measured and used to verify the accuracy of the analytical modelling as well as give some indication of the friction conditions in a pressing operation. The experimental bottom strains are a possible means for ranking material formability in shallow pans. This ranking method and other methods based on tensile test data are discussed.</p> / Master of Engineering (ME)

<p>High Speed Servo Control of Multi-Axis Machine Tools, is concerned with maintaining tight position control at high feed rates, in the presence of disturbances generated by the cutting process. This is an important goal due to general advances in machining technologies, as well as economic pressures in specific industries. In this thesis a feed rate planning method, and servo loop control law are developed which explicitly account for the dominant machine tool servo characteristics, including actuator saturation. The feed rate planning method developed, 'Minimum Time Path Optimization' (MTPO), enables coordinated motions to be planned with near maximum utilization of servo capabilities (a reserve must be left to handle modeling error, and disturbances). The result is a significant reduction in servoing time without sacrificing path accuracy when compared to fixed acceleration and velocity limit path planning, or significantly reduced path error, when compared to fixed feed rate planning (assuming equal total time time). The servo loop level controller developed, Minimum-Time Tracking Control (MTTC), focuses on the primary sources of path error in high-speed servoing applications, specifically, limits on amplifiers, system inertia, and damping. This controller is relatively simple to compute, making it suitable for high speed servo control. MTTC's advantages are most clearly seen in its consistently superior disturbance-rejection properties. MTTC is shown to regulate steps of various sizes better (faster/less over shoot) than Generalized Predictive Control (GPC), H∞ , or Proportional Derivative (PD) controllers. It is also shown to respond more linearly in magnitude, and phase (unity gain, zero lag) to sin waves at various frequencies. A periodic observer is developed and implemented which significantly improves the rejection of cutting disturbances. Given that the major source of disturbances is the cutting process, an encoder on the spindle is used to synchronize compensation, with the disturbance. The instantaneous disturbance is estimated as the difference between the predicted acceleration, and the achieved acceleration. This estimate is then averaged as a function of spindle position, over successive spindle revolutions. A linear servo motor is constructed to investigate commutation strategies which allows each winding of a permanent magnet linear motor to be driven separately. This enables commutation strategies to be implemented which reduce the heat generated in the coils of the linear motor, increasing the continuous holding force of the motor by approximately 18%. A PC based Open Architecture Control (OAC) with soft motion control is developed which provides low level openness (All calculations including closing servo loops are performed on the PC, no special purpose motion control card is used.). This system enables the developed controllers, observers, and commutation strategies to be implemented in a cost efficient manner. It also eliminates many of the machine controller limitations which make path planning and computing difficult. Specifically, it enables the entire part path to be planned and computed in advance, stored, and executed, or played back in real-time. This eliminates the requirements of bounded execution times, and the difficulty of representing data in an intermediate form.</p> / Doctor of Philosophy (PhD)

<p>The problem of transporting steel billets from the No. 3 Bloom and Billet Mill to the No. 2 Rob Mill of The Steel Company of Canada is dealt with in this report. An original solution is proposed in the form of amphibious vehicles playing a water route in Hamilton Bay between the two mills.</p> <p>The following Study will prove the feasibility of such a scheme.</p> / Master of Engineering (ME)

<p>This thesis reports on the investigation of flow induced vibration in heat exchanger tube arrays. This work is in support of nuclear steam generator design, where attention is focussed on the tubes in the upper U-bend region which are subjected to cross-flow, and are therefore most susceptible to the destructive effects of flow-induced vibration. Results for this study are reported for a dynamically scaled model tube array in a parallel triangular layout, with a pitch over diameter ratio of P/D = 1.44, mounted in a clamped-free arrangement. This tube bundle was subjected to single and two-phase cross-flows of refrigerant R-11. The main motivation of this work is to present experimental results on fluidelastic instability, the mechanism that usually causes the most damaging vibrations, and to make comparisons with other data on the basis of non-dimensional similitude parameters to determine the effect of using different fluid mixtures to simulate the actual steam-water flow in the steam generator. A new method is proposed for calculating the average fluid density and equivalent flow velocity of the two-phase fluid, using a newly developed void fraction model which accounts for the difference in velocity between the gas and liquid phases. The fluidelastic data of several researchers, who used a variety of fluids, is re-examined using this new void fraction model and the results show a remarkable difference in trend between two common flow regimes, bubbly and intermittent flow. The latest flow regime map, developed by other researchers for predicting the two-phase flow regimes in the shell-side cross-flows in tube bundles, was applied to the fluidelastic results. This analysis showed that the sudden change in stability behavior which appeared in various data sets were directly related to a predicted change in flow regime from bubbly to intermittent flow. The two-fluid model used in the fluidelastic data analysis was developed by the present author from experimental measurements of void fraction in the horizontal tube bundle using the gamma densitometer. Measurements of the damping effect of two-phase flows were obtained in the present study and are presented and compared with previous data using an existing analysis technique. Damping measurements showed that the tube damping peaks at about 75% to 80% HEM void fraction, and decreases at lower and especially higher void fraction. The turbulence buffeting response of the tubes was measured and from this the non-dimensional spectrum of turbulent forces was determined and compared with existing data. In single phase flow, the data of the present study appears to plot higher than the extensive data points of Taylor et al. (1996), but are mostly within the upper bound determined by Taylor and Pettigrew (1999). In two-phase flow, the turbulent forces were analysed according to the new data reduction method of deLangre and Villard (1998). (Abstract shortened by UMI.)</p> / Doctor of Philosophy (PhD)

<p>A methodology for quasi-static error correction by compensation for an intrinsic Coordinate Measuring Machine (CMM) is proposed and tested in this thesis. It consists of three major parts. In the first part includes a systematic approach to machine kinematic modelling. Using this approach results in an analytically based, forward kinematics model of the machine including its errors. In the second part, the model error functions are identified, at the constant thermal state. At a later stage of the research, error functions identification at varying thermal states. The third part of the proposed methodology includes the actual utilization of the model in a compensation strategy to correct for the machine errors. To visualize the effect of the proposed methodology, the performance of the CMM is evaluated using the standard ASME B.89 test before and after compensation for its errors in the constant thermal state. Dramatic improvements are obtained reducing the machine error in measurement by 93%. A modified version of the B.89 standard incorporating the thermal state of the machine is used to test the machine performance at varying thermal states. Improvement of the CMM performance by reducing the volumetric error by 97% is obtained. The research was expanded by applying the proposed methodology to CMM contouring. Regression analysis was proposed for the models. Thermal sensors were used to provide information to update the models. The CMM behavior was tested through simulation in tracking the diagonals of its work volume. Remarkable improvement in the tracking errors reduction is observed. Results obtained show an improvement in the CMM performance to a level close to machine resolution.</p> / Doctor of Philosophy (PhD)