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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

A Study of an Adaptive Control Constraint System for Milling

Elbestawi, Abdel Aziz Mohamed 02 1900 (has links)
<p>This thesis deals with an adaptive control constraint system for end milling with constant force. The control criterion is to hold the force acting on the cutter at a value safely below the force which would break the cutter. This criterion is applicable to finish milling of complex shapes, typically of die cavities. The controlled variable is the command feed rate.</p> <p>Two other constraints were considered for the adaptive control system, namely: chatter and overload of the cutting edge.</p> <p>The work presented in this thesis was based on a homemade Computer Numerical Control (CNC) and Adaptive Control (A/C) System consisting of an NC retrofitted No. 4 vertical milling machine and an HP 2100A minicomputer.</p> <p>The operating characteristics of this system were examined both experimentally and by digital computer simulation. The analytical analysis of the A/C system concentrated on its behaviour as a servomechanism, i.e. mainly with respect to the speed of its response to step inputs and to its stability. In this analysis both the Laplace transform approach as well as a numerical simulation (State-Space approach) were used.</p> <p>In order to improve the system response to collision or step changes in cutting loads caused by abrupt changes in work surface contact area, special action strategies are presented. These strategies are allowed to operate for a limited time during impact before the system switches back to a slower acting (lower gain) strategy. This leads to improved reaction time whilst maintaining system stability.</p> <p>The A/C experiments were conducted using two different types of dynamometers for the on-line measurement of cutting force. Two different workpiece materials were used: Al. Alloy (95 BHN) and steel AISI 1020 (155 BHN). High Speed Steel end mills were used in all experiments.</p> <p>An experimental investigation of the chatter constraint was also carried out as well as a review of the basic features of the phenomenon of cutting edge overload.</p> <p>It is shown that the flexibility of the end milling cutters is beneficial in attenuating the overload in a sudden transient situation and it is also beneficial in attenuating chatter. These benefits are obtained for a certain range of diameters and lengths of cutters. Within this range constraints on feed rate for edge overload must be considered and outside of this range the chatter constraint has to be included.</p> / Doctor of Philosophy (PhD)
62

A Software System for Interactively Creating Three-Dimensional Free Form Surfaces

Badawy, Ahmed Kamal Aly 09 1900 (has links)
<p>A system for the interactive design of free form surfaces is presented. The system is best suited for creative design based on aesthetics, experience, or a number of empirical rules. The system provides the designer with a carefully integrated set of tools which permit a rapid and convenient creation of a curved 3-D surface of any type.</p> <p>In addition to the uniqueness of the overall concept, there are several innovative features. These include definition of a patch by 16 surface points only; surface modification by dragging nodes to any desired location with the light pen; and a powerful technique for defining patches using plane curves on sections.</p> <p>A new method for determining NC cutter path location is suggested using the developed system.</p> / Doctor of Philosophy (PhD)
63

Random Response of Articulated Road Vehicles

ElMadany, Mohamed Mohamed 05 1900 (has links)
<p>A method for determining and analyzing the linear dynamic response of the complex articulated vehicle structures to road surface undulations, represented as stationary Gaussian random excitations, is formulated. The procedure is used to estimate the influence of various parameters on the dynamic behviour of the articulated vehicle. In particular; the influence of vehicle suspension systems, load patterns, speed, and road characteristics on the ride comfort and ride safety is evaluated.</p> <p>An analytical method based on the equivalent linearization technique is developed in order to study the effect of the system nonlinearities on the ride behaviour of the articulated vehicle. The nonlinearties include dry friction, bump stops and wheel hop. The vehicle is treated as a discrete, nonlinear, time-variant, multi-degree-of-freedom dynamic system subjected to random road irregularities.</p> <p>An extensive review of the available literature is presented as background to the present work. The review provides details of various proposed methods of modelling the road surface undulations, and vehicle components as well as methods of performing the analysis necessary to obtain the vehicle vibrational response and assessing the ride quality.</p> / Doctor of Philosophy (PhD)
64

Characterization and Modeling of Rubbing Friction in a Motored Four-Cylinder Internal Combustion Engine

Sylvester, Jeffrey R. 04 1900 (has links)
<p>While many aspects of the internal combustion engine contribute to its fuel efficiency, internal friction warrants special attention due to the relatively large degree of losses it represents, as well as a nearly universal application to all engines. Internal friction is therefore an important consideration in the design of modern engines and will remain so in the conventionally powered and hybrid vehicles of the near future.</p> <p>Measurement and characterization of internal engine friction is a significant first step towards engine modeling, attempts to reduce friction, and further applications related to engine condition monitoring or control. In order to measure the friction losses internal to a Ford 2.0L 4-cylinder engine a dedicated dynamometer test stand was designed and constructed. This test stand allowed the direct measurement of the frictional losses encountered by the engine in the motored state from low to moderate speeds. This data was then used to update and fit a physical, component-based friction model to the engine. A complete engine model known as the mean value engine model (MVEM) was then augmented with the verified friction model for simulation of the running engine. Its predictions were compared to a limited amount of available fired-engine data, demonstrating a general fit which could be improved with additional data.</p> <p>The dynamometer test stand created is a viable tool for future engine friction testing, especially with partial engine disassembly or varying engine oil (operating) temperatures, or for future investigations of other rotating equipment.</p> / Master of Applied Science (MASc)
65

A Study of a General One-Dimensional Two-Fluid Critical Flow Model

Schwellnus, Carl January 2011 (has links)
<p>Accurate modelling of critical two-phase flow is important for the simulation of Loss-of-Coolant-Accidents in the nuclear industry and for the sizing of emergency relief valve systems in the chemical industry. A large body of experimental and theoretical work including the development of many models has been done over the last twenty-five years but as yet there is no one model which can accurately predict flow over a wide range of conditions which has found general acceptance. The purpose of this work is to examine the existing models, and using a general one-dimensional two-fluid model, investigate the various possible forms of the terms and their effects on the predicted results. The resulting computer model has six conservation equations plus a seventh for bubble growth in bubble flow. It allows for hydrodynamic as well as thermodynamic non-equilibrium and considers three flow regimes; bubble flow, churn flow, and annular flow. The model has improvements in the equations, interfacial terms, and interfacial constitutive relations. The best forms of the equations with some new developments were then used to predict the experimental results from several tests with a variety of inlet conditions and experimental setups. The range of conditions tested were inlet stagnation pressures of .2 to 6.6 MPa slightly subcooled or saturated, with diameters from .00125 to .0127 m. and lengths from .001 to 3.6 m. The length to dIameter ratios varied from .8 to 287. Comparison against pressure profiles shows good agreement and with one exception, the predicted mass fluxes are within -9 to +13 % of the experimental values.</p> / Master of Engineering (ME)
66

The Effect of the Inlet Boundary Layer on the Secondary Flow in an Annular Cascade

Shammaa, El S.A. 10 1900 (has links)
<p>The development of small gas turbine units with high specific output calls for the design and testing of rotor cascades with high turning blades. A major portion of the losses that occur in such cascades are associated with the secondary flow. The need for experimental data of highly loaded annular cascades can be readily seen from a review of the available literature.</p> <p>The objective of this study was to construct and test an annular test rig of special configuration particularly suited for high turning blades. The rig was an open circuit wind tunnel with inlet and exit ducts of hyperboloidal shape. The test facility provided a means for adjusting the inlet flow in the circumferential direction (to ensure periodicity) as well as controlling the inlet endwall boundary layers. The cascade tests were conducted at a Reynolds number of 4.73x10⁵ based on the blade chord. Extensive flow measurements were taken at the inlet and the exit from the cascade both in the main stream and the endwall boundary layers. The passage walls static pressure distribution was also measured. Maps of the exit flow parameters were presented for the total pressure loss coefficient, static pressure coefficient and the secondary flow velocity vectors. The averaged flow parameters were analysed and the losses were compared with several predictive correlations. The measured losses were found comparatively lower than the predicted.</p> <p>A flow visualization study was carried out using smoke in the air stream and oil film (lamp-black and kerosene) on the passage walls. The results thus obtained were consistent with the general flow picture depicted from the analysis of the measured data.</p> / Doctor of Philosophy (PhD)
67

Mathematical Modelling and Computer Simulation of Human Locomotion

Pal, George Thomas 09 1900 (has links)
<p>This study is a theoretical investigation of the process of human locomotion. It is restricted to the lower limbs and includes the major muscles of the legs.</p> <p>A mathematical model is presented incorporating some of the findings of earlier investigators of locomotion dynamics and of muscular control. The underlying hypothesis is that locomotion is an optimal control process governed by a minimum energy condition. Pontryagin's Maximum Principle is used to implement this optimality criterion. The model is then programmed for evaluation on a high speed digital computer.</p> <p>The results of the computer simulation are presented along with experimental verification of the findings. The close agreement between the two suggests that the model is an analytical tool that may be used as a foundation for programs of Functional Electro-Stimulation as aids for the physically handicapped.</p> <p>Included are further suggestions regarding the application of the model to other biomedical problems as well as recommendations for extensions of the work to broaden the scope of utility.</p> / Doctor of Philosophy (PhD)
68

Secondary Flow in an Annular Cascade of High Turning Angle Turbine Blades

Moustapha, Said H. 03 1900 (has links)
<p>Approximately half of the aerodynamic losses in a turbomachine blade row are attributed to cascade secondary losses. Looking at the existing literature on secondary flows, there is a lack of detailed experiments carried out on annular cascade of high turning angle turbine blades.</p> <p>The purpose of this investigation was to construct and carry out detailed experiments on a unique large scale annular cascade of high turning angle turbine blades. Cascade tests, at a Reynolds number based on the blade chord of 3 x 10⁵ to 6 x 10⁵, consisted of inlet and exit flow parameters traverses, blade passage pressure distributions and flow visualization. The results, presented in the form of contours and radial distributions, were analysed and compared with the results of previous investigations.</p> <p>The tests showed that the flexibility designed into the cascade rig has achieved the purpose of tailoring the inlet flow conditions according to the test requirements. The total pressure loss contours revealed a large single loss region at the middle of the blade passage. The yaw angle contours showed regions of significant flow underturning and overturning in the main stream. Good agreement was found between the measured cascade secondary loss coefficient and those calculated from the available correlations.</p> / Doctor of Philosophy (PhD)
69

Fluid Dynamic Evaluation in Models of Arterial Branches

El, Masry A. A. 09 1900 (has links)
<p>The purpose of this investigation is to determine experimentally the fluid dynamic field in models of arterial branching vessels and to identify the flow features which might influence the predominant occurrence of atherosclerotic lesions in such vessels.</p> <p>Flow conditions in four rigid-walled models representing the aortic bifurcation, iliac bifurcation, mesentric artery branch and renal artery branch are investigated over a Reynolds number range of 1000-4000 and a complete range of flow division between daughter vessels. Qualitative flow streamline patterns and quantitative definition of those flow conditions leading to flow separation are determined primarily at steady flow with a limited set of pulsatile experiments. The flow patterns observed are photographed using high speed cinephotography and a neutrally-buoyant tracer-particle technique. The flow streamline patterns in the four models are complicated and characterized by secondary flow motion. This motion is accentuated with increasing Reynolds number. Flow separation is inducible through alteration of flow division between daughter vessels or by an increase in the flow rate. Each of the four models has distinct combinations of flow rate and flow division ratio which give flow separation at the outside wall of one or both daughter tubes. The separated flows observed here display streamlines forming an open vortex with flow entering and leaving. The site of the separation point in the branching plane is approximately constant with the reattachement points occuring further downstream as Reynolds number increases and as the branch flow rate decreases.</p> <p>Shear rate distributions at the walls of the four models are measured using an electrochemical technique. This technique is based on an oxidation-reduction reaction at electrodes implanted in the wall. Distribution of wall shear rate of the branching site is very non-uniform, with high shear rate at the leading edge of the flow dividers. The shape of the shear rate curves are functions of the geometry, total flow rate and most importantly the flow division ratio. An unstable pattern of shear is found at the wall where separation is expected to occur. For pulsatile flow, the time-averaged rate of shear is not appreciably changed by frequency and amplitude of pulsation. The biological implication of the results is discussed with specific reference to the sites of atherosclerotic lesions found in man for these geometries.</p> / Doctor of Philosophy (PhD)
70

The Influence of Surface Conditions in Nucleate Boiling

Shoukri, Shoukri Mahmoud Mamdouh 05 1900 (has links)
<p>A theoretical and experimental study of the influence of surface conditions in nucleate boiling is presented. The surface conditions are represented by the density and distribution of the active nucleation sites as well as the size distribution of the cavities which constitute the nucleation sites.</p> <p>One of the important boiling parameters known to be a function of the nucleation cavity size is the frequency of bubble departure. A theoretical model is formulated to predict the bubble frequency as a function of the nucleation cavity radius as well as the surface superheat and liquid subcooling in which the time variations of the surface temperature throughout the bubble cycle are incorporated. Parametric study of this model shows that the frequency of bubble departure decreases with decrease of surface superheat and increase of liquid subcooling, a trend which agrees with the published data. It is also shown that smaller nucleation cavities are able to emit vapour bubbles with higher frequency than that corresponding to larger cavities. Experimental results obtained by boiling water and isopropyl alcohol on a single copper surface having two different surface finishes showed good agreement with the theoretical model.</p> <p>In addition, the concept of the bubble flux density is introduced. The bubble flux density is defined as the rate of bubble emission per unit area of the boiling surface and a method of evaluating it as a function of bubble frequency and active site distribution is proposed. A uniform correlation between the boiling heat flux and the bubble flux density is found to exist for a particular solid-liquid combination irrespective of the surface finish within the region of isolated bubbles.</p> / Doctor of Philosophy (PhD)

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