• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 17736
  • 1751
  • 1001
  • 529
  • 529
  • 529
  • 529
  • 529
  • 528
  • 439
  • 249
  • 167
  • 133
  • 63
  • 29
  • Tagged with
  • 25838
  • 25838
  • 3715
  • 1908
  • 1704
  • 1699
  • 1470
  • 1470
  • 1009
  • 1008
  • 975
  • 911
  • 862
  • 791
  • 782
  • 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.

Power performance, flow behaviour and excitation response of canted blades for a vertical axis wind turbine

Armstrong, Shawn 02 1900 (has links)
<p>The ability of vertical axis wind turbines to operate effectively in the presence of highly unstable, turbulent wind flow patterns makes them ideal candidates for small scale applications in urban environments, where enatic wind flow patterns are quite common. Their axisymmetric nature allows for wind energy extraction during conditions of rapidly varying wind direction, and their base mounted generator location permits relatively easy maintenance, making them a more suitable design for small scale urban installations as compared with traditional horizontal axis turbines. Wind tunnel experiments were canied out on a small scale, high solidity, three-bladed Danieus wind turbine with canted (tilted) blades. The effects of preset blade pitch (β =+2.5°, -1.5°, -3.5° and -5.5°) and of aerodynamic fences were investigated at high Reynolds numbers (>500,000) for their effect on power performance while simultaneously characterizing the flow behaviour on a section of the inner blade surface using Mylar tufts and a shaft-mounted video camera. The excitation response of the turbine was also measured. The results are compared to a set of similar straight blades.</p> <p>The results of pitching the canted blades show that the power performance increases up to C<sub>Pmax</sub> =0.28 for increasing outward blade pitch, to a best observed pitch of β = -3.5° after which the power performance decreases. Canted blades show acute sensitivity to inwards pitch where the power coefficient dropped to C<sub>Pmax</sub> =0.06 at β =<br />+2.5°. The power coefficient observed for canted blades was C<sub>Pmax</sub> = 0.29 at 9 m/s wind speed which was slightly higher than C<sub>Pmax</sub> = 0.26 measured for the equivalent set of straight blades that were tested at the same preset pitch (β = -3.5°) at 10 m/s wind speed. The maximum power coefficient occurred at a higher blade speed ratio for canted blades ( λ =2.15) compared to straight blades (λ = 1.7) despite nearly identical solidities (σ = 0.45 for canted blades versus σ =0.43 for straight blades). Aerodynamic fences improve the power performance of canted blades to C<sub>Pmax</sub> =0.29 at 8 mls wind speed to and C<sub>Pmax</sub> =0.31 at 10 mls wind speed and reduce the speed at which peak power occurs to λ =1.9. Aerodynamic fences do not noticeably change the power performance of straight blades.</p> <p>Flow visualization using Mylar tufts attached to the inside blade surface indicated that canted blades experience reversed flow exclusively during the upwind pass of their rotation at peak power. Overall, canted blades experience less reversed flow than straight blades at the same blade speed ratio and only develop minor reversed flow during the downwind pass for blade speed ratios substantially below peak power where straight blades experience significantly more reversed flow. Aerodynamic fences further reduce the amount of reversed flow on canted blades, especially directly below the fence.</p> <p>Due to differences in the peak operating speeds and the primary natural frequencies of the wind turbine with canted blades and straight blades, a direct comparison of the excitation response of canted blades and straight blades is not presently possible. However, normalizing the data suggests that canted blades do show reduced excitation response over straight blades.</p> <p>This study shows that the Current set of canted blades produces acceptable power levels, with the potential for further refinements to improve performance, and suggests that reduced excitation response can be achieved with canted blades.</p> / Master of Applied Science (MASc)

Modeling. System Identification and Control of a Belt Drive System

Zhu, Shenjin 03 1900 (has links)
<p>Belt drives have been serving the industry for a long period. Certain features of belt drives such as slippage, tension fluctuations, and sliding of the belt on the pulleys lead to highly nonlinear deformation, large rigid body motion, dynamical contact with sticking and slipping zones and cyclic tension. The performance of motion control for belt drives is important in many industrial fields and is affected by these factors. Advanced control can improve robustness of belt drive and result in a faster dynamic response and more accuracy. The Purpose of this project is to develop a mathematical model of an experimental belt drive system through physical modeling and system identification. This model is then used for the design of an advanced robust discrete-time controller. An extensive literature review is provided, covering modeling and control of belt drive system as well as sliding mode control (SMC) theory. Physical modeling is carried out for an experimental system followed by system identification. Both the physical and the identified models are used to analyze and investigate the characteristics of the system. Different control approaches such as discrete-time proportional integral derivative (DPID) and discrete-time sliding mode control (DSMC) are designed and implemented. The results are compared and conclusions are drawn from both control approaches.</p> / Master of Applied Science (MASc)

A Hybrid Thermoelectric Cooler Thermal Management System for Electronic Packaging

Russel, Kamrul I. 02 1900 (has links)
<p>Conventional cooling techniques, such as the use of heat pipes and forced convective cooling can be inadequate for many high performance electronic chips or when the operating ambient temperature is high. In such cases, there is a need for active cooling of the chip to keep its operating temperature below the design point. Thermo-Electric coolers (TEC) provide an attractive option in such instances and have been developed and used for thermal management in electronic packaging systems. Such systems, however, can have a low overall coefficient of performance since the TEC needs to be kept on even at low heat load conditions. In this thesis a hybrid thermal management system is considered that incorporates a TEC based active path in parallel with a conventional heat pipe based passive path. A thermal resistance network model is developed for the hybrid system that takes into account the governing thermo-physical equations for the TEC. The advantage of this hybrid system is that the passive path can transport the heat from the chip at moderate thermal conditions keeping the TEC electrically off while the TEC modules can be turned on when.the conditions become adverse. A higher overall system coefficient of performance can be achieved compared to a system consisting of only TEC module(s). One important design parameter is the fraction of the total heat sink area dedicated to each path, which will depend on the rated heat dissipation from the chip, thermal resistance of the entire heat sink and the operational ambient temperature. Controlled experiments were performed to validate the hybrid thermal management model for an example case of electronic package. The experimental facility consisted of a flexible heater to simulate the chip. The heat sink in the experiments was a cooling loop and the ambient temperature was controlled by changing the temperature of the water flowing through the cooling loop. The thermal resistance of the heat sink was simulated by acrylic glass. Experiments were performed for different fraction of the heat sink area dedicated to the heat transfer paths for a range of ambient temperatures. An operating envelope was presented to compare different hybrid thermal management configurations with a heat pipe based passive system and an only TEC system. The model predictions were in good agreement with the experimental results. Parametric studies were performed to analyze the effect of different variables on the system performance. The hybrid model can be used for other thermal management systems involving TEC modules.</p> / Master of Applied Science (MASc)

Design and Characterization of a Dual Electro-Hydrostatic Actuator

McCullough, Kevin January 2011 (has links)
<p>Actuation of flight surfaces in aircraft have evolved over the last century from systems using simple mechanical linkages actuated by the pilot to complex electronic systems that maneuver large loads and have some form of redundancy. The latest form of flight surface actuation uses Power-By-Wire (PBW) systems, which are modulated, lean and fault tolerant actuators embedded in the flight surface that require only the attachment of power and control wires. This research will focus on a specific form of PBW system called an Electro-Hydrostatic Actuator (EHA), which is seen on modern aircraft such as the Lockheed F-35 Lightning and the Airbus A380.</p> <p>An EHA is a closed-loop form of hydraulic system which controls an actuator's movement by routing fluid to it via a fixed-displacement pump attached to a servomotor. The two primary components of the EHA's hydraulic circuit are a bi-directional external gear pump and an actuator, but the system incorporates an accumulator, a bi-directional relief valve, a by-pass valve and a series of check valves for full functionality. The minimal components and the closed-loop architecture lend itself to be lightweight, modular and independent of other hydraulic systems on an aircraft.</p> <p>This research will focus on developing a design based on a dual EHA system used for the rudder of the F-35. The design objective is to reduce the comparative weight. The dual EHA allows for continued actuation of the airfoil in the event that one of the EHA's malfunction. The design produced in this research incorporates a new inner-circuit which allowed the system to be 12% lighter than the F35 rudder EHA. A prototype developed from this design was produced but was augmented with additional components that allow for simulation of fault conditions in the future. With a prototype produced several experiments were performed to determine the level of internal leakage and damping inside the system. Experiments showed that internal leakage increases linearly with the increase of back pressure on the pump and that the bulk of the leakage occurs at the pump itself. Experiments also showed that the damping in the system is non-linear and that it is best described by a LuGre friction model.</p> <p>Black-box system identification techniques were applied to the EHA to determine piece-wise linear models. These trials showed that the non-linear friction as well as the seals in the actuator forced the system to have two major piece-wise linear regions. These experiments also showed that when the mean velocity of the actuator increases so does the system bandwidth.</p> <p>Enclosed in this dissertation are details of the design of the dual EHA and the experimental results performed on it.</p> / Master of Applied Science (MASc)

On the Application of the Finite Element Method to Three-Dimensional Incompressible Potential Flow

El-Shammaa, Sedky A. 08 1900 (has links)
<p>This thesis describes the application of the finite element method to three-dimensional potential flow. The flow is assumed to be steady and incompressible. The flow region is simply connected and has complicated geometric boundaries. The boundary condition is of the Neumann type, or mixed Dirichlet-Neumann type. The finite element method presented provides an economical solution for the problem which could be difficult to solve using other methods.</p> <p>A versatile computer program was developed and used for solving three specific problems of flow around bends. One of the three problems had a known two-dimensional exact solution. The results obtained for this problem are in good agreement with its exact solution. The computer program can be utilized to solve similar problems, subject to the same governing equations and boundary conditions, in related fields such as electrostatics and heat conduction.</p> / Master of Engineering (ME)

Formability of Aluminum and Steel in Drawing Square Cups

Cloke, Terrance William 05 1900 (has links)
<p>A series of mechanical formability tests were performed on an aluminum-killed steel and five aluminum alloys. Three of the aluminum alloys exhibited strength levels and strain hardening abilities equal to or better than those of steel, but had very low fracture strains. The other two aluminum alloys had low strength but formed reasonably-well, except for negligible strain hardening ability of one of them. All of the aluminum alloys exhibited planar anisotropy detrimental to deep drawability.</p> <p>Tooling for deep drawing 2" wide square cups was designed and constructed. Tests were performed to find a suitable lubricant for square cupping tests and a combination of a heavy gear lubricant and polyethylene film was selected.</p> <p>Tests with the square punch and die set confirmed the results of the mechanical tests. The steel produced the deepest cups while height of cups drawn from the high strength aluminum alloys was severely limited by brittle fracture in the corner walls.</p> <p>Careful blank development proved to be a definite asset in square cup drawing. The best results were obtained with blanks designed to produce flat-topped cups but some application of blanks with extra material at the corners may be useful for materials exhibiting low fracture strains.</p> / Master of Engineering (ME)

Analysis and Optimization for Humane trap Design

Yi, Young-Joon 04 1900 (has links)
<p>The stirrup type spring that is used in the Conibear series of trans was analyzed and new springs for this type of trap were designed utilizing the non-linear optimization technique.</p> <p>The Jacob trap concert combined with the concept of a swinging interior mechanism for animal control was developed and optimized and four prototypes were manufactured and evaluated.</p> <p>Analytical methods for predicting the theoretical energy of closing Conibear and Jacob trans at various jaw openings were developed.</p> / Master of Engineering (ME)

Vibration Analysis of Plates, Shells and Bladed Rimmed Discs using the Transfer Matrix-Finite Element Method

Mohammed, Adel Ali Mohammed 12 1900 (has links)
<p>In recent years, the vibration problems associated with turbine blades have become of increasing importance. Blades in a gas turbine can fail if they are subjected to alternating forces having certain frequencies. Thus a need has arisen for accurate determination of these dangerous frequencies, so that the possibility of failure occurring during running can be avoided.</p> <p>This thesis presents a numerical method to predict the frequencies which must be avoided in the design of gas turbines. The accuracy of the method is tested by using it to solve some vibration problems for which analytical or experimental results are available.</p> / Doctor of Philosophy (PhD)

Tool Wear in End Milling Slots

Vashishta, Kumar Swatantra 02 1900 (has links)
<p>This thesis records an investigation of tool wear in milling slots with carbide-tipped and high speed steel end milling cutters as well as the development of the equipment used. The study is limited to one conventional material (mild steel) and one difficult-to-machine alloy (multimet) only.</p> <p>The first four chapters present a general review of machinability of materials, description of tool materials and various mechanisms of tool failure. Discussion of problems related to the machinability of heat resistant alloys as well as a discussion on machining under interrupted cutting conditions are included. The theories described are used in interpreting the experimental results.</p> <p>The fifth chapter describes the development of a Quick-Stop Device. This device is used in metal cutting research to rapidly reduce the velocity of the cutting tool relative to the workpiece to zero. The device enables investigations to be made of the geometrical and metallurgical behaviour of the chip as it is born.</p> <p>In Chapter VI the effect of various cutting conditions on the development of the tool wear while end milling steel as well as multimet is analyzed and optimum cutting conditions for end milling the two materials are recommended.</p> <p>In order to try to explain some of the phenomena observed. Turning experiments simulating previous milling operations were carried out and are described in Chapter VII. Here it was possible to separate the aspects of thin and thick chips from the aspects of interrupted cutting. The results of these tests indicate that the thin portion of the chip obtained at the entry and exit of end milling cutter affects tool life much less than the thick part of the chip. However, even these tests did not explain why it was rather the total number of cut interruptions than the actual cutting time which influenced tool life. Further research will be necessary in looking into both the mechanical and thermal shock aspects.</p> / Master of Engineering (ME)

Nucleation Site Activation in Saturated Boiling

Shoukri, Shoukri Mahmoud Mamdouh 03 1900 (has links)
<p>An experimental investigation is presented for boiling of distilled water at atmospheric pressure on a copper surface having three different surface finishes of 16, 5 and 4 v inch CLA. Activation of the nucleation cavities under three different levels of heat flux for each surface was investigated. The measured active cavity radii showed good agreement with the active site radii as predicted by both the Hsu and Han and Griffith models. As a result of this investigation it was apparent that small cavities were able to entrap vapour residue and be activated by their neighbours and that the reason for incipience delay as reported in the literature was due to the nonexistence of sufficiently large cavities with the prerequisite residue of gas or vapour.</p> <p>The correlation suggested by Brown relating (N/A)rc as a function of rc in the form (N/A)rc a (l/rc)ⁿ was confirmed. On the basis of this work, it is recommended that the parameter group [2o Ts/Pv hfg(Tw-Ts)] be used to characterize a boiling surface.</p> / Master of Engineering (ME)

Page generated in 0.2137 seconds