• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1
  • Tagged with
  • 206
  • 115
  • 112
  • 111
  • 110
  • 109
  • 109
  • 11
  • 10
  • 10
  • 8
  • 8
  • 7
  • 6
  • 6
  • 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.
41

Piston-cylinder dynamics in oil hydraulic axial piston pumps

Darling, Jocelyn January 1985 (has links)
No description available.
42

Characterisation of two phase releases

Pettitt, Glenn Nigel January 1990 (has links)
No description available.
43

Solutions to the Navier-Stokes equation set for spiral pipes

Mosley, Nile Spencer January 1996 (has links)
The research presented herein embodies three subject area specifically aimed at the investigation and application of the spiral geometry. These areas are: the derivation of a spiral coordinate system in E2; the formulation of a new metric suitable for spiral pipe structures; the numerical simulation of an incompressible viscous fluid flowing through spiral pipe structures. The spiral coordinate system is first derived and then proven admissible using differential geometry. Validation is achieved using the spiral coordinate system as an alternative transformation for mapping from Cartesian to Polar coordinates for the solution domain of the general wave equation from a square to a circular elastic membrane. Problems associated with curves that do not possess natural-parameterisation in terms of arc-length, and as such cannot use the standard form of the Frenet-Serrat formulae, are solved with the derivation of a generalized metric. This metric is presented and proven for use on an arbitrary shaped pipe of class 'n' and is especially suited for spiral pipe structures. The associated Christoffel symbols of the second kind are also derived and presented in association with the generalized metric for use with the tensorial form of the Navier-Stokes and continuity equations. Finally, the spiral coordinates system is extended into E3 for two types of pipe; the spiral conic and the spiral parabolic. The Continuity and Navier-Stokes equations are numerically solved for an incompressible viscous Newtonian fluid for these pipe structures with various inlet conditions and geometric constraints. A correlation is made with these solutions and solutions found for the helical pipe structure, the nearest equivalent to the spiral found in the open literature.
44

The influence of the accumulation of deformation on the failure of polyethylene pipe materials

Ward, Andrew L. January 1994 (has links)
No description available.
45

Steam air ejector performance and its dimensional parameters

Dandachi, Jaber M. A. January 1990 (has links)
This thesis reports a two part investigation of single- and two-stage ejector systems in which the primary fluid is steam and the secondary fluid is air. The first part is an experimental investigation. The vacuum created by the ejector is strongly affected by the distance between the steam nozzle outlet and the diffuser throat section. The relation between this distance, which is called in this thesis "the nozzle optimum distance (Lop)", and the geometrical and operating parameters of the nozzle and the diffuser were investigated and forms the object of this part of the thesis. The second part is a theoretical approach. The exit Mach number for the nozzle was found by using the one-dimensional gas dynamic equations together with the first law of thermodynamics. Also a two-dimensional approach using the Method of Characteristics was used to find the exit Mach number and the characteristic net of the flow from the throat to the outlet of the nozzle. Two computer programmes were written on the basis of these two different theoretical techniques and the comparison between the results for the exit Mach number found to be 95% in agreement over the pressure range of the experimental work. A computer programme was also written using the Method of Characteristics to find the shape i.e. the characteristic net and the constant density lines within the flow of the steam jet leaving the nozzle and entering the diffuser. It is believed that the jet diameter at the point where it meets the diffuser wall, which is called in this work "the optimum jet diameter (Dop)", is strongly related to the nozzle optimum distance (Lop). When the characteristic net for the jet is drawn, its point of interception with the diffuser wall can be found and then (Dop) can be measured. This diameter (Dop) was then related to the ejector dimensional parameters and the ejector operating conditions; an equation was found to predict the optimum jet diameter from this equation (Dop)e. Then the predicted optimum nozzles distance (Lop)e was determined by using this computer program where the characteristic net meets the diffuser wall at the calculated optimum jet diameter (Dop)e. Finally, the experimentally determined value of the nozzle optimum distance (Lop) was compared to the theoretically predicted value, and the average error was found to be 1.23%.
46

Factors controlling the performance of horizontal flow roughing fitters

Lebcir, Rabia January 1992 (has links)
Horizontal Roughing Filtration (HRF) is a pretreatment method used to remove excess turbidity and suspended solids of surface water fed into Slow Sand Filtration units, as these can only operate satisfactorily when the concentration suspended solids is below 25 mg/1 . A critical review and discussion of current pretreatment methods, HRF research and important filtration variables are presented together with a review of mathematical models of sand and roughing filters based on clarification and trajectory theories. A detailed historical review of head—loss theories, their development and adoption in multimedia filtration is given. I. Preliminary results from studies on a small scale HRF model suggested that: - A laboratory scale model must be over 1.2 m in length: 1.6 _in turned out to be acceptable. - An outlet chamber should be provided. — Sampling must be carried out in a two dimensional field. — Intermittent sampling is adequate. One of the main objectives of this research was to identify the Important variables affecting HRF, among velocity, temperature, particle size, particles density, arrangement of the gravel bed 'Coarse—Medium—Fine (LGF),Coarse/Fine—Fine—Coarse (SGF)§, and the bed depth. II. Experiments were conducted on a 1.6m filter scale model, using Fractional Factorial Design to identify the main variables. These were found to be particles size, velocity, and temperature. III. Further runs, using a suspension of kaolin, produced results which, upon analysis for suspended solids, turbidity, particles count, revealed that the efficiency decreases with increasing temperature and velocity and increases with increasing particles size. IV. Concentration curves along the bed enabled: — The development of the removal rate equation, — Defining the operating parts of the filter at various stages of the filtration, ' — The presence of density currents. V. Efficiency variations with the amounts of accumulated solids were monitored and revealed three main trends: a) Constant efficiency; b) Gradually decreasing efficiency; c) Increasing and then decreasing efficiency. - VI. Tracer tests showed the presence of dead zones, and - short—circuiting with either increased deposits or temperature. VII. Particles size analysis revealed that: a. The effect of velocity or temperature on the grade efficiency affects mainly suspended particles in water smaller than 10 pm and 7 pm for LGF and SGF respectively. For particles of larger diameters, an unknown repulsion phenomenon increasing with temperature rise was observed. b. The main mechanisms responsible for particles removal are sedimentation and hydrodynamic forces.
47

Bulge forming of tubular components

Hutchinson, Mark Ian January 1988 (has links)
The bulge forming process is a method for shaping tubular components using an internal hydrostatic pressure combined with a compressive axial load. Initial investigations involved carrying out an extensive literature survey to determine the components which could be formed and the effects of using lubricants and different tube materials. Die-blocks were designed to produce tee pieces, cross joints and off-set joints, and electronic on-line instrumentation was incorporated so that the forming pressures and loads could be accurately monitored. A series of tests were carried out in the forming of: (1) tee pieces, cross joints and off-set joints from copper tubes of two different wall thicknesses, (2) tee pieces using different types of plungers, (3) tee pieces using die-blocks coated with various lubricants, (4) tee pieces from aluminium, copper and steel tubes, (5) tee pieces using die-blocks with various branch radii. From the resulting components, formed with various combinations of internal pressure and compressive axial load, the limits for a successful forming operation were established. Further analysis of these components was then undertaken to evaluate the effects of the internal pressure and axial load on the bulge height and the wall thickness in the deformation zone. From these results, which have been illustrated graphically, the greatest effect on the resulting bulge can be seen to be the compressive axial load. Theoretical analyses are presented, which predict the wall thickness distribution around the bulge zone and also the axial loads required in the forming process. Comparison of these predictions with the experimental results shows fairly good agreement.
48

The hydraulic bulge forming of tubular components

Barlow, Timothy James January 1986 (has links)
The bulge forming process is a method for shaping tubular components using an internal hydrostatic pressure combined with an axial compressive force. Initial investigations involved carrying out an extensive literature survey to determine the components which could be formed and the types of machines which have been used. Subsequent to this, initial tests were carried out using a previously designed die and tool block in conjunction with a compression testing machine. In these tests copper tubes were formed into expander/reducers and cross pieces by manual adjustment of the axial force and internal pressure. Having obtained experience of the difficulties associated with this die and toolblock, and the loading requirements necessary for theforming process, a new bulge forming machine was designed. The design of the machine was based on the following main criteria: (i) The machine should be free standing and self contained. (ii) The axial deformation of the ends of the tube blank should besynchronised to allow the bulge to form centrally on the tube. (iii) The internal bulge forming pressure should be externallycontrollable during the forming process. (iv) The design should incorporate facilities for subsequent automatic control using a micro-processor/computer. On the basis of these requirements, a machine was designed, built andcommissioned. After correcting a few problems encountered in the commissioning of the machine, a series of tests were carried out, forming tee and cross pieces from copper tube of two different wall thicknesses. These were found to be fairly easy to produce on this new machine. From the resulting components, formed at various combinations of internal pressure and axial compressive force, the limits for a successful forming operation were established. Further analysis of these components was then undertaken to evaluate the effects of the internal pressure and axial compressive force on the bulge height and the wall thickness in the deformation zone. From these results, which have been illustrated graphically, the greatest effect on the resulting bulge can seen to be the axial compressive force. An extension of a theoretical analysis has also been presented, which predicts the wall thickness distribution around the bulge zone. Comparison of these predictions with the experimental wall thickness distributions shows fairly good agreement, especially at the root and tip of the side branch.
49

Development of an electro-hydraulic floating double-disc valve

Usman, Ayo January 1984 (has links)
There is a need for low-cost switching and proportional electro-hydraulic valves with low contamination sensitivity and good reliability. In an attempt to meet this need, a novel electro-hydraulic floating double-disc valve has been developed to the stage where it can be used to control hydraulic cylinders or motors directly. As the valve is significantly underlapped, problems still remain in achieving adequate hydraulic stiffness in the proportional mode of operation. The valve operation, which relies on the complex interaction between fluid and electro-magnetic forces acting on the valve discs, is described and a theoretical model of the fluid and electro-magnetic characteristics of the valve is presented. The theory shows satisfactory agreement with experimental data. A pre-production version of the double-disc valve has been designed and manufactured and it incorporates ideas for manufacturing cost reduction while at the same time conforming to CETOP 3 international valve port standards. This valve has been successfully tested as a switching or proportional device when controlling two different cylinders. Proportional control of the valve is achieved using Pulse-Width-Modulation technique. British Technology Group and University of Surrey have applied for a patent on the valve. The patented floating-disc valve has the following features: (a) 3 way or 4 way 2-position or proportional action with minor changes to produce the two types of action, (b) cartridge construction with interchangeable components, (c) low contamination sensitivity, (d) few critical dimensions, (e) no sliding surfaces, (f) CETOP valve port configuration and (g) potentially capable of operating with corrosive or non-lubricating fluids.
50

A novel technique for tube sinking

Panwher, Mohammad Ibrahim January 1986 (has links)
A new technique for tube sinking has been developed which should, in a number of ways, help to solve the problems associated with conventional tube sinking processes, eg die wear and the need for a swaged down leading end for easy insertion through the die. The conventional reduction die is altogether replaced by a die-less reduction unit of stepped bore configuration. The deformation is induced by means of hydrodynamic pressure and drag force generated in the unit due to the motion of the tube through the viscous fluid medium (polymer melt). The dimensions of the die-less reduction unit are such that the smallest bore size is dimensionally greater than the nominal diameter of the undeformed tube, thus metal to metal contact and hence wear, should no longer be a problem. As no conventional reduction die is used, the need for a reduced diameter leading end is also eliminated. Experimental results show that greater reduction in tube diameter and the coating thickness were obtained at slower drawing speeds (about 0.1 m/s). The maximum reduction in diameter noted was about 7 per cent. Analytical models have been developed, assuming with Newtonian and non-Newtonian characteristics of the pressure medium, which enabled prediction of the length of the deformation zone, percentage reduction in diameter and drawing stress. In the non-Newtonian analysis account was taken of the pressure coefficient of viscosity, derived from the available data; the limiting shear stress, which manifests itself as slip in the polymer melt and the strain hardening and the strain rate sensitivity of the tube material. The percentage reduction in diameter predicted using the Newtonian analyses appear to differ considerably from the experimental results both in trend and magnitude. Non-Newtonian analysis predicted theoretical results which are much closer to the ones observed experimentally.

Page generated in 0.0187 seconds