<p>In the sector of mobile hydraulics, valve controlled systems are predominant. In these systems the load force and speed are adjusted by control valves. In machines where multiple drives are used in parallel at extremely varying loads the energy efficiency of such systems is often compromised over large working regions. Most valve controlled systems also lack the possibility to recuperate potential energy.</p><p>A different category of hydraulic systems, called displacement controlled hydraulics are based on the manipulation of the hydraulic flow using the relative displacement of the hydraulic machines as the final control element. This type of hydrostatic power transfer, yields a resistance free velocity control, ideally leading to lossless load actuation.</p><p>This thesis concerns the introduction of a new type of displacement controlled hydraulic system, adapted for construction machinery. The system decouples the hydraulic functions using one dedicated hydraulic machine for each drive. These machines are of open circuit type, capable of over center operation which enables energy recuperation. The system also comprises four separate valves that by means of switching allow the cylinder to be controlled over all four load quadrants. Depending on the selected valve hardware, the system may also include features available in a conventional valve controlled system, such as meter-out flow control. The system supports both symmetrical and asymmetrical cylinders. However, using the asymmetrical type the load may be controlled in two distinct states of operation. This yields an increased region of operation, which is otherwise generally stated as a drawback in displacement controlled systems. It also allows the selection between different control modes, where one of the modes is always more efficient than another.</p><p>In this research both theoretical studies and a practical implementation demonstrate the energy related benefits of the new concept. The target application of this study is a medium-size wheel loader. Measurement results using the wheel loader in a short truck loading cycle show a 10% percent reduction in fuel consumption. According to the theoretical investigation, this corresponds to a 20% reduction in energy consumption for the hydraulicsystem itself.</p>

Thesis (Ph.D.)--University of Texas at Arlington, 2009.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI Company.

No description available.

This thesis is concerned with the characterisation of the flow behaviour of inelastic and viscoelastic fluids in steady shear and oscillatory shear flows on commercially available rheometers. The first part of this thesis is concerned with a linear viscoelastic theory to describe the oscillatory shear flow behaviour of fluids on a Weissenberg rheogoniometer. A fluid inertia perturbation analysis is used to produce analytical formulae for correcting complex viscosity data for first and second order fluid inertia effects. In order to validate the perturbation theory we perform a simulation of the oscillatory shear flow behaviour of Newtonian and single element Maxwell fluids on a Weissenberg rheogoniometer. A theoretical prediction of end effects and fluid inertia effects on steady shear viscosity measurements of Newtonian fluids in a recessed concentric cylinder geometry is developed for a GSR controlled stress rheometer and a Weissenberg rheogoniometer. The relevant equations are solved using a perturbation analysis which is valid for low Reynolds number flows. From this theory correction formulae are produced to compensate for end effects and second order fluid inertia effects in steady shear flows on these instruments. End effects and fluid inertia effects are also investigated for power law shear thinning fluids. The final part of the thesis is concerned with a theoretical prediction of the end effect of a recessed concentric cylinder geometry on complex viscosity measurements of a generalised linear viscoelastic fluid. The linear viscoelastic theory is carried out for oscillatory shear flows on a CSR controlled stress rheometer and a Weissenberg rheogoniometer. A fluid inertia perturbation analysis is used to produce analytical formulae to correct complex viscosity data for end effects and second order fluid inertia effects. Numerically simulated oscillatory shear data is used to establish the limitations of the second order fluid inertia correction formulae which include end effects.

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In the present research three dimensional, incompressible turbulent jet flows from sharp edged rectangular orifices were numerically simulated. Preliminary studies employing the standard k-E turbulence model stressed the sensitivity of the flow to the specification of turbulence quantities at the inlet. The definition of correct turbulence quantities at the inflow of large eddy simulations was also shown to be crucial for realistic simulations. Consequently, a novel computationally inexpensive boundary condition, that provided turbulence data with known energy, was developed and programmed into a commercial finite element code. The large eddy simulations provided instantaneous data that demonstrated the emergence of complex flow patterns within a short axial distance. The upstream geometry from the jet exit was not included in the present simulations. Therefore, the swirling motion and vortical structures observed could not be related to the different rates of contraction upstream of the discharge plane. In addition, saddle-backed profiles were observed in the long axis of the jet stream. The saddlebacked profiles were formed by a combination of the secondary motions and curvature of the streamlines due to the entrained fluid entering normally to the main jet stream. Turbulence quantities were quantified from the large eddy simulations and showed similar trends to the verifying experimental data. The round jet assumption used in the past to study gas leakage from pipework was found to be invalid in the near field. The simulations clearly illustrate differences between the flow field, the turbulence field, and the coherent structures of a rectangular jet and a round jet. Regions of high and low mixing between the escaping flammable gas and the surrounding air were identified in the large eddy simulations. Furthermore, the coherent structures in the shear layers that resulted in a flapping motion in the lateral direction of the jet, were recognised as important entrainment mechanisms. Numerical techniques have been developed that can be used to investigate gas leakage in detail. The time dependent numerical data provides valuable insight into the mixing mechanisms of the local gas/air mixture thus aiding the safer design of offshore structures.

Three sensor systems measuring particle velocity in gas-solids flows have been studied. These are the microwave Doppler flow sensor, the electrostatic sensor, and the microwave sensor for correlation measurement, all utilizing different principles of operation. The Doppler sensor is based on the Doppler frequency shift observed when microwaves are backscattered by moving targets. An analysis of the process of Doppler signal generation and a computer model based on this analysis have been presented. A novel feature of this work is the implementation of partial screening of the flow field which improves the shape of the Doppler spectrum and results in a mean Doppler frequency proportional to the flow velocity and independent of the flow profile. The electrostatic sensor is based on the principle of monitoring the charge induced on metallic surfaces by charged particles moving in their neighbourhood. A theoretical analysis of the spatial performance of the sensor along with a computer model and experimental verification are presented. Principally, ring type of sensors have been examined and the streched band electrostatic sensor is introduced (SBES). The advantage gained with the introduction of the stretched band electrostatic sensor is a uniform sensitivity across the plane of the sensor. The microwave correlation sensor follows the principles of previous ultrasonic and laser correlation flovrneters. That is, "a transmitted beam penetrates the flow field, suffers modulation, and is detected by receivers placed on the other side of the flow field. An analysis of the principles has been presented and a simplified computer model has been used for system design studies. The study presented here shows that a microwave correlation sensor is viable device for measuring solids velocity. Wherever possible direct comparisons of the properties and the performance of the three sensors are made in order to draw conclusions as to which sensor is best for a specific industrial application. Engineering, environmental and safety problems which might be encountered in the practical implementation of the sensors are discussed. In addition, areas of uncertainty where further work is required are summarized.

This thesis presents the findings from a three year research project into the performance of turbine meters in two-phase flows. The aim was to determine the geometrical changes needed to be made to the rotor design to allow it to register total volumetric flow when subjected to two-phase flows. A single-phase model is presented based on airfoil theory and including retarding torque terms, velocity profile and blade interference effects. Differences of less than 1% between experimental and theoretical results, over the operating range of the meter are shown. The performance of a range of meters in various two-phase flows is discussed. With the exception of the 40 degree rotor in water/air the results may be summarized as follows. At low flow rates, of between 5 and 20 to 30l/s, the meters tend to underestimate total volumetric flow by up to -10% at void fractions of 25%. The greater the void fraction the greater the underestimation. At high liquid flow rates, above 30 to 40l/s, the meters overestimate total volumetric flow rate by as much as 8% at a 25% void fraction. A reasoned arguement is presented to explain the performanceof the meters in two-phase flow. This is based on phase distribution effects, influenced by the varying flow patterns, which alters the magnitude of the driving torque developed radially along each blade. Using this explanation the single-phase model is developed to encompass two-phase flow. Agreement between experimental and theoretical results is good, particularly in that the sense of the meter error is correctly predicted by the model. Quantatively, errors of less than 2% are achieved. From this model, it was apparent that simple geometrica1 changes to the rotors' design were unlikely to bring about the changes in performance needed to meet the original aim of the project. It must therefore be accepted that, in its existing form and using established pulse total ising techniques, the turbine meter is not suitable for use as a two-phase flow measurement device. The author has discovered a relationship between fluctuations in rotor angular velocity and flow void fraction. It is shown that after suitable processing a single characteristic may be used to describe the meters' response to all void fractions up to 25%, the limit of the test facilities. After calibration of the meter, at a single void fraction, it can be used to indicate both void fraction and flow rate directly. Even at this early stage of development, errors of less than 10% are being achieved in indicated void fraction. This technique is covered by a patent, the rights to which are held by the DTI as the funding body.

No description available.