Two types of novel electro-hydraulic floating disc type of switching valves have been investigated. Prototype valves of both types have been built and the basic mode of operation confirmed. Due to the complexity of a detailed description of the valve operation, a quasi-steady state computer model has been adopted which has allowed some of the valve characteristics to be adequately described and has given valuable insight into the operation of valves . The single-disc valve, while having the merit of simplicity, was found to have a significant steady power loss when using a 25mm diameter disc size. Due to this, its main application is thought to be as a miniature pilot or first stage valve, as it could be manufactured to less than half the present size. The double-disc valve, while being more complex, has the important advantages of no quiescent power loss and low sensitivity to particle contamination. It is envisaged that the valve could be made in a range of flow capacities, either as a single- or two-stage device with the 2-position, 3-way porting arrangement preferred for remotely controlled micro-processor applications. Steady-state load flow and pressure characteristics are presented and are shown to agree well with the theoretical model. Experimental switching tests on both valves have established that they can be switched continuously at 50Hz, at supply pressures of 100 bar, from nozzle-to-nozzle, but much higher frequencies can be used for pulse-width-modulation where there is no contact between the disc and the nozzle.

No description available.

This thesis investigates two slender body problems, namely the static and dynamic analysis of submarine pipeline spans and the dynamic analysis of marine risers. In view of structural and environmental similarities, these problems are closely related and where possible common analysis procedures have been developed. For the problem of pipe spanning, attention is focused on the possibility of vortex induced vibration and the associated question of span assessment. This situation arises when following the discovery of a span, an assess- ment is required to determine if any remedial repair work required. To assist in this assessment, and also to provide a more fundamental understanding of span behaviour, number of mathematical models are developed. First linear beam-column theory is used to determine the span natural frequencies and buckling load for a single span supported continuously on either side by an elastic foundation. The effects of internal/external pressures and product temperature are included and the results presented terms of two independent nondimensional parameters. Next the effects of pipe/soil friction and change in geometry are considered utilising a nonlinear Finite Element model. Theories are developed for a nonlinear pipe element with axial/bending coupling and a nonlinear nonconservative pipe/soil friction element. The effects of initial seabed geometry and finite amplitude vibration are included and it shown that span frequencies are sensitive to both end friction constraints and seabed geometry. . For marine riser dynamics, an attempt is made to synthesise the best parts from the many and varied analysis methods developed to date, into a simple but flexible design-orientated program. The riser is represented using a Finite Element model similar to that employed for the pipeline spans, and a reduced set of equations obtained using a component mode synthesis method. Several riser/ articulated column designs are considered and the results found to agree with published data.

The research reported in this thesis investigates the nature of trench excavation induced ground movements and their adverse effect on adjacent buried pipelines. The factors affecting the 'in-service' performance of buried pipelines are first reviewed. This is followed by a review of the available field data relating to ground movements induced by trench excavations. A finite element parametric study of trench excavation induced ground movements under undrained conditions is then presented. The models used are governed by linear elasticity. The results indicate that the pattern and magnitude of ground movements are dependent on the soil properties, the excavation geometry and the in-situ stresses. These results show a very rapid build up of movement near the trench ends. The results of a soil-pipe interaction analysis demonstrate high concentrations of bending and shear forces near the trench ends. Analytical studies aiming to assess the interface slippage and the free rotations of the pipe joints show no significant adverse effects. The most important factors affecting the bending moments induced in the pipe are found to be the excavation depth, the soil in-situ stresses, the pipe position, the soil modulus and the relative modulus of the soil and the pipe. An analytical study shows that the provision of rigid supports to the sides of a trench excavated in different stages may result in fixing of the pipe curvature and lead to an overall increase of bending moments. A procedure for estimating the maximum immediate strains in pipes, induced by adjacent trench excavations is finally proposed.

No description available.

Methods and mechanisms of liquid mixing have received only limited research and development, yet mixing is one of the most common operations in the chemical industry. Most of these investigations have been into mechanical devices with few studies being made of other methods.

The development of electrohydraulic floating-disc valves at the University of Surrey started in the early 1980's. The progress in the last ten years since then has shown that floating-disc valves have the advantages of fast response time, reliable operation, simple configurations, few critical dimensions with no precision sliding surfaces, leading to low cost design and manufacture. They have great potential to fill the gap between conventional solenoid valves and high precision servo valves. However, limitations existed in previous designs hindering further development; for instance relatively large moving mass, low hydraulic stiffness, difficulty of installing springs and poor null position when operating in proportional control mode. The work presented in this thesis concentrates on improving the disc valve electromagnetic characteristics, hydraulic stiffness, electric power consumption, operating reliability, valve size and cost. A novel diaphragm-disc force motor has been successfully developed through this research. The theoretical study and experimental work has shown that the force motor has the features of high spring stiffness, fast response, improved accuracy and linearity, and miniaturised size. By implementing a pair of permanent ring magnets, the diaphragm-disc force motor also has the advantages of lower electric power consumption, dual-lane for fail safety operation, and higher control accuracy. Due to the use of conventional mild steel instead of Remco B soft iron as the coil magnetic conductor material, the valve manufacturing cost has been further reduced. Above all, this novel configuration shows good prospects of competing with the existing torque motor due to its low cost and simple construction. The research described also involves designing and testing two prototype disc valves for specific applications. A single disc pilot valve associated with the diaphragm configuration and permanent magnet arrangement has been built for use in an aviation engine fuel supply system. It has a dual-lane operating mode with a valve size of 58x50x50 millimetres, which is the smallest valve yet made in the disc valve family. The initial test results showed that the valve has good linearity and a bandwidth of 60 Hz in a blocked-load condition. Another successfully built valve is an improved version of a position controlled double-disc valve for use in vehicle semi-active suspension systems. It has been demonstrated that using proportional plus derivative electronic network compensation, the valve can operate continually in the whole damper control domain with the characteristics of balanced fluid forces and low electric power consumption.

No description available.

No description available.

No description available.