No description available.

No description available.

The objective of the research programme has been to develop design parameters applicable to in-service submarine pipeline buckling behaviour. The programme has involved experimental and theoretical studies and computer graphics are widely employed throughout. Initially, as detailed in Chapter 1, the necessary buckling mechanisms in. pipelines subjected to axial compression have been identified and analysed in the form of relatively basic fully mobilised studies. In addition, errors and limitations contained within these studies have been determined and delineated. Consequently, geotechnical experimentation as reported in Chapter 2 was deemed necessary particularly given the dearth of information available relating to the nature of the friction resistance force between the pipeline and its supporting medium. Full scale values for the axial and lateral friction coefficients together with their respective fully mobilised displacements have been deduced upon the basis of model tests. A semi-empirical formula has thereby been produced for use in design practice. Further, a novel interpretation of sea bed recovery, or the pipeline's submerged self-weight inertial characteristics associated with vertical buckling, has also been determined. Following on from the above geotechnical study,more refined quasi-idealised analyses,dealt with in Chapter 3, have been undertaken incorporating the appropriate full scale deformation-dependent axial and lateral friction-response loci together with the respective sea bed recovery characteristics. These analyses enable, for the first time, definition of the appropriate critical temperature rise at which axial-flexural bifurcation occurs. Finally, noting that previous buckling analyses have been based on quasi-idealised buckling phenomena, attempts have also been made to incorporate practical submarine pipeline imperfections. Pipelines are not perfectly straight in field conditions and, consequently, the imperfection studies denoted in Chapter 4 have attempted to model the appropriate behaviour. Design charts have been produced accordingly and suggestions made regarding further studies.

This work deals with the processes occurring during the firing of an impact-cumulation water cannon. The breakup of the impulsive water jets produced by such a device is explained in terms of the overpressure of the jets on emergence. Design criteria are identified to produce a fast, coherent jet from such a machine. Pressure histories are shown in the nozzle of the water cannon, together with pressures caused by the impact of a fast moving piston on a water packet. Measurements of the forces exerted by the water jets are given, for jets produced with air or with vacuum in the nozzle. A method for finding the jet head velocity decay is introduced, together with results therefrom. A substantial decay in the jet velocity with distance from the nozzle is noted, for the basic design of water cannon. The pressure distribution in lengths of straight tube attached to the end of the converging region of a nozzle is given, and shows a rapid and exponential fall from the high pressure generated in the nozzle. The impulsive blast noise produced by the firing of the water cannon is quantified and is shown to be eliminated when the piston-water impact is cushioned.

The removal of dust from a filter surface usually involves rapid motion which induces a cleaning force at the dust/surface boundary. In traditional long bag filters large amplitude movement is necessary to generate adequate forces and such motion often results in poor cleaning,premature bag wear and filter blinding. The flat geometry inclined filter was conceived to utilise the enhanced movement propogation of planar surfaces and to maximise the use of the available ground area. A detailed theoretical and pracical examination of the operation and cleaning of such filters has shown that the concept and practicality are in close agreement. The research has indicated that the removal of filter cakes involves inducing cake removal forces in excess of the adhesion forces of the cake/membrane combination. For inclined filters the removal of a cake also involves the transportation of material to the edge of the filter surface, hence combining cleaning and discharge. The filter material is not excessively flexed as a pre-requisite of cake removal and hence membrane wear is low. No general optimum frequency or amplitude can be identified for cake removal and transport because vibration characteristics depend on the size and construction of the filter elements. For a particular construction the optimum frequency was found to to be the resonant frequency of the filter element suspension. The removal of cake was shown to depend upon the product of the cake areal mass and acceleration at each point on the filtration surface (cake removal stress). The concept of vibration transmission and cake removal have been used in a computer model in which the cake and filter medium resistances are combined using a series/parallel concept.

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.