The main objective of this thesis is to study and investigate the dynamics and stability of cantilevered structures subjected to internal, external, or simultaneous internal and external axial flows. This was accomplished, in some cases, by deriving the linear equations of motion using a Newtonian approach and, in other cases, by making the necessary modifications to existing theoretical models. The continuous cantilevered systems were then discretized using the Galerkin method in order to determine their complex eigenfrequencies. Moreover, numerous experiments were performed to compare and validate, or otherwise, the theoretical models proposed. More specifically, the four cantilevered systems studied were the following: (i) a pipe conveying fluid that is fitted with a stabilizing end-piece, which suppresses flutter by blocking the straight-through exit of flow at the downstream end; (ii) a pipe aspirating fluid, which flutters at low flow velocities in its first mode; (iii) a free-clamped cylinder (i.e. with the upstream end free and the downstream end clamped) in confined axial flow, which also flutters at low flow velocities in its first mode and eventually develops a buckling instability; and (iv) a pipe subjected to internal flow, which after exiting the pipe is transformed to a confined counter-current annular flow, that becomes unstable by flutter too.

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Pipejacking is a tunnel construction technique which is increasing in popularity, but fundamental research is necessary to fully understand the extent of its possible uses and limitations. This dissertation reports on laboratory research into the performance of reinforced concrete pipes, assessment of pipe joints and the use of joint packing materials. The research has addressed specific problems which the tunnelling fraternity have raised. Model pipes have been constructed at scales of 1:6 and 1:10.5 using reinforced microconcrete and they have been tested in either a sand filled chamber or between supporting yokes. Current British Standard tests have been used as a control on the quality of pipe manufacture. Data have been recorded of changes in soil pressures, pipe geometry and strains induced in the pipes. The tests have investigated deformation of pipes, deflection angles between consecutive pipes, distribution of stress concentrations and the effects of the use of joint packing materials on allowable jacking loads and induced stress magnitudes in the pipes. A review of current pipejacking practice is presented and recommendations for the control and supervision of pipejacking operations are made. The conclusions include recommendations for fieldwork monitoring and implications of this stage of the research to industry. Recommendations are made for maximum installation jacking loads for any given deflection angle between pipes. The prediction of friction angles at the pipe soil interface have been assessed at different soil stress levels and new recommendations are made. The effects of cyclic loading on the pipejacking system and transfer from jacking load to ground loading once the pipes are installed are presented. The criteria used in the selection of a recommended joint packing material for use in jacking operations have been included. Failure modes of pipes are stated and recommendations are made for pipe design, installation and monitoring to predict and prevent such failures. This dissertation is the report on the first stage of an overall programme of research which is now set to progress with monitoring of pipejacking operations on several construction sites.

The development of a fuel filler pipe is based solely on experience and physical experiment. The challenge lies in designing the pipe to fulfill the customer needs. In other words designing the pipe such as the fuel flow does not splash back on the fuel dispenser causing a premature shut off. To improve this “trial-and-error” based development a computational fluid dynamics (CFD) model of the refueling process is investigated. In this thesis a CFD model has been developed that can predict the fuel flow in the filler pipe. Worst case scenario of the refueling process is during the first second when the tank is partially filled. The most critical fluid is diesel due to the commercially high volume flow of 55 l/min. Due to limitations of computational resources the simulations are focused on the first second of the refueling process. The challenge in this project is creating a CFD model that is time efficient, thus require the least amount of computational resources necessary to provide useful information. A multiphase model is required to simulate the refueling process. In this project the implicit volume of fluid (VOF) has been used which has previously proven to be a suitable choice for refueling simulations. The project is divided into two parts. Part one starts with experiments and simulations of a simplified fuel system with water as acting liquid with a Reynolds number of 90 000. A short comparison between three different turbulence models has been investigated (LES, DES and URANS) where the most promising turbulence model is URANS, specifically the SST k-ω model. A sensitivity analysis was performed on the chosen turbulence model. Between the chosen mesh and the densest mesh the difference of streamwise velocity in the boundary layer was 2.6 %. The chosen mesh with 1.9 M cells and a time step of 1e-4 s was found to be the best correlating model with respect to the experiments. In part two a real fuel filling system was investigated both with experiments and simulations with the same computational model as the chosen one from part one. The change of fluid and geometry resulted in a lower Reynolds number of 12 000. Two different versions of the fuel system was investigated; with a bypass pipe and without a bypass pipe. Because of a larger volumetric region the resulting mesh had 3.7 M cells. The finished model takes about 230 h on a local workstation with 11 cores. On a cluster with 200 cores the same simulation takes 30 h. The resulting model suffered from interpolation errors at the inlet which resulted in a volume flow of 50 l/min as opposed to 55 l/min in the experiments. Despite the difference the model could capture the key flow characteristics. With the developed model a new filler pipe can be easily implemented and provide results in shorter time than a prototype filler pipe can be ordered. This will increase the chances of ordering one single prototype that fulfills all requirements. While the simulation model cannot completely replace verification by experiments it provides information that transforms the development of the filler pipe to knowledge based development.

The majority of commercially available ultrasonic transducers used to excite and measure wave propagation in structures can be coupled only to a free surface. While convenient, this method is likely to excite multiple structural modes, making data interpretation difficult. Furthermore, the many modes excited make predicting the structure’s response a computationally intensive task. Here the dynamic radial displacement induced by a transient radial point load is calculated at more than 230,000 points on the outer surface of a virgin steel pipe to simulate a typical experiment. The radial component of the displacement field is calculated by convolving the Green’s functions of the pipe with the transient load. These functions are calculated on personal computers (in a distributed arrangement) by employing modal summation. The mode shapes are obtained from a Semi-Analytical Finite Element formulation used in conjunction with a separation of variables. The results are presented in a four dimensional animation, providing easier interpretations and insight into how to best select observation points for the detection of defects. The accuracy of the calculated displacements is verified experimentally. Agreement is good when magnitude and phase corrections are incorporated from the frequency response curves of the transducers used.

The purpose of the work described here is to analyse vortex induced vibration VIV) effects on marine risers and unorthodox forms of suppression of this phe¬nomenon. which can cause structural failure through metal fatigue. Two suppression methods are explored: flex joints and buoyancy modules. Flex joints. which act like a hinge at a point on the riser due to the large reduction in bending stiffness. can suppress higher modes of vibration from propagating along or appearing in the riser. Buoyancy modules, with their local 100% increase in riser diameter. can decorrelate vortex shedding along the span of the riser and reduce the resonant effect of VIV. The numerical finite element cable model and rigid body model developed at the University of Victoria were modified and used as a foundation for the research. The modifications include an algorithm to estimate the forces clue to ocean surface interaction with rigid bodies and a model to produce the appropriate VIV response in the numerical cable model. The resulting VIV model was calibrated and validated with analytical. experimental, and numerical data available in the literature. In general. the model produces qualitative effects of VIV. including its self-starting and self-limiting nature, frequency lock-in. multi-mode response. and limited structural response on the order of one diameter. A simulation of a testbed riser in a variety of ocean currents was generated to observe the effects of installing flex joints and buoyancy modules at various locations along the riser span. The performance of the testbed riser was gauged by comparing the time series of von Mises stress and the associated safety factor, ns. from fatigue failure at many points along the span to an unmodified testbed riser. The stress fluctuation was drastically reduced within the flex joints for all water currents studied, which greatly increases fatigue performance. Flex joints placed at the top of the testbed riser had less impact. as the stresses are dominated by the large and unavoidable tensions found there. Flex joints placed in the bottom region of the riser did not affect the ns,. of the remaining riser span until very high modes of vibration were present. At these higher modes. some testbed riser configurations changed their vibration envelope and frequency. which indicates that a possible alternate and less damaging mode of vibration was induced. Flex joints therefore act effectively as a local patch against poor fatigue performance and placement of several flex joints does not negatively impact the behaviour of the rest of the riser in the cases examined. However. the explicit relationship between placement and spacing of flex joints with environment conditions remains unknown. Buoyancy modules introduced spatial fluctuations in the entire nu profile of the testbed riser, unlike flex joints. In addition. the buoyancy modules decreased n, performance due to the hydrodynamic load concentrations induced by their large diameters. However, the 16% coverage case increased n.,. elsewhere along the riser, though the 10% covered riser did not match this performance. Since in both cases the modules were evenly spaced along the riser. performance benefits from increased coverage implies a minimum coverage of 16% needed for significant improvement in fatigue performance for devices of this type. This coverage requirement may apply to traditional VIV suppression devices such as helical strokes. since they decorrelate vortex shedding along the span of the riser albeit in a different manner than buoyancy modules. Finally. the buoyancy modules changed the stress oscillation frequency more than the flex joint cases from the unmodified riser. This is desirable since lowering the frequency of oscillation also increases the fatigue performance of the riser.

While much money and effort has been spent by manufacturers and users of pipe jacking equipment to develop suitable techniques, this work appears to be the first to study the method at full scale, in a scientific research programme. It has involved monitoring a series of five pipe jacks during construction. In each case a heavily instrumented pipe was incorporated into the pipe string to measure pipe joint stresses, pipe and joint compressions and contact stresses between pipe and ground. Total jacking loads and movements of the pipe string were also measured and all results correlated with a detailed site log, full tunnel alignment surveys, and observed ground conditions. The success of the site monitoring has been highly dependent upon the development of a suitable instrumentation and data acquisition system in conjunction with appropriate site procedures for working in the restricted and physically demanding pipe jack environment without undue disruption to normal site operations. The build up of total jacking force is the result of highly complex soil-pipe interaction. The local interface stresses are essentially frictional in most ground conditions, and can be related to the shear strength of the ground. The problem is in determining the effective radial stresses which are affected by soil insitu stresses, stiffness and strength; groundwater conditions; rate of progress; pipeline misalignment and use of lubricants. Relations between pressure distributions at pipe joints and measured tunnel alignments are presented. That small angular deviations between successive pipes cause severe localisation of stresses on their ends is clearly demonstrated. Careful back analysis shows that the linear stress approach of the Concrete Pipe Association of Australia can adequately match the measured stresses and could be used by pipe manufacturers to provide design data on allowable jacking forces for pipes on the basis of pipe size, packer properties, concrete strength and angular alignment. It is also clear from the small pipe barrel stresses that improved packing materials would allow more of the potential strength of pipes to be achieved. Since relative angular than absolute deviations control transfer mechanisms between pipes, uncritical adherence to specifications based on absolute line and level is counter-productive.

Pipe jacking is a trenchless construction technique for the installation of underground pipelines. Although pipe jacking is widely used, fundamental research is still needed to understand fully the factors affecting the process and to prevent unexpected failure. With the time and financial limitation, it is difficult to explore all aspects of these factors with experiments; and it is also difficult to study them by analytical methods because of the complexity of the problem. This thesis describes the use of the finite element technique to study the pipe performance under different environments and the laboratory tests of several different joint designs. The emphasis of the current research is on the performance of the concrete pipes during jacking under working conditions and to seek possible improvements in the design of pipes and pipe joints by numerical modelling. In the finite element modelling, a simplified two-dimensional model is used for a preliminary study, then the analyses are carried out with three-dimensional models A, B and C representing a complete pipe, a pipe with surrounding soil and a symmetric three-pipe system respectively. Several factors affecting the pipe performance have been examined, for example, the properties of the packing material, the stiffness of the surrounding soil, the misalignment angle at the pipe joint, and the interaction between the pipe and surrounding soil. The numerical results show that the misalignment of the pipe is the dominating factor inducing both tensile stresses and localized compressive stresses in the concrete pipe, especially with a high misalignment angle which results in separation between packing material and the pipe. The packing materials with high Poisson's ratio and high stiffness also induce higher tensile stresses in the pipe, and the influence of Poisson's ratio is significant. Under 'diagonal' loading, both the stiffness of the surrounding soil and the interaction between the pipe and the surrounding soil have a significant effect on the stresses within the concrete pipe. Under 'edge' loading, the greatest potential damage is at the pipe joint due to the tensile stresses in the hoop direction; while under 'diagonal' loading, the damage is most likely the cracking on the external surface of the pipe along a line connecting the two diagonal loaded corners. The results show that the Australian model gives somewhat good prediction about the maximum normal stress and the diametrical contact width at pipe joint. Based on the numerical results, several different joint designs for improving the pipe strength have been proposed and tested in the laboratory. Both the laboratory tests and the back analyses suggest that the local reinforcement and the local prestressed band at the pipe joint will improve the pipe strength.

The reported work constituted the third phase of a programme of research into the performance of concrete pipes during installation by the pipe-jacked tunnelling technique. This third stage was a continuation of the on-site monitoring of full-scale pipe jacks during construction. Four schemes were monitored in different ground conditions: London clay, dense fine sand below the water table, stiff glacial till and soft alluvial clay. Pipe sizes ranged from 1000mm to 1800mm internal diameter and excavation methods included hand tools, slurry machines and an open face tunnel boring machine. The main objective was to collect information on jacking loads and stresses at the pipe-soil interface to provide a better basis for future designs. This was achieved by building twelve stress cells -capable of measuring total normal stresses, shear stresses and pore pressures - into the wall of a standard concrete jacking pipe that could be inserted anywhere in the pipe string. Jacking loads and forward movement of the pipe string were simultaneously recorded and the results were correlated against site activities, including lubrication operations, and tunnel alignment surveys. Another objective was to monitor the ground response by measuring displacements around the tunnel and ground pressures above the perpendicular to the intended line. Ground movements were measured using conventional surveying techniques for surface settlements, and inclinometer access tubes for sub-surface deformation. On one scheme, electro-levels were employed in a near-horizontal tube to measure centre line settlement as the tunnel bore advanced. Push-in spade cells and pneumatic piezometers were installed on two schemes to measure the change in horizontal pressures with the passage of the shield. Because of the myriad data collected, it has only been possible to present a summary of the results obtained. Jacking force records from all the monitored schemes - including the previous fieldwork stage - are presented. The pattern of jacking load build up and the magnitude of frictional resistance can differ significantly according to the type of ground and use of lubricants. Stress measurements at the pipe-soil interface show that the interaction between jacking loads, pipeline misalignment, stoppages, lubrication, excavation technique etc, is highly complex. Ground movement measurements compared to well established empirical predictive methods show that short-term displacements are related to ground losses caused by closure of the overbreak void between shield and pipe.

The flow of solid liquid mixtures (slurries) has attracted much attention in research work because of its importance to industry. Prediction of pressure losses associated with slurry flow helps pipe designers select the correct pipe sizes for optimum energy consumption, equipment sizing and reliable operation of the pipeline networks. Many workers developed empirical correlations, but due to the randomness of the problem they seem of limited use in design applications because they do not contain an assessment except by trial and error, which is costly. The existence of more than one particle size poses more complexities to the slurry flow problem but it is in need in practical applications. The aims of this work are justified under the light of the observations on the state of the art in slurry transport. An experimental program is designed to highlight the effects of this problem through a predetermined set of test runs. The variables are grouped to optimise the number of experiments and to remove the effect of dimensions on the prediction method The test rig is built to serve the aims of this exercise and test runs conducted, results grouped and discussed for polyfractional slurries. A mathematical model is developed in the form of an empirical correlation. Statistical tests are employed to verify the goodness of fit. Finally, conclusions and recommendations for further work are listed.