The overall aim of this study is to propose and develop a cost effective production design concept suitable for oil reservoirs situated in deep (1500 m) water which can be quickly and safely installed in areas with limited weather windows. The proposed design is based upon a steel catenary riser which will connect an FPSO directly into either a wellhead or seabed pipeline system thereby eliminating both the connection complexes and high cost associated with a central manifold. The catenary geometry will ensure that the structure is inherently compliant whilst a carrier pipe arrangement will provide structural protection and buoyancy to a flowline bundle contained within. The interface between the riser and the surface production vessel is a critical part of any riser system and so for the purposes of this study two design arrangements are considered. The first is based upon a direct connection between an FPSO turret and riser whereas the second is a hybrid design in which the riser is supported by a sub-surface buoy which is hydraulically connected to an FPSO using flexible flowlines. This hybrid connection has the advantage of decoupling FPSO and riser motions. Design development is carried out by examining a range of critical areas.

The optimisation of Sliding Mode controllers for marine vehicle guidance is presented in this thesis. This study is concerned with two optimisation methods which are based on natural processes. The first is Simulated Annealing which involves processes analogous to those involved in the cooling process in metallurgy. The second involves Genetic Algorithms which are based on the evolutionary process of species and genetics. These methods are evaluated through studying their application to the optimisation of controller parameters for particular marine vessels. Their performance is measured through simulation studies during the optimisation process. Existing literature in the fields of the two optimisation techniques, Sliding Mode control and marine control is surveyed. The theory of Simulated Annealing is presented in terms of the optimisation process and its convergence properties through Markov Chain analysis. A novel variation of this method, Segmented Simulated Annealing, is also outlined and evaluated in terms of its improved convergence properties. The theory of Genetic Algorithms is presented in terms of its process and convergence properties using Markov Chains and the Schema Theorem. The derivation of a decoupled Sliding Mode control theory is described and its well known stability robust properties are ensured by the choice of an appropriate set of design criteria. The elimination of the chattering phenomenon is achieved by soft switching which ensures performance robustness. The application of Sliding Mode controllers for governing the motion of three marine vehicles and their subsequent optimisation is presented. The first is the simulation of a linear mathematical representation of a military submarine. The second is the simulation of a non-linear mathematical representation of a super tanker. The third is an actual scale model of a supply ship which enables evaluation of the optimised controllers in a laboratory water basin facility.

Buoyancy control is needed in small autonomous underwater devices to enable greater flexibility in measurements in the ocean. This project has examined a number of ways in which buoyancy changes might be achieved. Firstly, an extensive review of the mechanisms by which various marine organisms control their buoyancy was undertaken. There is a tremendous diversity of natural buoyancy control mechanisms, but most of these mechanisms produce only slow (and small) changes in buoyancy. Studies were carried out on the behaviour of polymer gel systems that exhibit large volume changes under the influence of solvent composition and/or temperature. The effects of salinity were investigated, from 5 parts per thousand (ppt) to 35ppt, on hydrolysed polyacrylamide gels, over the temperature range of 5°C to 40°C. It was found that the gels decreased in volume in the solutions, this effect being most pronounced in the 35ppt solution. As temperature increased, the volume changes were observed to decrease. The cyclical volumetric strain behaviour of the polyacrylamide gels, by alternate exposure to saline solutions and distilled water, resulted in significant (~200%) volume changes induced over periods of 2 days. In a second study, the density change associated with the volumetric strain of polymeric materials was investigated in poly(N-isopropylacrylamide), NIPA, gels. The temperature-sensitive NIPA gels, immersed in distilled water or seawater solutions at temperatures ranging from 5°C to 50°C, exhibited volume changes of over 800%, and density changes of 30-40%. NIPA gels exhibit a faster response time than polyacrylamide gels, and their density and volume changes have potential application in buoyancy change. Experiments were also performed on NiTi shape memory alloys (SMA), which change in length and mechanical properties with temperature. A controllable parallel-plate device was constructed, linked by four helical SMA springs, which exerted significant axial forces with the application of temperature. The device is capable of producing substantial volume changes if contained in a suitable enclosure. It is currently on loan to the Science Museum, London, as part of a new exhibition of the Wellcome Wing.

This thesis presents theoretical formulations and numerical computations for predicting first- and second-order hydrodynamic forces on a marine vehicle advancing in waves. The theoretical formulation starts with the derivation of the governing equations for the boundary-value problem of potential flow and its consequence leads to linearised radiation and diffraction problems using the peturbation expansion technique. Solutions of these two problems are obtained by solving the three-dimensional Green function integral equations over the mean wetted body surface. The forward speed free surface Green function representing a translating pulsating source potential for infinite water depth and finite water depth is derived using double Fourier transformation technique. This source potential reduces to an oscillating source at zero speed or to a Kelvin source at zero frequency. In order to solve the three-dimensional Green function integral equations efficiently, symmetry properties of the Green function and the body surface are exploited in the numerical implementation. Using a fully submerged ellipsoid and a half-submerged ellipsoid as examples, the free surface and forward speed effects on hydrodynamic coefficients are investigated. Their cross coupled hydrodynamic coefficients calculated by the present theory satisfy with Timman-Newman relationships. Numerical results for the first-order hydrodynamic coefficients, the wave excitation loads and the resulting motion responses of surface ships are presented. For zero speed case excellent correlations between the calculated and experimental results are found. For the forward speed case, the three-dimensional translating pulsating source modelling and three-dimensional oscillating source modelling with simple speed corrections on the linearised body boundary condition for pitch and yaw motions are used for a realistic ship. When the calculated results are compared with available experimental data, the three-dimensional translating pulsating source, modelling gives better correlations than the three-dimensional oscillating source modelling. Based on the first-order solutions, the mean second-order forces and moments are obtained by direct integrating second-order pressures over the mean wetted body surface. Using zero speed horizontal drifting forces and mean yaw moment as examples, the predictions of the mean second-order forces and moments are compared with available experimental results and found good agreement. For forward speed case the numerical computations for the added resistances of surface ships in head waves are performed by the three-dimensional translating pulsating source modelling and three-dimensional oscillating source modelling. The performance of the former is much better than the latter in comparison with available experimental results. It is found that the successful prediction of the peak of the added resistance is critically dependent upon the motion response results, especially in pitch. Effects of ship heading, forward speed, water depth on the first-order and second-order hydrodynamic forces are investigated.

Dam removal has recently emerged as a growing trend in river rehabilitation in the United States. The rate of dam removal has been increasing rapidly since 2000, but is doing so with large gaps in our understanding of how the fluvial system will respond to this disturbance. Most of the structures removed to date have been relatively small and, in the vast majority of cases, have not received any pre- or post-removal monitoring. Very few large structures have been removed but, when such removals occur or are proposed, they tend to attract more monitoring activity because of the generally larger volumes of water and sediment involved. It is thus important to understand the form-process-response interactions that occur during the removal of large dams and the extent to which these may be applicable to other removals of varying sizes. The proposed removal of the Glines Canyon Dam from the Elwha River in Washington, USA provides such an opportunity. The 67-m high dam is due to be incrementally removed in 2011 but its reservoir, Lake Mills, contains 80 years-worth of uncontaminated sediment that has the potential to adversely impact the aquatic and human environment once released into the channel downstream from the dam. In order to better understand the dynamics that control how sediment might be transported into the downstream channel, a series of scaled physical model experiments was performed in which the principle variable investigated was the magnitude of the drop in reservoir water surface elevation. Four main findings emerged from the research. First, the hypothesised relationship between increasing magnitudes of baselevel drop and increasing delta erosion volumes is only weakly developed. Furthermore, the small increases in additional erosion volume for very large increases in magnitude of drop suggest that there may be an upper limit beyond which the volume of sediment eroded does not increase substantially, irrespective of the magnitude of drop. The reasons for this are explored. Second, the volume of delta sediment eroded was greatly affected by the channel’s position on the delta surface at the start of each experimental run. The erosion volumes were greatly modulated when the channel was close to the basin boundary (marginal runs), because the boundary inhibited lateral channel movements and the formation of meander bends. When the channel ran through the middle of the delta surface (central runs) the erosion volumes were much larger, because meander bends were able to more fully develop and the channel had a greater overall freedom to adjust laterally over the entire delta surface. In contrast, the marginal runs generally incised slightly more along the full length of the delta than the central runs, despite a more extensively developed armour layer. Related to the channel’s starting position, a strong element of topographical steering of the incising channel in the original delta area was observed during the marginal runs. When the channels started close to the left basin boundary (left marginal runs), the left hand curvature of this boundary tended to direct the majority of the flow’s erosive power away from the main body of the delta. In contrast, during the right marginal runs, the cross-basin downwards slope from basin right to basin left allowed the incising channel to move downslope and into the main body of the delta, particularly during the post-dam removal flood flows. Third, the armour layer in the central runs generally extended less far downstream through the original delta area than during the marginal runs and this may be because of a frequently observed mobility reversal in sediment transport, which meant that gravels were more effectively flushed out of the original delta area than during the marginal runs. Finally, a phenomenon hitherto unreported in the literature was observed on many occasions over the course of the experimental runs. Bed Elevation Lowering Without Armour Layer Break-up (BELWALB) occurred when the finer sub-armour sediment was eroded, thus undermining the armour layer and allowing the coarser grains to roll forward by a distance equivalent to a few grain diameters. This undermining action was able to migrate a certain distance upstream, either at the onset or end point of more extensive armour layer disturbance, thus causing subtle changes to bed morphology which are important in understanding how the system approached thresholds of stability and how it responded once these thresholds were exceeded.

The purpose of the labyrinth weir is to increase the discharge per unit length of structure normally obtained from a conventional weir when operating under identical head conditions. This is achieved by compressing a large length of crest in concertina form, into the space available on site. The investigation carried out as described in this thesis aimed to provide comprehensive performance data covering all aspects of labyrinth weir behaviour. This has been achieved by a series of experimental model tests. The initial experimental work was confined to basic labyrinth weir configurations and the significance of the parameters of fundamental importance has been determined. This allowed the definition of the most useful ranges of weir design and subsequent experimental tests were confined to within these ranges. Following the initial experimental work tests were conducted to determine the significance of all the parameters of secondary importance including various refinements to the weir designs such as sloping channel inverts and alternative crest sections etc. A comprehensive set of experimental performance data covering all aspects of labyrinth weir design and behaviour are thus contained in the thesis. A mathematical model representing the behaviour of the weirs has been constructed and translated into a computer programme. Close correlation has been achieved between the theoretical and experimental results and the programme will accurately predict the performance of any labyrinth weir subject to some minor restrictions. The computer programme is included in the thesis so that it will be available to anyone wishing to use it. A design method using two design charts has been developed. This enables the design and performance prediction of any weir designed in accordance with recommendations contained in the thesis. The design charts are included in the text together with a worked example illustrating their use.

The sorting and transport of different sediment fractions and the resulting beachface evolution over the swash zone of a beach, is numerically investigated within the framework of the shallow water theory and the active layer theory. The shallow water and Exner equations, along with the volume fraction (sorting) equation given by the active layer theory compose the system which is numerically solved using an uncoupled approach, i.e., the model assumes that changes in bed level (and volume fraction) do not have an effect on the flow. Two different numerical methods are applied to solve the system depending on the type of flow tested (constant current or swash flow); a classic Finite Differences Method and a hybrid Finite Difference-Method of Characteristics (FD-MOC) are then used respectively. The numerical model is first tested for the case of a sand dune composed of two different sediment fractions subjected to a constant current. Comparison between simulations from the model and results given by Hudson (2001) solution (which only considers one sediment fraction) showed that the composition of the bed is crucial for the subsequent bed evolution. This case served to verify that the equations were solved correctly and some interesting features of the kinematics of the system were observed. The model is then applied to the case in which a single Shen and Meyer (1963b) swash event acts over a plane sloping beach composed of two different sediment fractions in the same proportion. Different values of the A (sediment mobility parameter) are investigated taking as a base point the value calculated by Kelly (2009). The results show that the behaviour in time of Pfa (fine volume fraction in the active layer) directly depends on the difference between sediment mobility parameters (Af and Ac) for the fine and coarse fractions; and this in turn results in an effect on the beachface evolution. The finer the mixture of sediments involved the bigger the bed change. Similar behaviour is obtained when the model is tested for the case in which a non-breaking wave swash is acting over the beach profile, although some interesting differences are noted mainly due to the different driving hydrodynamics.Finally, realistic A parameters for the fine and coarse fraction are defined linking grain diameters that can be found on real beaches to the sediment parameters used in the model.Numerical tests for both type of swash flows (breaking and non-breaking wave) are implemented, in which different initial Pfa distributions are considered. The results from these simulations confirmed the crucial role played by the initial distribution of sediments on the beach evolution; it was observed that a kink in the bed (a sort of swash bar/trough) formed around the middle part of the swash zone for the cases in which the initial distribution of sediments showed a maximum or minimum in that area. Comparing the results given by the model when two sediment fractions are considered, with those when a mean value (A¯ = (Af+Ac) / 2 )which is a common practice in coastal engineering models) showed that the inclusion of the two sediment fractions is crucial in order to get better predictions.

Prediction of conveyance capacity in open channel flows is complex and requires adequate modelling of flow features such as secondary circulation cells and, specifically for over-bank channels, the momentum exchange that occurs at the main channel/floodplain interface. A variety of conveyance estimation methods have been developed with the objective of accurately capturing these flow characteristics through a simplified user-friendly approach. However, these methods usually require calibration of one or more empirical constants. Within this thesis in-bank and over-bank channels have been numerically simulated using Large Eddy Simulation (LES) in order to predict accurate open channel flow behaviour. The LES results are validated against experimental data and then utilised to advise on values of calibration constants f, λ and Γ within a conveyance estimation method, the Shiono and Knight Method (SKM), which has recently been adopted by the Environment Agency (EA) for England and Wales as part of its new Conveyance Estimation System (CES). The LES results are shown to accurately predict the flow features, specifically the distribution of secondary circulations in in-bank channels of aspect ratio as large as 40 and for over-bank channels at varying depth and width ratios. The LES derived f, λ and Γ values are then utilized in the analytical solution of the SKM in order to compute depth averaged velocity profiles for comparison to LES results, producing very good agreement with simulated and experimental profiles. As well as the derivation the calibration constants, the apparent shear stress at the main channel/floodplain interface is investigated and the contributions from both Reynolds stress and secondary circulation terms compared. Also, instantaneous velocity data available from monitor points at the main channel/floodplain interface within over-bank channel simulations is utilized to investigate wave periods of interfacial vortices through spectral analysis. Comparable result to available experimental and stability analysis data are obtained.

The study of open channel flow and dam breaking is not a new topic in computational fluid dynamics. However it has only recently started to gain significant attention from researchers using meshless methods, i.e. numerical modelling techniques which do not rely on the use of a mesh to discretise the domain. The research presented here is an attempt to use the meshless method known as smoothed particle hydrodynamics (SPH) to simulate the flow of water down a channel. Hydra, a pre-existing SPH code designed originally for astrophysical simulations, was converted to simulate water flow and then applied to the problem of dam bursting and flow over a weir. The conversion of the code to its new purpose was verified by simple code tests and then extensive validation was performed via the modelling of multiple dambreaks. The validation process can be split into three broad categories: 1) Comparison against the published data gained from other numerical methods both meshless and traditional. 2) Comparison against physical experiments performed by the author. 3) Comparison against independent experimental data found in the literature. Hydra in its newly converted form was satisfactorily applied to the majority of the tests presented to it and the same level of accuracy was achieved as with any of the other codes tested. A limit to the SPH method for performing this type of simulation was proposed based on particle number, smoothing length and initial conditions. A formula for the calculation of the number of ghost particles required to prevent spurious boundary pressures was also proposed. An analysis of various kernels used by different SPH researchers was presented and it was discovered that a relatively simple cubic spline kernel proved sufficient and that increasing complexity did not provide an increase in solution accuracy. The flow of water over a weir was presented next and results compared to published data which utilised a leading mesh based fluid simulation package. Results gained from Hydra simulations showed good downstream water level prediction but overestimation of upstream levels. A steady state solution was achieved within a similar timeframe compared to the grid based method. It was concluded that use of the SPH method and the Hydra code in particular can provide solutions to problems involving water flow down a channel and accuracy on the dambreak tests was equal to any rival codes/methods tested. However when the complexity of the boundaries involved in the model increased there was some evidence that the CFX simulation package could be used to achieve a more accurate solution than Hydra. Suggestions for continuation of research into Hydra as a water flow modelling code are presented in addition to recommendations for improving the experimental methods used.

Beach cusps are swash zone morphological patterns that have been of interest to many scientists and engineers. This study aims to improve understanding of the formation and long-term evolution of beach cusps by numerical simulation using a 2D process-based morphodynamic model, solving the coupled NLSW equations and sediment conservation equation simultaneously. A numerical implementation is applied building on the model of Dodd et al. (2008), which succeeds in simulating the occurrence of beach cusps. The numerical scheme improves the accuracy and stability of the swash zone computation. Results from a comparison between different numerical implementations concludes that the most suitable numerical scheme is the Roe-averaged scheme of Castro Diaz et al. (2008) with Minmod flux-limiter using the Harten and Hyman (1983) entropy fix method and the Hubbard and Dodd (2002) approach for the shoreline boundary condition. Before simulating the 2D beach cusps, the sensitivity of the model parameters and two different types of incoming waves are tested in the ID bed change. The sensitivity test results show that there is a convergence of the results when the minimum computational depth (dtol) ≤ 1 mm. Also the relationship between the bed profile and beach cusp parameters is that a greater maximum tip position (xs,max) is achieved, and more erosion in the tip region occurs when the bed friction coefficient (ƒw), the hydraulic conductivity (K), and dtol are smaller. On the other hand, the effect of scaling the sediment transport coefficient (A) is to scale the rate of change of the bed level, and appears not to lead to qualitative differences. Moreover, the incoming sine wave creates three components of 1D beach profile (long-shore bar, trough, and swash berm) in the computational domain, while the incoming sawtooth wave creates a wider equivalent region, because of wave simply breaking farther offshore. The 2D simulations give approximately the same beach cusp formation as those of Dodd et al. (2008); however, the geometrical parameters (ƒ) from the self-organisation theory are still high when compared with previous field observation and numerical simulations. The evolution of the beach cusps is investigated by Fourier and global analyses (Garnier et al., 2006), and can be divided into three stages: 1D development in the cross-shore profile, 2D small cusp spacing pattern, and 2D final bigger cusp spacing pattern, caused by the coalescing of two small bays and subsequent rearrangement to an equal spacing. However, an unphysical behaviour is found during cusp evolution, which is the reversing behaviour between horn and embayment. It appears that this reversible behaviour is caused by deposition at the embayment head, created from high infiltration and the usage of the velocity-only type of sediment transport equation in the model.