The UK is facing an energy crisis due to the closure of old nuclear power plants which will not be replaced until Generation III nuclear reactors are built. Coal is a realistic option to fill the gap, although there is a need to use cleaner and efficient technologies as a means to comply with global environmental regulations. Supercritical coal-fired power is a viable clean coal technology; however the UK National Grid Code is built around conventional power plants, and thus compliance is uncertain. Modelling the thermal behaviour of the supercritical boiler water cycle using computational fluid dynamics is a practical method to approach compliance. The CFD models developed with the software Comsol Multiphysics were validated and verified using experimental and numerical data, respectively. Subsequently, a test-element representing one pipe from the water wall was scaled-down to match computational requirements, and tested at two different thermal boundary conditions. A strong, forcedconvective flow was revealed, with buoyancy effects at the inlet and a considerable influence of thermal acceleration. The sharp changes of the thermo-physical properties were the most influential hydrothermal factor. Heat transfer coefficient peaked near the pipe inlet, and the outlet section showed mild hydro-thermal performance, impaired by the acceleration effects.

Maximum equilibrium scour depths, equilibrium scour volumes, and induced equilibrium movements at isolated obstacles on river beds were investigated in clear-water scour. The research was achieved by a systematic flume study based on the results of dimensional analysis of local scour. The main tested obstacles for local scour were cubes. Local scour at a circular cylinder of aspect ratio 1 and a sphere were also examined for comparison with scour at cubes. Each obstacle was placed on a flat movable bed and oriented normal to the incident flow. Non-cohesive uniform medium sand and very fine gravel were used as movable beds. The tested flow conditions were controlled to give many combinations of the relevant dimensionless parameters for local scour: the flow Froude Number, relative obstacle size, and relative roughness of bed material. Water surface profiles and longitudinal velocity profiles along the plane of symmetry, as well as the horizontal velocities near the bed around isolated obstacles on a fixed bed were examined in several runs. For a slightly submerged cube, the path of maximum velocity downstream of the cube moves from the water surface into the lower part of the flow. At a greater distance downstream, the path of maximum velocity tends to move upward toward the water surface. An increase of flow Froude Number leads to a hydraulic jump behind the cube. The relative longitudinal velocity near the bed is increased in this region. The decrease of relative water depth or the increase of flow Froude Number can lead to increased average relative horizontal velocity (V/u) near a cube. The cube has the highest average V/u value, as compared to flow near a circular cylinder and a sphere. The local scour processes and equilibrium scour patterns at isolated cubes on movable beds were also examined. There is not a unique equilibrium scour pattern for clear-water scour at a cube on a movable bed. Equations were developed to predict the maximum equilibrium scour depth and scour volume and the critical condition for incipient motion of bed material at a cube in clear-water scour. As the water becomes relatively deep, the shape effect of the circular cylinder and the sphere become negligible. The major equilibrium movement of a cube on a movable bed due to scour involves longitudinal displacement, vertical settlement, and longitudinal inclination. Equations were developed to predict the equilibrium movement and the critical condition for incipient upstream movement of a cube in clear-water scour. / Graduation date: 1991

Dissertation (Ph.D.)--University of Toledo, 2009. / Typescript. "Submitted as partial fulfillment of the requirements for the Doctor of Philosophy degree in Mechanical Engineering." Bibliography: leaves 203-209.

Thesis (M. Phil.)--University of Hong Kong, 1982.

An understanding of the interaction between flow, sediment and bed morphology is essential for dealing with engineering problems such as floods, river bank erosion and sedimentation in reservoirs. However, the morphodynamic processes in natural braided rivers are still not well understood due to difficulties in measurements in field. Numerical models provide a considerable assistance to investigate these complicated processes in natural rivers. In the present study, a physics-based two-dimensional model based on DIVAST with suspended load and bed load transport has been developed to simulate the braiding processes and morphodynamic changes in braided rivers. In this model, the hydrodynamic equations are solved using the ADI scheme and the advective-diffusion equations are solved using a modified ULTIMATE QUICKEST scheme. The TVD scheme has also been included to simulate trans-critical flows. Regarding sediment transport, a new module based on bed load transport theories has been developed. A module for suspended load transport based on energy theory has been improved. Secondary flow and slope effect are integrated into the model by altering the sediment transport rate. A multiple layer technique with a vertical sorting process has been applied including bank erosion. Graded sediment fractions are adopted to represent the coarsening and fining processes with sheltering effect. The model has been verified by solving a 2-D dam-break problem which worked well in predicting the water surface changes in trans-critical flow. It has also been tested by a sediment aggradation case and found to predict the flow and bed deformation effectively. The model has been applied to predict a laboratory river with bed load, with its prototype being the Sunwapta River, Canada. Braiding mechanisms and channel pattern responses to abruptly increased discharge have been investigated and compared with those of laboratory and natural rivers. Growth and relationship of active braiding intensity and total braiding intensity show similar trends to those of iii the laboratory river. The predicted river shows anisotropic scaling with periodical braiding morphology presented by sequential maximum scour depths. The model also simulates a large idealised braided river with suspended load transport. Its braiding mechanisms have been discussed and compared with the river with bed load and natural rivers. Important processes at bars and confluences have been investigated. Statistical characteristics of the river have been analysed with braiding indices, state-space plots and bar parameters. These findings have been compared with those from real rivers to assess the model simulating real braided rivers.

The use of reverse-running pumps as turbines (PATs) is a promising technology for small-scale hydropower. This thesis reviews the published knowledge about PATs and deals with some areas of uncertainty that have hampered their dissemination, especially in 'developing' countries. Two options for accommodating seasonal flow variations using PATs are examined and compared with using conventional turbines (that have flow control devices). This has been done using financial parameters, and it is shown' that, under typical conditions, PATs are more economic. The various published techniques for predicting the turbine-mode performance of a pump without expensive tests are reviewed; a new heuristic one is developed, and it is shown (using the same financial parameters and a large set of test data in both modes of operation) that the cost of prediction inaccuracy is negligible under typical circumstances. The economics of different ways of accommodating water-hammer are explored. Finally, the results of laboratory tests on a PAT are presented, including cavitation tests, and for the latter a theoretical framework is exposed.

This thesis describes the implementation of general Computational Fluid Dynamics (CFD) techniques to laboratory and natural channels under flood flow conditions. Two commercially available codes, TELEMAC and CFX4, have been used in this work. The assessment of CFD for the calculation of flooded channel flow dynamics is carried out by simulating one laboratory test case from the Flood Channel Facility (FCF) Series B. This test case is that of a meandering two-stage channel with a depth ratio of 25% on the flood plain. Results from a computer simulation of experiment B23 are presented with a detailed quantitative comparison of the measured velocity, turbulence and bed shear stress. It supports the conclusion that CFD is able to account for the different flow mechanisms arising from the interaction between inbank and overbank flows in meandering channels. The maximum error in the prediction of the velocity is 10% and the comparisons show the calculations of bed shear stress to be reasonably accurate as well. Numerical tests indicate that the numerical solution is relatively independent of the boundary conditions, and confirm that turbulence transport is of minor importance in the experiment simulated. Numerical results from the simulation of flood flow mechanisms in natural rivers are also presented. It is hoped that these are of value to practitioners. Two 1-km reaches on the River Severn and River Ribble are modelled. They permit the investigation of two-stage channel flow dynamics at a larger scale. The numerical verification process establishes that the scale and the complex nature of the geometry are limiting factors, particularly for the numerical discretization of the domain and the calculation of the variables at the walls. It is however possible to estimate a priori part of the error such constraints generate. Away from the walls, the flow main features seem well predicted. The parallel between the velocity fields observed in river flood flows and those observed in the FCF is evident. Validation against field data suggests that the models are able to reproduce the flow mechanisms and account for bed shear stress variations correctly. Yet a significant level of uncertainty remains when the model predictions are compared against measured point data; more validation work is therefore required.

The two aims of this work were: (1) to develop a theoretical technique for determining the conditions where a broach would occur, and (2) to identify the principal factors affecting the liability of a ship to broach. The first step was to develop a mathematical model based on the conventional manoeuvring equations with coefficients which were functions of the ship's longitudinal position in the wave, but independent of encounter frequency. Next, a theoretical method for calculating the values of some of the coefficients as functions of wave position was developed using a strip theory approach and the results compared with those obtained experimentally. The experimental technique involved using a planar motion mechanism to oscillate a constrained model balanced on a wave created by a wave dozer in a circulating water channel. Although the agreement was poor and experimental scatter high for some of the coefficients, the more important ones were predicted quite well using the theory. Constrained model experiments were also --carried out in calm water in order to determine the approximate value of the roll coupling terms and it was found that, since they were small, the roll equation could be ignored as a first approximation. It was then possible to study the stability of the lateral and longitudinal motions separately for various wavelengths and to determine that the principal factor causing a broach was the large wave induced yaw moment combined with the small restoring moment available from the rudder operating with reduced effectiveness. The lateral and longitudinal equations were then combined using a digital/analogue hybrid simulation permitting the conditions which caused a broach to be determined. When the results from the simulation-were compared with results which had already been carried out by the Admiralty Marine Technology Establishment at Haslar there was fairly good agreement, implying that this method could be used to determine whether a proposed design would meet an acceptable standard. Finally, possible improvements to the simulation were suggested and guidelines for reducing the liability to broach were given both for the operator and the designer.

This thesis is based on the application of hydraulic modelling techniques to the study of river rehabilitation schemes. River channelization and rehabilitation techniques are reviewed and the restoration of the River Idle is detailed. The rehabilitation of the Idle, consisting principally of the installation of a number of flow deflectors, forms the basis of the modelling work carried out. Open channel modelling techniques are reviewed and the packages ISIS, HEC-RAS, SSIIM and CFX are applied to the River Idle. Results from SSIIM (two dimensional) and CFX (three dimensional) are validated against site measured velocities. SSIIM predicted velocities calibrate poorly against site data whilst CFX results are considerably more encouraging. Reasons for the increased accuracy of the three dimensional results are discussed. The effect of the installation of the flow deflectors on aquatic habitat is simulated using the techniques underlying the Instream Flow Incremental Methodology (IFIM). The results from the one dimensional model ISIS and the three dimensional package CFX are used to make available habitat predictions. Results indicate an improvement in habitat for adult and spawning chub but a worsening of habitat for roach fry. However, habitat for roach fry can be expected to improve with time as the geomorphology of the river responds to the installation of the deflectors. The results from the habitat modelling exercise also indicate significant discrepancies between the results obtained by applying the one and three dimensional models. Greater improvements in habitat are indicated in the results from the three dimensional modelling approach. This can be attributed to a number of factors but most significantly the fact that the three dimensional model, in solving two further momentum balance equations, accurately simulates a plume of higher velocity which is produced by the narrowing of the channel width at the deflector. This plume of higher velocity is propagated downstream for some distance beyond the deflector and is associated with improved habitat suitability in the case of adult and spawning chub. The effect of the deflectors on the movement of sediments in the Idle is simulated using ISIS Sediment, a module of the ISIS package, and SHEAR. SHEAR is a FORTRAN program, written for this thesis, which calculates bed shear stresses from the vertical velocity distribution predicted by CFX. The predicted bed shear stresses are compared with a critical shear stress for erosion which is calculated from the Shields criteria. Deposition areas can be implied from zones of reduced bed shear stress. Thus, SHEAR is able to describe the spatial detail of erosion and deposition, for any given sediment particle size, at a specific discharge. Results from ISIS Sediment and SHEAR are compared qualitatively with site measurements of bed erosion that has taken place at a single deflector site. Results indicate that the programs have successfully reproduced the major features of the movement of sediments observed on site. These consist of the erosion of a scour pool adjacent to the deflector tip and deposition in the lee of the deflector leading to the development of a bank of sediment. Overall, significant benefits are indicated in a three dimensional approach over the more traditional one dimensional models. These are evident in both improved calibration with site measured velocities, better available habitat prediction and the ability to describe the spatial detail of erosion and deposition.

The thesis is concerned with an investigation of the possibilities of generating metric information and carrying out topographic mapping operations from side-looking radar images acquired from Earthorbiting satellites, as exemplified by the synthetic aperture radar (SAR) system flown onboard the Seasat satellite, Besides the theoretical analysis of the problem, several images covering test areas with different topographic characteristics have been used for extensive and comprehensive tests of the geometric accuracy of the SAR system; for experiments with digital monoplotting techniques applied to the SAR images; and for tests concerned with the detection and"interpretation of objects appearing on these images. The results show that metric information of a limited accuracy can be obtained from satellite SAR images. This could act as the basis for reconnaissance-type mapping at scales of 1: 250,000 and smaller. The geometric accuracy actually achieved does, however, depend heavily on the method used initially to process the SAR image data. In this respect, the results obtained with the digitally processed images are superior to those obtained with the optically processed images. The influence of the topographic relief present on the ground is also noticeable and various techniques have been devised and used to eliminate or substantially reduce this effect. The use of digital monoplotting techniques did not produce as good or as complete a rectification as expected due to the difficulties experienced with the interpretation of the terrain objects recorded on the SAR images. These result partly from the constraints in imaging direction that are an inherent feature of SAR imaging and which make the detection and interpretation of certain objects on an SAR image rather arbitrary. A further difficulty is the presence of background clutter on all the Seasat SAR images but which is especially noticeable on the optically processed images tested. At the present stage of the development and application of satellite SAR imagery for mapping, the limitations are centered around shortcomings in the image resolution and quality rather than the geometric characteristics of the imagery or the rectification techniques which have been devised and implemented for mapping purposes.