The objective of this work was to examine the impact of unsteady flows on the erosion and movement of mixed grain size sediment. Time varying flows were examined as flowrates in natural rivers are rarely constant. There are very few reported studies on the movement of sediment in unsteady open channel flow and most of those used single sized sediment. River reach has its own sedimentological character and non-uniform beds exhibit very different behaviour from that of single sized material. Therefore it was thought important to examine the impact of time varying flow on the stability of water worked mixed grain size sediment beds. The thesis reports on a series of laboratory experiments in which a bimodal sediment bed was exposed to different flow hydrographs. The flow hydrographs consisted of constant flowrate with different duration and time varying flows with different rising and falling limb but had the same peak flowrate. Each experiment was followed by a stability test in which a standard "triangular shaped hydrograph" was used to assess the stability of each water worked deposit. The stability observation demonstrated that grain size fractions have different thresholds of motion when beds are formed by different antecedent flow patterns. The bed stability increased as the antecedent constant flow hydrograph progressed. The rising and falling limbs of the flowrate hydrographs were found to have a significant effect on the bed stabilisation process. It revealed that the shortest rising limb of flow hydrograph formed the weakest bed while the longest recession limb of flow hydro graph formed the most stable bed. It is believed that the short period of flowrate acceleration did not allow the coarse grains to stabilise with numerous exposed large grains spread on the bed. In a longer duration of recession limb of hydrograph, the coarse grains moved and eventually deposited over a length of time. As the flowrate declined the finer grains also rolled and then deposited forming a strong bond with the coarse grams. These experiments also provided important information on the flow structures and the changes in the bed topography as the tests progressed. There is strong evidence that only upward interactions (ejections) with high momentum magnitude were able to transport coarser grains. The lack of change in the distribution of downward looking-bed interactions (sweeps) in all tests indicated that these features are not important in determining transport. Changes in bed topography were also measured and characteristics of the distribution of bed surface elevation were linked to the observed changes in bed stability.

A commercial CFD (Computational Fluid Dynamics) code CFX (version 4.2 to 4.4) from AEA Technologyl'' has been used to compute the fluid flow, power number, Po, the stresses on baffles, mixing time and a precipitation reaction in a mixing vessel. The impellers investigated were Rushton turbine and 4 or 6 blade 45° pitch blade turbine. The impeller generated flow was modelled primarily using the sliding mesh technique, with additional modelling using Multiple Frames of Reference (MFR) for the mixing time simulations. The Po was estimated from three different methods i.e. specific energy dissipation rate, ET, summation, torque acting on the impeller surfaces, POp(primary power number), and the reaction torque acting on the vessel walls and baffles, POs (the secondary power number). The Po from the summation of ET, was underpredicted as compared with experimental values in all the simulations by over 50%. The investigation of the calculated power numbers for the vessels found that the closest and most consistent values of Po compared to experimental results were obtained from the torque acting on the impeller surfaces, POp. The value of POs was found to be greatly dependent on the sliding mesh simulation parameters and an improvement in the POsprediction could be obtained by using a small time step. A further investigation lead to the computation of the tangential forces and subsequently the axial pressure distribution on the baffles. The baffle pressure distribution depends on the impeller type and its clearance and was better predicted for greater impeller clearances and for the radial flow impellers. The mixing times simulations were performed using a computational method analogous to the experimental method of probe responses. The system was in the high transitional flow regime (Re=8800) and a low Reynolds k-e turbulence model was used in the development of the flow field. The simulations were compared with experimental results (based on decolorisation technique) and to three different mixing time correlations giving mixing times at three different levels of homogenisation (i.e. 90%, 95% and 99%). Worryingly, the simulation results were found to depend on the radial feed position even though the experimental results suggest that it does not. At certain radial position, the simulated mixing time responses accurately predicted the mixing times from the experiments and empirical correlations. CFD based flow visualisation showed that the feed position influenced where the majority of the tracer was initially distributed. The further the radial position was from the axis of the impeller, the more the bulk of the tracer moved towards the low velocity region near the vessel walls, leading to an overestimate of the mixing time. The sliding mesh and MFR simulations of the velocity fields were used for the computation of the mixing time. The results were similar in each case. The precipitation modelling was achieved through the coupling of the CFD hydrodynamics and user defined precipitation model. This approach was able to predict the performance of a semi-batch process involving the precipitation of BaS04 with 270 s addition time. The results (i.e. mean crystal size (d[4,3]) and the particle size distributions) were compared with experimental results for a double feed precipitation reaction for a number of feed configurations and concentration ratios. Overall reasonable trends and agreement have been obtained for the modelled Po, mixing time and baffle stresses. The precipitation model was less successful and was very dependant on the different crystal shape factors used in the simulation model. Further experimental work is required in order to define this parameter accurately, especially as experiments have shown that it varies during the addition time.

Colletotrichum gloeosporioides is the causal agent of anthracnose disease of mangoes. Infection occurs when humidity is high and rain-dispersed spores germinate and form an appressorium on immature mangoes. The infection then becomes quiescent until the fruit is harvested. On ripe fruit infection is visible as black, sunken lesions on the surface. At the pre-harvest stage, the disease is controlled with the application of a range of fungicides, and at the post-harvest stage by hot benomyl treatment. The extensive use of benomyl, both pre- and post-harvest, has resulted in the occurrence of isolates of C. gloeosporioides resistant to this fungicide. To devise an alternative strategy of disease control, the potential for biological control of anthracnose has been investigated. Potential microbial antagonists of C. gloeosporioides were isolated from blossom, leaves and fruit of mango, and screened using a series of assay techniques. In total 650 microorganisms, including bacteria, yeasts and filamentous fungi, were isolated and tested for their inhibition of growth of C. gloeosporioides on malt extract agar. Of these 650 isolates, 121 inhibited the fungus and were further tested on their ability to inhibit spore germination in vitro. Of these, 45 isolates, all bacteria and yeasts, were inoculated onto mangoes, which were artificially inoculated with C. gloeosporioides, and assessed for their potential to reduce the development of anthracnose lesions. A further selection was made, and 7 isolates were chosen to be used in a semi-commercial trial in the Philippines. This final screening procedure yielded two potential candidates for field trials, isolate 204 (identified as Bacillus cereus) and isolate 558 (identified as Pseudomonas fiuorescens). A field trial involving pre-harvest application of the biological control agent, was conducted using isolate 558. This isolate was chosen for this purpose since in in vitro experiments it significantly reduced germination of C. gloeosporioides spores. In the field trial 558 was applied in combination with nutrients and compared to treatments which had received no treatment or which had received conventional fungicide (benomyl) application. On spraying, high numbers of 558 were recorded on the leaf surface, but no reduction in post-harvest development of disease was observed. Failure of disease control was attributed to rapid death of the bacterium on the phylloplane. Inpost-harvest trials, isolates 204 and 558 were both tested in combination with different application methods, including the addition of sticker, peptone, fruit wax or a sucrose polyester. Application of 204 did not reduce disease development. Application of 558, however, did significantly reduce anthracnose development compared to the control fruit. No additional benefit was achieved by incorporating the bacteria in peptone, fruit wax or sucrose polyester. The mode of action of isolate 558 was investigated in detail. There was no evidence for parasitism taking place, or the production of volatile compounds, in the suppression of disease development. No antibiotic compounds were detected, but isolate 558 did produce a siderophore. A sharp increase in pH was also observed in culture media in which 558 was grown. Disease control may result from a combination of these two factors.particularly efficient in terms of storage requirements and computational speed. It also takes advantage of the nature of the system of equations to be solved. Several laminar benchmark exercises with and without heat transfer are performed. These include developing and fully developed isothermal duct flow, backward facing step flow, natural convection in square cavity and jet impingement with heat transfer. Results show that the adopted equal order velocity-pressure method can predict the benchmark solutions efficiently and accurately. Spurious pressure modes are also shown to be completely absent. In modelling turbulent flows, the k-c two equation eddy viscosity model is employed. The advection part of the k and e equations are discretised by the upwind technique developed in this research. Special treatment of the source terms eliminate the possibility of producing negative values of k or e during the iterative solution sequence, which can cause convergence difficulties. By combining the Law of the Wall and the Log Law of the Wall to determine shear stresses near solid regions, the need for an excessively fine mesh in these regions is avoided.

Open-channel flows are ubiquitous in nature and play a central role in many hydraulic engineering problems. This flow type occurs almost exclusively under fully-rough turbulent conditions and it is not uncommon for the relative submergence of these flows to be low. Despite this, most theory has so far been developed for smooth wall flows or rough-bed flows at high submergence while its applicability at low relative submergence remains questionable. This thesis therefore aims to contribute towards an improved understanding of turbulence structure in rough-bed open-channel flow at low to intermediate relative submergence. Experiments were conducted to collect turbulent velocity field data for nine different flow scenarios, covering roughness Reynolds numbers between 175 and 900, and relative submergence between 2.5 and 7.5. Each flow scenario was measured independently using particle image velocimetry (PIV) in five distinct configurations. The PIV system was first configured to make two-component velocity measurements with a very wide field of view (up to twenty flow depths) along the channel centreline in a streamwise-wall-normal plane. These measurements were supplemented with three-component stereoscopic PIV recordings along the same plane albeit with a shorter field of view. The third, fourth and fifth set ups involved stereoscopic PIV in three separate transverse-wall-normal planes and thus ensured the complete lateral coverage of the flow field from the sidewall to the centreline. The four-camera arrangement of each of the present stereoscopic PIV configurations was exploited to obtain velocity field statistics with significantly reduced contributions from measurement noise. The thesis reports distributions of bulk velocity statistics and spectra of all three velocity components. In addition, characteristic large scale features of the instantaneous flow are examined using velocity field visualisation, two-point velocity correlations and premultiplied velocity spectra. Further analysis is carried out on the time-averaged flow field to visualise secondary current patterns and to study their lateral extent.

No description available.

No description available.

Throughout the past decade, interest has grown in the use of boundary-fitted coordinate systems in many areas of computational fluid dynamics. The boundary-fitted technique provides an exact method of implementing finite-difference numerical schemes in curved flow geometries and offers an alternative solution procedure to the finite-element method. The unavoidable large bandwidth of the global stiffness matrix, employed in finite-element algorithms, means that they are computationally less efficient than corresponding finite-difference schemes. As a consequence, the boundary-fitted method offers a more efficient process for solving partial differential flow equations in awkwardly shaped regions. This thesis describes a versatile finite-difference numerical scheme for the solution of the shallow water equations on arbitrary boundary-fitted non-orthogonal curvilinear grids. The model is capable of simulating flows in irregular geometries typically encountered in river basin management. Validation tests have been conducted against the severe condition of jet-forced flow in a circular reservoir with vertical side walls, where initial reflections of free surface waves pose major problems in achieving a stable solution. Furthermore, the validation exercises have been designed to test the computer model for artificial diffusion which may be a consequence of the numerical scheme adopted to stabilise the shallow water equations. The thesis also describes two subsidiary numerical studies of jet-forced recirculating flow in circular cylinders. The first of these implements a Biot-Savart discrete vortex method for simulating the vorticity in the shear layers of the inflow jet, whereas the second employs a stream function/vorticity-transport finite-difference procedure for solving the two-dimensional Navier-Stokes equations on a distorted orthogonal polar mesh. Although the predictions from the stream function/vorticity-transport model are confined to low Reynolds number flows, they provide a valuable set of benchmark velocity fields which are used to confirm the validity of the boundary-fitted shallow water equation solver.

The investigation covers two possible areas of application of magnetic fluids, one involving the production of torque by means of rotating magnetic fields and the other the use Of magnetic fluids in the separation of non-magnetic ores on a density basis. The' emphasis-was upon the use of cheap, primitive ferrofluids Le'. non-collOidal suspension of relatively large particles. a Moskowitz and Rosensweig were the first to report electromechanical energy conversion with a rotating magnetic field. Their theory is not confirmed by their experimental results, howevert nor the fact that the fluid can rotate in the opposite direction to the field. This phenomenon has been investigated experimentally for a range of field intensities, wave velocities, particle sizes, volume loading and fluid viscosities. The torque per unit volume has been found to be related linearly to the volume loading but-nonlinearly to the frequency of the supply, field intensity and viscosity. For the primitive ferrofluids the results clearly indicate a combination of saliency and hysteresis torques. No satisfactory explanation for the reverse motion of the fluid has been produced and attempts to quantify the energy transfer have not been successful. Due to the inherently low permeability of the fluid, the torque per unit volume is much smaller than for conventional a. c. machines. Primitive magnetic fluids have also been shown to have potential in the separation of ores according to their densities. The novelty of this work is that the particles, which flocculate in the presence of stationary fields, are kept in suspension by agitation caused by a rotating wave. This agitation also serves to reduce the effective viscosity which at high volume loading can be high at zero field conditions. An effective specific gravity of about 12 has been obtained. The experimental results confirm the theory that the magnetic force in the linear condition is proportional to the magnetic energy - density gradient (in space) but with saturation the force is proportional to the field gradient and independent of body shape. A practical system seems to be feasible.

No description available.

No description available.