This thesis investigates the hydrodynamics of flow around/and or above an obstacle(s) placed in a fully turbulent developed flow such as flow around lateral bridge constriction, flow over bridge deck and flow over square ribs that are characterized with free surface flow. Also this thesis examines the flow around one-line circular cylinders placed at centre in a single open channel and floodplain edge in a compound, open channel. *Hydrodynamics studies of compound channels with vegetated floodplain have been carried out by a number studies of authors in the last three decades. To enrich our understanding of the flow resistance, comprehensive experiments are carried out with two vegetation configurations-wholly vegetated floodplain and one-line vegetation and then compared to smooth unvegetated compound channel. The main result of the flow characteristics in vegetated compound channels is that spanwise velocity profiles exhibit markedly different characters in the one-line and wholly-vegetated configurations. Moreover, flow resistance estimation results are in agreement with other experimental studies. *A complementary experimental study was carried out to investigate the water surface response in an open-channel flow through a lateral channel constriction and a bridge opening with overtopping. The flow through the bridge openings is characterized by very strong variation of the water surface including undular hydraulic jumps. The results of simulation that was carried by (Kara et al. 2014, 2015) showed a reasonable agreement between measured and computed water surface profiles for the constriction case and a fairly good was achieved for the overtopping case. *Evaluation of the shear layer dynamics in compound channel flows is carried out using infrared thermography technique with two vegetation configurations - wholly vegetated floodplain and one-line vegetation in comparison to non-vegetated floodplains. This technique also manifests some potential as a flow visualization technique, and leaves space for future studies and research. Results highlight that the mixing shear layer at the interface between the main channel and the floodplain is well captured and quantified by this novel approach. iii *Flume experiments of turbulent open channel flows over bed-mounted square bars at low and intermediate submergence are carried out for six cases. Two bar spacings, corresponding to transitional and k-type roughness, and three flow rates, are investigated. This experimental study focused on two of the most aspects of channel rough shallow flows: water surface profile and mean streamwise vertical velocity. Results show that the water surface was observed to be very complex and turbulent for the large spacing cases, and comprised a single hydraulic jump between the bars. The streamwise position of the jump varied between the cases, with the distance of the jump from the previous upstream bar increasing with flow rate. The free surface was observed to be less complex in the small spacing cases, particularly for the two higher flow rates, in which case the flow resembled a classic skimming flow. The Darcy-Weisbach friction factor was calculated for all six cases from a simple momentum balance, and it was shown that for a given flow rate the larger bar spacing produces higher resistance. The result of the simulation that was carried out by Chua et al. (2016) shows good agreement with the experiments in terms of mean free surface position and mean streamwise velocity. *Drag coefficient empirical equations are predicted by a number of authors for an array of vegetation. The research aims to assess the suitability of various empirical formulations to predict the drag coefficient of in-line vegetation. Drag coefficient results show that varying the diameter of the rigid emergent vegetation affects significantly flow resistance. Good agreement is generally observed with those empirical equations. Key Words: Flow Visualization; Infrared Thermography; Shallow Flows; Shear layer; Image processing; Experiment; Free surface; Bridge hydrodynamics; Bridge overtopping; Vegetation roughness, Emergent vegetation, Drag coefficient, blockage; Compound channel, Lateral velocity profiles; Hydraulic resistance; Hydraulic jump, Square bars.

The vortex fluctuations have proved to be responsible for the onset of dissipation in thin type-II superconducting Aims. There is also growing evidence that dissipation in high- temperature superconductors exhibits the same kind of two-dimensional (2D) behavior. However, a proper analysis of these materials requires a thorough understanding of the two-dimensional fluctuations. This thesis may be considered to consist of two parts. The first is concerned with two models that have often been used as models for 2D superconductors, the 2D Coulomb gas and the 2D XY model. The second part contains analyses related to high-temperature sup er conductivity. Through analysis of some renormalization equations for the Kosterlitz-Thouless (KT) transition, it is shown that the region governed by the KT critical behavior is very small and only applies at very low values for the flux-flow resistance. It is concluded that this critical behavior not is observable in superconductors, and, furthermore, that the only available method to test for 2D fluctuations at the onset of resistance, is through comparison with the 2D resistance scaling function. The critical temperature for the 2D XY model is determined by means of a finite- size scaling relation for the helicity modulus. The linearly screened potential in the XY model is written in terms of a correlation function. The analogy to the 2D Coulomb gas is found to be exact with a temperature-dependent bare interaction and a new expression for vorticity. It is also demonstrated that the Coulomb gas scaling concept may be applied to XY-type models. An analysis of resistance data for YBCO/PBCO superlattices in terms of the 2D resistance scaling function gives evidence for 2D behavior in the cases with large separation of the superconducting layers. In the superlattices with stronger interlayer coupling, the crossover to three-dimensional behavior is seen as a deviation from the scaling function as Tc is approached from above. The anisotropic three-dimensional (3D) XY model is examined as a model for high- temperature superconductors. It is shown that the density of vortices above Tc are closely equal in the anisotropic 3D model and the 2D model. This is taken as evidence that the 3D to 2D crossover found in the superlattices also is present in the anisotropic 3D XY model. / digitalisering@umu.se

The objective of this thesis is to reach theoretical understanding of the unusual relationship between charge-ordering and superconductivity in correlated-electron systems. The competition between these broken symmetries and magnetism in the cuprate high temperature superconductors has been extensively discussed, but exists also in many other correlated-electron superconductors, including quasi-two-dimensional organic charge-transfer solids. It has been suggested that the same attractive interaction is responsible for both charge-order and superconductivity. We propose that the specific interaction is the tendency in correlated-electron systems to form spin-singlet bonds, which is strongly enhanced at the commensurate carrier density p of ½ a charge carrier per site, characteristic of all superconducting charge-transfer solids. To probe superconductivity driven by electron correlations, a necessary condition is that electron-electron interactions enhance superconducting pair-pair correlations, relative to the non-interacting limit. We have performed state of the art numerical calculations on the two-dimensional Hubbard model on different triangular lattices, as well as other lattices corresponding to K-BEDT-TTF based organic charge transfer solids, for the complete range of carrier densities per site p (0 ≤ p ≤ 1). We have shown that pair-pair correlation for each cluster is enhanced by electron-electron interaction only for p ≃ 0.5, far away from the density range thought to be important for superconductivity. Although initial focus is on charge-transfer solids, the results of the research will impact the field of correlated electrons as a whole. We believe our calculations will provide fundamental and fresh insight to the theory of superconductivity in strongly correlated systems.

This study focussed on the treatment of stormwater runoff using constructed wetlands (CWs): man-made systems engineered to replicate the treatment processes in natural wetlands. The main aims were to design and assess a novel configuration of CWs for stormwater treatment, while contributing to the further understanding of pollutant removal in CWs through the development of models to explain internal processes and predict performance. A vertical tidal-flow CW operational regime was applied to target enhanced nitrogen removal while maintaining high removal rates a range of high priority urban stormwater pollutants. Eight pilot-scale CW models were built to investigate the effect of key design and operational variables: substrate media, wetland surface area, and wetting and drying regimes. The performance of the systems was considered successful when compared to results of similar pilot-scale CWs that operated without tidal flow. Results show that all eight models effectively reduced concentrations of solids and metals, with load reductions generally in excess of 90%. Nutrient removal – particularly nitrogen - was heavily affected by design and operation variables. Significantly, nitrogen removal in the systems outperformed similar pilot-scale CWs with alternative hydraulic operating conditions. Understanding of the internal CW treatment processes were backed up through statistical analysis and numerical modelling. These techniques highlighted important mechanisms such as the biological transformation of nitrogen and the importance of TSS removal to heavy metals reduction. Overall, results show that the CW design has great potential for reduction of solids, metals and nutrients in stormwater. Further research at a field scale would better represent the performance of the systems in practice, and closer monitoring of dissolved oxygen and redox potential would enhance understanding of internal processes, particularly regarding nutrient behaviour. Results of this study can contribute to future CW research and design, through increased understanding of long-term pollutant removal in these types of system. In time, this may result in the wider application of CWs for stormwater treatment to make human water use more sustainable and better protect the environment.

No description available.

Road safety is a very important topic for research and development divisions in the automotive industry. As the tyre is the only link between road surface and vehicle, it plays a very significant role in accident mitigation and prevention. This thesis investigates the influence of internal tyre pressure on the brake distance both experimentally and theoretically. Brake tests were performed using a robotic system and a winch was used to pull a car with locked wheels. For both experiments, the tyre pressures were changed. A rubber friction law is presented which can be used for tyre and vehicle dynamics calculations. The friction law was tested by comparing numerical results to the full rubber friction theory of Persson and to experimental data. A two-dimensional (2D) tyre model is introduced that combines the rubber friction law with a simple mass-spring description of the tyre body. The tyre model is very flexible and can be applied to different manoeuvres. It can be used to calculate μ-slip curves, self aligning-torque, braking, and cornering, or combined motion (e.g. braking during cornering). The theoretical predictions have been compared to measured data from indoor tyre testing on sandpaper substrate. Additionally simulations of anti-lock braking system (ABS) using two different control algorithms are presented. In addition a method for rapidly changing the tyre inflation pressure while a vehicle is in motion is presented. This method can be used for novel safety system approaches.

In the international oil and gas industry multiphase annular flow in pipelines and wells is extremely important, but not well understood. This thesis reports the development of an efficient and cheap method for measuring the phase flow rates in two phase annular and annular mist flow, in which the liquid phase is electrically conducting, using ultrasonic and conductance techniques. The method measures changes in the conductance of the liquid film formed during annular flow and uses these to calculate the volumetric and mass flow rates of the liquid film. The gas velocity in the core of the annular flow is measured using an ultrasonic technique. Combined with an entrainment model and the liquid film measurements described above, the ultrasonic technique enables the volumetric flow rate of the gas in the core and the volumetric and mass flow rates of entrained liquid droplets to be measured. This study was based on experimental work and the use of modelling techniques. The practical investigation comprised a series of experiments conducted on a purpose built flow loop in which the test section was a Perspex pipe of 50mm ID. The experimental work was limited to two-phase air-water flow. The flow loop was specifically designed to accommodate the different instruments and subsystems designed in this investigation including bespoke flow meters and a film extraction system. Most flow loop controls were automated using a MATLAB program. Reference measurement of the total water flow rate was made using a calibrated turbine flow meter and of the air flow rate using a calibrated rotameter. For the combined ultrasonic/conductance method investigated in this thesis, the velocity of the gas in the core was found using a novel Ultrasonic Flow Meter (USFM). The positioning and arrangement of the transducers have never been used previously. The flow velocity of the liquid film and the thickness of the film were measured using a novel Conductance Flow Meter (CFM). The CFM measured the liquid film thickness using novel wall conductance probes. By cross correlating the signals from a pair of such probes the film velocity was obtained. Good agreement of the experimental results obtained from the CFM and USFM with results published in the literature was found. Although not investigated experimentally in the work described in this thesis, annular flows encountered in the oil industry may contain a liquid phase comprising a mixture of oil and water. For such flows, the volume fractions of the oil and water can be measured using an automated bypass system developed during this project. The bypass system periodically extracts part of the liquid film, measures its density and then releases the sample back into the pipeline. The liquid phase volume fractions are determined from this density measurement which can be performed more than once per minute. An entrainment model was developed, which is required by the ultrasonic/conductance flow metering technique described in this thesis, in which the mass fraction of the liquid flowing as entrained droplets in the core can be determined from the liquid film thickness and velocity measurements. A mathematical model was also developed to describe the properties of the liquid film, such as liquid velocity profile within the film, and the model’s results were found to agree with the experimental results obtained during the project and also with previous work cited in the literature. The complexity of this latter model was reduced by making a number of simplifying assumptions, which are presented and discussed in the thesis, including the assumption that in annular flow there is a dynamic balance liquid entrainment and droplets being deposited back onto the film. The combination of the designed CFM and USFM with the bypass tube and the entrainment model offer the opportunity for a ‘wet gas’ flow meter to be developed to measure two and three phase annular flows at relatively low cost and with enhanced accuracy. Such a device would have the advantage that it would by substantially smaller than systems using separators and it could even be retrofitted onto off-shore platforms. The integration of the subsystems developed in this project into a single system capable of giving on-line measurements of annular flow would be a major benefit to the author’s sponsor, Petroleum Development of Oman.

No description available.

No description available.

The use of satellite altimeter data for spatial mapping of the wave resource is examined. A new algorithm for estimating wave period from altimeter data is developed and validated, which enables estimates of wave energy converter (WEC) power to be derived. Maps of the long-term mean WEC power from altimeter data are of a higher spatial resolution than is available from global wave model data. They can be used for identifying promising wave energy locations along particular stretches of coastline, before a detailed study using nearshore models is undertaken. The accuracy of estimates of WEC power from wave model data is considered. Without calibration estimates of the mean WEC power from model data can be biased of the order of 10-20%. The calibration of wave model data is complicated by non-linear dependence of model parameters on multiple factors, and seasonal and interannual changes in biases. After calibration the accuracy in the estimate of the historic power production at a site is of the order of 5%, but the changing biases make it difficult to specify the accuracy more precisely. The accuracy of predictions of the future energy yield from a WEC is limited by the accuracy of the historic data and the variability in the resource. The variability in 5, 10 and 20 year mean power levels is studied for an area in the north of Scotland, and shown to be greater than if annual power anomalies were uncorrelated noise. The sensitivity of WEC power production to climate change is also examined, and it is shown that the change in wave climate over the life time of a wave farm is likely to be small in comparison to the natural level of variability. It is shown that despite the uncertainty related to variability in the wave climate, improvements in the accuracy of historic data will improve the accuracy of predictions of future WEC yield. The topic of extreme wave analysis is also considered. A comparison of estimators for the generalised Pareto distribution (GPD) is presented. It is recommended that the Likelihood-Moment estimator should be used in preference to other estimators for the GPD. The use of seasonal models for extremes is also considered. In contrast to assertions made in previous studies, it is demonstrated that non-seasonal models have a lower bias and variance than models which analyse the data in separate seasons.