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Particle Image Velocimetry (PlY) is a technique for measuring instantaneous twodimensional fluid velocity fields from a chosen plane of interest within a flow field. This thesis presents new developments and applications of the technique which have been used to study both the non-reacting and reacting flow fields within cylindrical combustion chambers. Non-reacting, swirling laminar flow fields near the transitional flow regime have been investigated by both Computational Fluid Dynamics (CFD) modelling and PIV experiments. Direct comparisons between CFD, PlY and other published results are made and close agreements are found. Additionally, the PlY technique has been optimised by careful use of a thin laser illumination sheet and correct choice of laser pulse separation. This has enabled successful PlY measurements in the boundary layers of the flow field where high velocity gradients exist. The PlY technique has been applied to measure the flame development and propagation process within the chamber under both quiescent and swirling flow conditions. Representative sequences of PIV results at different flame propagation stages are obtained and the accuracy in the extraction of the flame location is discussed. They clearly reveal the instantaneous flame front position and the unburned gas velocity field simultaneously. These features provide further insight into the combustion process itself and also the interaction between the combustion and flow field. A new application of PIV, combined with a flame speed detection technique, has been proposed and developed to obtain direct measurements of the laminar burning velocity of combustible mixtures. The laminar burning velocity is determined as the difference between the flame speed and the unburned gas velocity immediately ahead of the flame front. PIV is used to measure the unburned gas velocity field and either a pair of ionisation probes or a laser beam refraction technique is used to measure the local flame speed simultaneously. The relative merits of each technique are compared. The laminar burning velocities of propane-air mixtures initially at atmospheric conditions for equivalence ratios ranging from 0.7 - 1.4 were measured. The measured values show close agreement with previously published results based on other techniques. The advantages and limitations of the PIV techniques used in this work are examined and the prospects of their improvement and further application are discussed.

This investigation aims to enhance the regeneration performance of a diesel particulate filter. This is achieved by introducing various chemical components to the regeneration process, which are representative of what can be generated ‘on board’ a vehicle using an exhaust gas fuel reformer. By researching the effects of introducing such components using a periodic injection cycle the aim is to reduce the volume of ‘reformates’ required to assist in proficient diesel particulate filter regeneration. As a result, this study also aims to support future work in the development of exhaust gas fuel reformer design for DPF aftertreatment applications. All experiments were performed using a Ford Puma 2.0 litre diesel engine. A test rig was constructed and installed that featured a mini diesel particulate filter housed within a tubular furnace. Exhaust gas could be sampled directly from the exhaust manifold and fed through the DPF. Exhaust gas measurements were taken both pre and post DPF using a FTIR spectrometer. It was shown that the regeneration process could be supported substantially by the introduction of hydrogen. Similar properties were also demonstrated when introducing a hydrogen-carbon monoxide mixture. The introduction of these species allowed for the regeneration process to be implemented at filter temperatures substantially lower than the passive regeneration temperature. Furthermore, by introducing these simulated reformates using a periodic injection strategy, it was evident that similar benefits to the regeneration process could be attained with significantly less volumes of simulated reformates. In an attempt to effectively utilise the carbon monoxide generated during hydrogen production by an exhaust gas fuel reformer, this study defined an optimised hydrogen/carbon monoxide mixture ratio of 60% (v/v) hydrogen balanced with carbon monoxide. At this optimised mixture ratio, the filter demonstrated the highest regeneration efficiency of all ratios tested. Such data could be utilised in future work in the development of fuel reformer design.

Non-physical arrivals produced by seismic interferometry, the process whereby Green’s functions are synthesized between two points by cross-correlation, crossconvolution or deconvolution, are often considered to provide little information about the Earth’s subsurface. Their contributions are usually suppressed in interferometric Green’s function estimates to suit existing methods of seismic velocity estimation which favour the more familiar physical arrivals. In this thesis we show that the non-physical arrivals retrieved in exploration-type settings are useful for determining the long-wavelength seismic velocity structure and can be used to obtain improved Green’s function estimates. First, we estimate the seismic velocity and layer thickness by measuring the signal coherency along traveltime curves between two receivers in a collection of traces consisting of cross-correlated wavefields, known as the correlation gather. The traveltime curves represent the traveltime differences between wavefields recorded at the two receivers. When the procedure is used to find the velocity and thickness of the uppermost layer, the traveltime curves implicitly incorporate the physical and non-physical wavefields in the Green’s function estimates. When the procedure is applied to a model with more than one layer, the traveltime curves correspond to non-physical wavefields only in the Green’s function estimates. Instead of suppressing multiple reflections as in conventional methods, the procedure incorporates the traveltimes of multiple reflections to constrain velocity and thickness estimates. The procedure above is most suitable for recovering the first-layer seismic velocity. We propose a simpler method to estimate the seismic velocities corresponding to deeper layers. We find that the Green’s functions contain very weak reflections, but are dominated by non-physical refractions if retrieved using a limited source aperture. The seismic velocities are easily identifiable as repeating bright spots after transforming the refraction-dominated Green’s functions to the − p domain. We show that non-physical reflections can be used constructively to provide physical reflections, and therefore improved Green’s function estimates, by using a cross-convolution operation in a new variant of seismic interferometry, called source-receiver interferometry. We also show that non-physical reflections associated with the cross-correlation of reflections from different interfaces allow for the direct estimation of interval velocities and layer thicknesses. This method removes the necessity to first find the root-mean-square velocities and two-way traveltimes required to compute the interval velocities by Dix inversion. Overall, this thesis significantly improves our understanding of how nonphysical energy in seismic interferometry both provides useful information about the Earth’s subsurface and contributes to physical energy in particular interferometric methods.

The generation of electricity from tidal currents is an emerging industry with the potential to contribute to the UK energy supply in a predictable and sustainable way. The development of the technology requires the cost effective subsea installation of energy conversion systems in an energetic and challenging marine environment. One concept developed for the fastening of tidal energy converters to the seabed is the Active Gravity Base (AGB), which offers potential reductions in installation cost and time, relative to existing fastening methods. The performance of this concept in response to unsteady flow conditions is explored within this thesis. The dynamic behaviour of a tidal current is driven by a range of factors from gravitational forces of celestial bodies to high-frequency fluctuations of turbulent eddies. The response of the AGB concept to the unsteadiness of tidal currents is herein considered under the two broad time-scales; the directionality of the mean semi-diurnal cycle and the high frequency variations from a given mean flow velocity. The correlation between the direction and velocity of the tidal flow was assessed using hourly averaged data provided by the Admiralty Charts in the northern UK waters. The resulting directionality model was used to predict the performance of the AGB under a range of quasi-steady flow conditions. High frequency velocity measurements of a potential tidal energy site were obtained through collaboration with the University of Washington and the Pacific Northwest National Laboratory. This data was used to estimate the maximum perturbation from the mean velocity that can be expected on an annual basis. An experimental facility was developed within the re-circulating water flume at the University of Edinburgh to examine the dynamic loads generated by controllable two-dimensional flow perturbations. This was successfully achieved using a configuration of twin pitching foils with independent motion control. A relationship between the foil pitch angle and velocity perturbation time series was predicted using a vortex model of the foil wakes. This configuration was shown to be able to generate significant flow fluctuations within the range of reduced frequencies 0:06 ≤ k ≤ 1:9, with a peak gust intensity of Ig = 0:5. The numerical solution was validated against experimental results.

This thesis describes research carried out to study steep streams. Step-pool sequences, a typical feature of such streams, were found to occur on every steep stream studied in the field. The most important control on the spacing of the steps was width. Flume experiments produced steps (at an average Froude number of 0.88), and showed that the presence of steps increased resistance to flow at lower than step-forming flow and decreased resistance at above step-forming flows. In the field, flow resistance was found to be controlled by sediment characteristics and the amount of step protrusion. The hydraulic geometry of the steep streams was also studied, and was found to differ considerably from hydraulic geometry characteristics of lowland streams. The formation of steps and pools was not found to be related to antidune processes; rather they were built up individually as large particles captured other large particles that had been entrained by the near critical flow. It was concluded that it is not the absolute values of slope and discharge that determines whether steps form. Near critical flow and high relative roughness appear to be the only requirements necessary. Previous equations were generally found to perform poorly when used with the experimental data, and an attempt to model the velocity profile using sediment characteristics and considering stresses on the flow also produced poor correlation with the actual field data. Modifications to these were made with some success, especially in the ability to predict friction factor based on relative roughness using D84 . Flume velocity profiles identified characteristic velocity profiles at different locations within the step-pool sequence and the presence 'S-shaped' profiles downstream of the step.

This study examined: 1) if estimated performance times (ETcom) at four different distances can be used to accurately define the parameters of the critical velocity (CV) test [CV and anaerobic running capacity (ARC)]; and 2) if those parameters can be used to predict time to completion (PTcom) of distances performed at velocities greater than CV. Twelve subjects provided an ETcom for maximal-effort runs at 400m, 800m, 1600m, and 3200m. The CV and ARC were derived from the total distance (TD) versus ETcom relationship. The equation: PTcom = ARC / (velocity-CV) was used to determine the PTcom for runs at 200m, 600m, and 1000m. The PTcom was validated against the actual time to complete (ATcom) runs at the same three distances. The TD versus ETcom relationship was highly linear and indicated a close relationship between running distance and time. The PTcom overestimated the ATcom at 200m, but was not different from ATcom at 600m and 1000m. The PTcom and ATcom were not related at any of the three distances. The CV model could be applied to estimated performance times to derive the CV and ARC parameters, but the parameters of the test did not accurately estimate performance times above CV.

Estimations of the intensity of short-period perturbations of the horizontal drift velocity at 80 - 110 km altitude are made using data from the regular low-frequency D1 ionospheric reflection observations at Collm, Germany (52° N, 15° E) for the period 1983 - 1999. A simple half-hourly-difference numerical filter is used to extract perturbations with time scales between 0.7 and 3 hours. The results are compared with the mean drift analyses in order to study the interaction between short-period perturbations and the mean circulation. The average monthly variances of short-period perturbations of the zonal velocity near 80 km altitude show a main maximum in summer, a smaller maximum in winter, and minimum values at the equinoxes. At higher altitudes the summer maximum is shifted towards spring, and another maximum of perturbation variances in autumn appears at altitudes near and above 100 km. The seasonal changes of variances of the meridional velocity show maximum values in spring and summer, also some indications for an increase of the summer maximum at altitudes larger than 100 km are found. The observed altitude changes of the seasonal variations of drift perturbation variances are consistent with some numerical calculations of the height structure of a spectrum of internal gravity waves in the middle and upper atmosphere. / Die Intensität kurzperiodischer Störungen der horizontalen Driftgeschwindigkeit im Höhenbereich zwischen 80 und 110 km wurde anhand der regulären D1 Langwellenreflexionsmessungen in Collm (52° N, 15° E), bestimmt. Verwendet wurden Daten der Jahre 1983 - 1999. Ein einfache numerische Filter basierend auf den Unterschieden aufeinanderfolgender halbstündiger Windmittelwerte wurde verwendet, um Störungen im Zeitbereich von 0.7 - 3 Stunden zu ermitteln. Die Ergebnisse wurden mit Analysen der mittleren Drift verglichen, um die Wechselwirkungen zwischen kurzperiodischen Störungen und der mittleren Zirkulation zu untersuchen. Die mittlere monatliche Varianz der kurzperiodischen Störungen der Zonalgeschwindigkeit bei etwa 80 km zeigt ein Hauptmaximum im Sommer und ein schwächeres Maximum im Winter, wobei die Minima während der Aquinoktien auftreten. In grösseren Höhen verschiebt sich das Sommermaximum zum Frühjahr hin, und in Höhen über 100 km erscheint im Herbst ein weiteres Maximum. Der Jahresgang der meridionalen Windstörungen zeigt maximale Werte in Frühjahr/Sommer, und es sind auch Hinweise auf eine Verstärkung des Sommermaximums oberhalb von 100 km zu finden. Die gemessenen Höhenänderungen im Jahresgang der kurzperiodischen Driftschwankungen entsprechen numerischen Ergebnissen der Höhenabhängigkeit interner Schwerewellen in der mittleren und oberen Atmosphäre.

This investigation is designed to find the net rate of decrease in the component of velocity parallel to the original direction of motion of a proton moving through an electron gas exhibiting a non-spherical velocity distribution.