The motivation for this research is a proposed UHF surface wave communication system in which the waveguides are the stranded, overhead earth wires of Power System transmission lines. Attention is confined largely to an investigation of certain aspects which affect the overall surfaces wave transmission loss, a full-scale system having been set up in the laboratory for experimental purposes. For the prediction of transmission loss the stranded conductor is assumed to be equivalent to a solid conductor of the same diameter but with surface anisotropy in the form of two mutually orthogonal surface impedances the major reactive component of which is attributed to the effects of the helical stranding. This reactance is determined from a consideration of the fields which are assumed to exist within the cavities between the strands, and externally. From a comparison between experimental and theoretical loss characteristics there is sufficient inducement to accept the anisotropic model of the stranded conductor for practical design purposes. Approximate equations are developed to simplify the calculation of transmission loss and the notion of ‘capture cross-section’ is employed for the estimation of the efficiency of conical horn launchers. It is deduced from ‘sensitivity’ relationships that the horn loss is relatively insensitive to small changes in the fictitious surface reactance representing the effects of helical stranding, which tends to justify the assumptions upon which the anisotropic model is based. On the other hand, variations in the helix angle are shown to have a marked effect upon the calculated horn loss. This influences the choice of the stranded conductor used as the waveguide for the experimental verification of the model. The Author’s experimental research is described at length, the principal objective being to establish the anisotropic model as an acceptable theoretical substitute for the stranded conductor. To reduce the horn loss, dielectric sheaths are ted to the waveguide in the vicinity of the horn apertures. The discrepancies which then appear between theory and experiment are attributed both to the scattering of the surface wave by the boundary discontinuities at the ends of the sheaths and to the anomalous behaviour of commercial-grade PVC dielectric. Considering the increase in the transmission efficiency which may be realised by fitting dielectric sheaths to the conductor near the horn apertures it is concluded that a theoretical investigation of the scattering properties of the discontinuities s in order. Thus, the remainder of the Thesis is devoted, to this scattering effect as it may be encountered in the proposed scheme, the theoretical analysis following the lines of earlier documented research. A short-cut method is applied for the determination of certain ‘half-plane’ functions which appear in the expressions for the scattered power. Theoretical results are presented together with a discussion of some experimental measurements and a brief theoretical examination of the effects on the horn loss of varying the thickness of the dielectric sheaths. It is argued that the horn loss may be reduced if the dielectric thickness is graded in steps to a value at the horn apertures consistent with the desired ‘power capture’. The Thesis is concluded with an Addendum which outlines a number of topics suggested by the Author for future research.

Although the current thermoacoustic theory has so far proved successful in allowing us to analyse and understand thermoacoustic systems, there are inherent limitations associated with it. These are related to the fact that this theory is based on linear approximations. As designers search for ways to increase the efficiency and power density of thermoacoustic devices the accuracy of the linear theory decreases significantly, as a variety of non-linear effects start to become important. For example, when the pressure amplitude is increased, in order to increase the power density. This thesis concentrates on the non-linear effect of acoustic streaming. Acoustic streaming is a steady flow that is superimposed upon the acoustic Oscillations. An expression for the streaming velocity is developed for a parallel plate channel having an arbitrary gap width, so that the solution is valid for both thin and wide boundary layers. The solution includes thermal effects arising from the presence of an axial temperature gradient along the channel, and arbitrary phase between the pressure and velocity. An essential feature of the streaming velocity is the generation of circulating loops, which can cause heat to be convected within the channel. An expression for the transverse steady state temperature was also derived, for similar conditions as outlined for the streaming velocity. It was found that when an axial temperature gradient is present the magnitude of the transverse steady state temperature increases significantly as the width of the channel increases. The implication of this is that a significant amount of heat can be convected along the channel due to the action of the streaming velocity. When no axial temperature gradient is present, the transverse steady state temperature reduces to a small constant value outside the boundary layer. A numerical finite difference scheme was developed to model non-linear flow within the two-dimensional channel. The model solves for the conjugate fluid-solid problem enabling the temperature difference induced along the channel to be predicted. The model compared very well to experimental data. It was also found to be in excellent agreement with the analytical solutions for the streaming velocity and the transverse steady state temperature. The effect of streaming on the energy flux density was examined for a wide channel, having a temperature gradient along its length. A fourth-order expression was developed, which yielded a solution in terms of the transverse steady state temperature and second-order mass flux, which for certain conditions could be of a similar magnitude as the second-order terms. For a thermoacoustic core, it was proposed that a toroidal flow could form and convect heat from one heat exchanger to the other. To analysis this effect toroidal flow was incorporated into an expression for the temperature difference induced across a thermoacoustic couple. This result was found to be in excellent agreement with experimental data. The effect of toroidal streaming on the thermoacoustic core was also considered. In addition, a second-order expression for the work flux was derived that included a previously ignored term due to acoustic streaming.

This study is concerned with a theoretical, laboratory and in situ investigation of the propagation of seismic stress waves through soil media. Analyses are carried out to predict the surface response that results from earthquake motions being transmitted through the upper layers of the earth. The nature of the near surface geological layers affect to a marked degree the intensity of surface motion. The mathematical models presented are used in the evaluation of site response to earthquakes. The theoretical methods used depart from the traditional viscoelastic approach and use a nonlinear hysteretic soil model to describe the complex dynamic stress-strain relationships evident in soil response. The dynamic soil model is based on previous laboratory work carried out at this university. The theoretical solutions formulated are limited to one-dimensional situations. Three methods of analysis are presented for the propagation of seismic shear waves through nonlinear soil media and conclusions are drawn as to the best approach. The results of these analyses are generally significantly different from those obtained using a viscoelastic soil model. Seismic dilatational waves are also considered important and a method is presented to calculate the response of hysteretic soil media to these disturbances. The outcome from these dilatational and shear wave analyses is more accurate surface response spectra for use in aseismic structural design.

The design of rubble mound breakwaters is typically based on empirical formulae and physical modelling. One limitation of this approach is that different aspects of wave interaction with a breakwater, such as the elevation of the runup tip and armour stability, are treated separately. Therefore the development of a numerical model of wave runup on a rubble mound breakwater was the primary objective of the research described in this thesis. Because of the range of slope conditions encountered with rubble mound breakwaters and revetments, two types of armour layer are considered. The first is impermeable and so only the flow within the external region is modelled. The flow is assumed to be governed by the unsteady one-dimensional shallow water wave equations and only regular waves are considered. It is shown how the use of the finite element method with a mesh of isoparametric elements that deforms and is fitted to the runup tip has a number of advantages over the traditional use of the finite difference method with a fixed grid. Reasonably good results were obtained for the numerical modelling of wave runup on a riprap armoured l:3 impermeable slope indicating that the numerical model may, in conjunction with a physical model, be of practical use in the design of revetments. Wave runup on smooth and Dolos armoured 1:1.5 impermeable slopes was modelled poorly. Therefore the model is more appropriate for wave runup on a revetment than a rubble mound breakwater. The second type of armour layer is permeable and so the flow within the external region and armour layer is modelled simultaneously by coupling numerical models for the respective regions. It is concluded that this approach is unlikely to give acceptable results for the runup of regular waves on a steep, permeable armour layer unless it also accounts for the non-hydrostatic distribution of pressure within the external region. An experiment is described in which continuous time histories of wave runup and dynamic pressure due to regular waves on smooth and Dolos armoured 1:1.5 slopes were measured. The results are used to discuss the assumption of hydrostatic pressure. A method of assessing armour stability requirements which takes into consideration the effects of armour unit interaction is proposed. It is recommended that this is examined further.

A new theoretical characterisation is developed for the off-axis stiffness of FRP materials. The theoretical model treats an off-axis unidirectional ply as an inhomogeneous material, and considers the effect of rigid body rotations of the fibres within the matrix material. Linear analytical, and nonlinear finite element solutions are developed for the model. The differences between the new model and the traditional homogenous orthotropic characterisation are functions of both the strain level, and the relative modulus ratio (Ef/Em) of the constituent materials. For relative constituent moduli typical of most common FRP materials, there are significant differences between the new Rigid Body Motion (RBM) model and homogenous orthotropic characterisations at strains greater than 1%. In a 30° case with Ef/Em = 100 and a strain level of 2%, the RBM theory predicts a longitudinal modulus 11% higher than the linear orthotropic theory. At small strain levels the RBM theory reduces to the homogenous orthotropic approximation. A simple and reliable methodology is developed and verified for the experimental characterisation of off-axis tensile FRP specimens. The method applies a tensile load to a thin walled tubular specimen through a high strength, small diameter length of steel wire. The low torsional stiffness of the wire allows one end of the tube to rotate, thus preventing any torsional constraint. Analytical and experimental verifications both indicate that the required tensile load can be applied to tubular specimens without significant torsional constraint. The wire based testing method is used to measure the off-axis stiffness properties of carbon/epoxy tubular specimens at a range of fibre orientations.

The objective of this research project has been to develop a computer controlled cyclic simple shear apparatus and to investigate the repeated load behaviour of local basecourse aggregates with regard to their shear modulus and volume change properties. A detailed discussion of the construction of the apparatus and the development of the control systems is presented. A review of the litreature regarding cyclic load testing of basecourse aggregates has been undertaken and presented in this thesis. A large number of shear displacement controlled cyclic simple shear tests were carried out using three types of local Auckland aggregate. A comparison of the performance of these materials is presented with particular emphasis placed on the shear modulus, volume change and particle degredation properties. High repitition cyclic simple shear tests have revealed an apparent stiffness recovery for granular specimens between test runs. This behaviour is difficult to explain, however it is thought to be related to the transition from a dynamic to a static state of friction within the specimen. The volume change properties of granular specimens have been found to be equivalent to the 'normally consolidated - over consolidated' behaviour of fine grained soils. This observation is consistent with that reported by Youd (1970) who performed similar tests using specimens of sand. The implications of this result are discussed with respect to the potential application to highway engineering. A number of shear stress controlled cyclic simple shear tests have been performed to investigate the applicability of a stability threshold for basecourse materials. The stability threshold, or shakedown behaviour, has been observed and is incorporated in a philosophy for pavement design. An example of this method has been performed to show the potential merits of including stability threshold data in the pavement design procedure.

This model study is concerned with attempting to identify some of the mechanics of pile-soil interaction under the influence of static loads, as a pre-requisite to defining the mechanics of the soil response to pile transmitted dynamic (i.e. seismic) lateral soil loads. The emphasis has been directed at the mechanics of the response of the soil to loads transmitted through the pile, rather than the more usual approach of defining an analytical pile model and assuming a soil response. The work contained herein follows the incremental deformations occurring within a soil mass throughout the process of installation through to the ultimate lateral loading condition. To enable this to be done the comparatively recent developments in soil mechanics involving the application of the techniques of stereophotogrammetry and radiography, have been employed. The study is mainly involved with short rigid models in dry dense sand. A more general aim of the research project has been to attempt to draw the more research orientated and practical aspects of the statically loaded pile problem closer together. To this end, state-of –the-art reviews of both the axial and lateral loading situations have been conducted and an attempt made to relate them to the mechanics of soil response, as identified both in this research project and from full scale tests reported in the literature. An attempt has been made to apply some of the more general observations resulting from the study, to the Type A prediction, (i.e. before the event), of the ground line displacements of a full scale pile under real site conditions when subjected to various loads.

Outage probability calculations are presented for the analogue land mobile radio situation where in order to obtain satisfactory radio reception both a sufficient CNR and CIR need to be achieved simultaneously. Such calculations can be used in the design and analysis of mobile radio systems and may be particularly useful for investigating the effects of cochannel interference in cellular systems. The outage probability expressions are derived using previously reported statistical descriptions of mobile radio propagation. Attention is generally focussed on situations where signals suffer Rayleigh fading and/or lognormal shadowing. However calculations for Nakagami-m, Rice and Weibull fading are also considered. The rapid growth in cellular mobile radio systems has stimulated the development of outage probability calculations for multiple interferer situations. Previously, while single interferer situations had been treated exactly, multiple interferers had been treated by approximate methods. In this thesis exact multiple interferer outage probability expressions are presented for the Rayleigh fading and the joint 'fading and shadowing' (Suzuki) situations. Similar expressions, but for more limited cases, are also presented for lognormal and Nakagami-m statistics. Using results from these expressions the accuracies of several approximate outage probability methods are assessed. The exact outage probability expressions for multiple Suzuki interferer situations are closely related to those for multiple Rayleigh interferer situations. Indeed, the exact analytic expressions for Rayleigh statistics form an integral part of the corresponding outage probability expressions for Suzuki statistics. These latter expressions can be readily evaluated using Gauss-Hermite numerical integration. In order to demonstrate the use of such calculations for mobile radio system analysis several theoretical examples are presented. Outage probability calculations for multiple interferer systems which employ diversity reception as a means of improving communications reliability are considered. Similarly, the extension of outage probability concepts to digital systems is briefly outlined.

Local scour at cylindrical bridge piers in both uniform and non-uniform cohesionless sediments was investigated experimentally. The aim of the study was to improve understanding of local scour around bridge piers with sediment transport. Three empirical functions which relate the equilibrium depth of scour with approach velocity, flow depth and sediment size were obtained for uniform sediments. The effects of armouring and sediment sizes were also investigated for non-uniform sediments. The experimental results for the variation of equilibrium scour depth (normalised with the pier diameter) with approach velocity show that the equilibrium scour depth reaches a maximum at the threshold condition of the bed sediment. Above the threshold velocity, the scour depth first decreases and then increases again with increasing velocity to a maximum at the transition flat bed condition. At still higher velocities, the equilibrium scour depth decreases due to the formation of antidunes. Lesser scour depths are recorded with ripple forming sediment at threshold conditions because the bed associated with a ripple forming sediment is unable to remain planar. In live-bed conditions, the effect of rippling diminishes for increasing velocity and becomes negligible for UO/UOC > 2. The experimental results for the variation of equilibrium scour depth with flow depth show that the trend for live-bed scour of increasing scour depth with increasing YO/D until a maximum influence of YO/D is reached, is similar to that for clear water scour as shown by Ettema (1980). A flow depth adjustment factor, K(YO/D), which is related to YO/D with D/d50 as the third parameter is presented which indicates to a designer the sequence of estimation of the effect of flow depth on the equilibrium depth of scour. The effect of sediment size on the eguilibrium scour depth is presented in terms of the relative size of pier to sediment, D/d50. A family of curves, at various values of UO/UOC, which relate dav/D and D/d50 for live-bed scour was obtained. The curves show that the equilibrium scour depth increases almost linearly for increasing values of D/d50 until it reaches the value of D/d50 = 50 after which the scour depth becomes independent of D/d50. A similar trend was obtained by Ettema (1980) for clear water scour. For design purposes, the data for large values of YO/D are presented in terms of a sediment adjustment factor, K(D/d), which is shown to be independent of the flow velocity. Both flow depth and sediment size functions include results by Shen et al (1966), Ettema (1980), Chee (1982), and the present study. Armouring and sediment size play an important role in reducinq the equilibrium scour depth for non-uniform sediments. The latter is particularly significant in laboratory experiments where the size of the pier is generally small relative to the size of the coarse particles in non-uniform sediments. Experiments were conducted under dynamic equilibrium conditions where there is continuous sediment input from upstream of the scour hole such that at equilibrium, the amount of sediment entering the bridge site is equal to that leaving. Both the effects of armouring and sediment size diminish for increasing velocity. At high velocity where all the sediment particles are mobile, the non-uniform sediment behaves like a uniform sediment. Hence, armouring does not occur and the equivalent size used for sediment adjustment is based on the d50 size of the sediment bed. At low velocity, armouring at the base of the scour hole is prominent and adjustment of D/d is based on the d90 size of the original mixture. An alternative condition can exist in natural rivers in contrast to the dynamic equilibrium conditions simulated in this study. This is where the upstream river is armoured such that there is little or no sediment input to the scour hole. It is postulated that, in this case, the equilibrium scour depth can approach the maximum equilibrium scour depth for clear water conditions (i.e. dav/D + 2.3) when the approach velocity is equal to the critical velocity of the non-uniform sediment. Finally, a design flow chart is presented for estimation of the equilibrium depth of local scour for design purposes. In live-bed scour where bed features are present, the results show that half the height of the bed features can be added to the estimated equilibrium scour depth.

This study examines the one dimensional response of sand. For this purpose a compression shear apparatus based on a multi-ring consolidometer has been developed in which one dimensional loading and unloading tests can be performed without wall friction, and in which simple shear distortion of an enclosed sand can be evaluated. The apparatus is also used to examine one dimensional unloading following horizontal shearing of a vertically loaded sample, which is of special interest for one dimensional behaviour in liquefaction associated phenomena. The one dimensional experimental results obtained from this apparatus are modelled using a mechanistic theory proposed by Dr G. R. Martin. In addition, particulate techniques are developed to investigate the underlying mechanisms occurring in the sand. To assist in this investigation special one dimensional, triaxial, and shear tests were performed and use was made of experimental results from published sources.