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.

This thesis presents a theoretical basis and the practical implications for using small-scale (up to 50 kW) low-cost power generating systems comprising an ungoverned turbine, a three phase self-excited induction generator, a variable VAr source for voltage regulation, and an electronic load governor. The thrust of this work is towards the reduction of cost by replacing the more conventional synchronous generator by an induction machine and, by eliminating the site-specific fully-governed turbine. An electronic load governor, utilising zero-voltage switching to minimise waveform distortion, is used to regulate the system frequency by controlling the generator loading. The performance of the load governor is analysed in conjunction with both synchronous and induction generators, and the conditions under which the governed system is stable are determined. The induction machine is shown to have better operating characteristics than the synchronous machine and has the further advantages of low maintenance and ready availability making it particularly suitable for isolated applications. A theoretical explanation of the process by which an induction machine self-excites when capacitance is connected across its terminals is developed, and methods of guaranteeing excitation are proposed. It is shown that the remanent magnetism, present in the rotor, plays a significant role in the machine excitation and the conditions leading to loss of remanence are investigated. Once excited, the operation of the induction generator is analysed for both balanced and unbalanced loadings. The practical implications of these results are taken into account in proposals for single phase supplies, these being more desirable in smaller systems. A range of static VAr sources, including a switched capacitor VAr source and an inductively loaded ac-to-dc converter, are considered for controlling the machine’s excitation. The VAr sources are compared on the basis of harmonic distortion and system stability. The thesis considers the application of these devices to micro-hydro and wind generating systems. Preliminary investigations have been carried out into the use of two-speed induction machines to improve the efficiency of CSCF Constant Speed Constant Frequency wind generating schemes and into the use of centrifugal pumps as ungoverned turbines. Practical results obtained from laboratory experiments and tests on existing micro-hydro installations are included. It is shown that significant reductions in cost are obtainable by employing the methods discussed in this thesis. The resultant systems may incur a reduction in efficiency but there is little reduction in performance and in many respects the quality of supply is improved.

Digitised pictures have both cosmetic and scientific image aspects. This thesis presents an image coding system that compresses monochromatic digital image information in such a way that the cosmetic-or viewed-image aspects of a reconstructed picture are indistinguishable from the original to a (human) observer. The coding system is concerned with viewed aspects of digitised images and is based on a simplified 2-channel model of the human eye, with the image information being separated into slowly varying texture information and rapidly changing edge information corresponding to those two channels. Each of the two types of image data is coded using techniques suited to its individual characteristics. Texture information is coded using predictive waveform coding where the predictive filter coefficients are generated by linear predictive coding (LPC) techniques. Since the waveform prediction is not perfect, this thesis evaluates several different methods of differential pulse code modulation (DPCM) coding the residual prediction error. This signal is then used to improve the texture coding quality. Image edges are isolated from the digital image data by an asymptotically optimal edge detector known as the Laplacian of Gaussian (LOG) filter. Using two image edge models, the LOG isolated edges produce contours which are used to define edge position, shape, and "sharpness". The edge position data is then compressed using a chain-coding system. The thesis also considers the effect the edge characteristics have on the coding system and develops two methods for reducing the number of coded edges. Reconstruction of the coded image is in two parts corresponding to the two channels of the coding system. The texture information is reconstructed by predicting texture pixels and adding the decoded DPCM error signal. Edge information not contained in the texture coding channel is reconstructed using only edge information corresponding to the high spatial frequency channels of the human eye. These two channels are added together producing the final coded image reconstruction. Also considered are the effects of varying the original image sampling density. The 2-channel coding system is applicable to a wide variety of images, producing coded images with a high visual quality and coding bitrates as low as 0.6 bits/pixel (256 x 256 pixel images), while maintaining a relatively low computational overhead both at the encoder and the decoder.

In the 1950's and early 1960's a considerable amount of effort was devoted by Dr. H.A. Whale and others at the Seagrove Radio Research Station (now the Radio Research Centre, University of Auckland), to the examination of some of the problems involved in HF radio propagation. Among these were the evaluation of the effects of large-scale ionospheric tilts, the scattering which occurs at the earth and ionosphere, and the measurement and prediction of incoming bearing and elevation angles of signals from distant stations. In the latter stages of this work it became obvious that little was known about effects occurring at antipodal distances, so attempts were made to examine these and to postulate a propagation model consistent with the effects observed. The results presented in this thesis are a logical extension of this early work, and comprise investigations in three main areas: (1) The shape and size of the antipodal focussing area, (2) The development of a more general and less idealised propagation model, (3) The shape of the incoming angular power spectrum at antipodal distances. A summary of the theory and experimental results contained in chapters 4, 5, 6 and 7 has been published (Bold, 1969), and that contained in chapters 8 and 9 will be submitted for publication shortly.

Networked control systems (NCSs) are a type of distributed control systems where sensors, actuators, and controllers are interconnected through a communication network. This system setup has the advantage of low cost, °exibility, and less wiring, but it also inevitably invites some delays and data loss into the design procedure. The focus of this thesis is to address the problem of analysis and design of networked control systems when the communication delays are varying in a random fashion. This random feature of the time delays is typical for commercially used networks, such as a DeviceNet (which is a controller area network (CAN)) and Ethernet network. Models for communication network delays are ¯rst developed, in which Markov processes are used to model these random network-induced delays. Based on such models, we establish novel methodologies for stability analysis, control with disturbance attenuation, and fault estimation for a class of uncertain linear/nonlinear uncertain NCSs with random communication network-induced delays in both sensor-to-controller and controller-to- actuator channels. Data packet dropouts in the communication channels also have been taken into consideration in the modelling and design procedure. The main technique used in this thesis is based on the Lyapunov-Razumikhin method, which results in delay-dependent controllers. We ¯rst consider the design prob- lems for uncertain linear NCSs. In this case, state feedback controllers and dynamic output feedback controllers are designed to satisfy both stability and disturbance at- tenuation requirements for this class of NCSs. Moreover, a robust fault estimator that ensures the fault estimation error is less than a prescribed performance level is designed. We further go on to address the control problems for uncertain nonlinear NCSs. The nonlinear plant is ¯rst described by the T-S fuzzy model. Based on this model, stability analysis, disturbance attenuation, and fault estimation problems are studied for uncer- tain nonlinear NCSs. It should be noted that system uncertainties, disturbances and noises are addressed in both cases. The existence of such controllers and fault estimators are given in terms of the solvability of bilinear matrix inequalities. Iterative algorithms are proposed to change this non-convex problem into quasi-convex optimization problems, which can be solved e®ectively by available mathematical tools. Finally, to demonstrate the e®ectiveness and advantages of the proposed design methodologies in this thesis, numerical examples are given in each designed control systems. The simulation results show that the proposed design methodologies can achieve the prescribed performance requirements.

The aim of this thesis is the development of an understanding of some of the Limitations involved in the design of active filters. This introduces the idea of imposing an upper bound on the amplitude of the input voltage to an active filter such that the distortion, introduced, in the input stage of the operational amplifier, is Less then a value specified in the design, and investigating theoretically the errors in the frequency response of the actual circuit, caused by the operational amplifier which is considered linear but nonideal in that the analysis includes the finite input impedance and output conductance as well as the single-pole rolloff characteristic. The results of this theoretical research have been incorporated into a package of highly interactive computer programs, collectively called the Active Filter synthesis program, for the design of minimum-phase lowpass, highpass, bandpass, and bandstop active filters, the group-delay equalization of these filters and also of both unloaded, and loaded telephone Lines, and the displaying of their ideal frequency responses. The above-mentioned research arose from the design and construction of an experimental 600/1200 Baud, Modem, the filters in which provide a practical application of these developments. / Whole document restricted, but available by request, use the feedback form to request access.

This thesis describes the design and application of a virtual reality simulator for orthopaedic surgeryof the proximal femur. The aim of the research was to create a simulator with the followingattributes; could be used within the current public hospital setting, reflected the perceived needs ofthe local orthopaedic community, provided surgically relevant feedback about aspects of technicalability to orthopaedic surgical trainees and the training committee, allowed practice of operativetasks which for reasons of radiation exposure could otherwise not occur, was validated, and couldbe developed further for other operations. The ultimate aim of the simulator is to allow trainees topractice aspects of surgical treatment such that their care of real patients is improved. The novel aspect of this work has been the development of a simulator which allows the trainee toperform all the steps required for two surgical procedures; namely hip fracture fixation and pinningof slipped femoral capital epiphyses. The simulator runs on the computers found within the publichospital as it does not require expensive hardware such as haptic (force feedback) devices. Resultsfrom the simulator mimic real world measurements which are seldom available to trainees asfeedback to enable them to practice their craft. A survey of the New Zealand orthopaedic surgeons and advanced trainees showed this communitywas generally supportive of simulation, though only 4 respondents had previous experience with asurgical simulator. The task of practicing angulation/spatial orientation was thought most suitablefor simulation, which is the task which the simulator specifically allows trainees to practice. Morerecently qualified surgeons were more likely to agree that simulation was an effective way topractice surgical procedures. Validation of the simulator was tested in two experiments. The simulator was shown to have facevalidity; i.e. a realistic representation of the operating room. This result was obtained by surveyingusers who had completed a number of virtual operations. Construct validity was assessed by thesimulator’s ability to identify between groups of users with differing levels of real surgicalexperience. The simulator was able to discriminate medical students from orthopaedic trainees,despite the medical students’ greater ability in computer-gaming. Advanced trainees generallyperformed better than basic trainees, though in the limited number of trainees available significancewas not reached. Finally the simulator was developed further to allow all advanced trainees within New Zealand tocomplete virtual pin placement of a slipped capital femoral epiphysis. This demonstrated thefeasibility of using the simulator for assessment of trainees within their normal training weekend. Italso revealed different operating styles, and showed how these differing styles do not correlate withthe accuracy with which the final screw is placed.

This thesis presents the results of developing road pavement deterioration models for the State Highway network in New Zealand pavement deterioration models are an integral part of pavement management systems, which are used to forecast long-term maintenance needs and funding requirements on a road network. As part of this research, a Long-term Pavement Performance (LTPP) programme has been established on 63 sections of the State Highways. These sections are representative of typical road sections and climatic conditions on New Zealand roads. Data collection on these sections is undertaken on an annual basis and consists of high accuracy manual measurements. These measurements include road roughness, rutting, visual defect identification and strength testing with a Falling Weight Deflectometer. Based on the LTPP data, new model formats for New Zealand conditions were developed including a crack initiation model and a three-stage rut progression model. The rut progression model consists of three stages, initial densification, stable rut growth and a probabilistic model to predict accelerated rut progression. The continuous probabilistic model developed predicts the initiation of pavement failure events such as crack initiation and accelerated rutting. It has been found that this model type has a strong agreement with actual pavement behaviour as it recognises a distribution of failure on roads rather than failure occurring at an particular point in time, namely, a year. The modelling of rut progression in the three stages including, initial densification, stable rut progression and accelerated rutting has resulted in a significant increased understanding of this defect, especially for thin flexible chip seal pavements. It has been established that the in-service performance of these pavements is relatively predictable. However, incorporating both the in-service performance and the failure of pavements into one model was unrealistic. Therefore, by having the different stages of rutting, resulted into a more accurate forecasting of this defect. Although this research has covered the two priority pavement models including cracking and rutting prediction, it has established the model framework for other pavement models to be developed. As more data become available, further work can be undertaken to refine the models and to extend the research into the performance of alternative construction materials.

An efficient finite element method is developed to model the spreading of excitation in ventricular myocardium by treating the thin region of rapidly depolarizing tissue as a propagating wavefront. The model is used to investigate the excitation sequence in the full canine ventricular myocardium. The solution to an eikonal–curvature equation for excitation time is shown to satisfy a reaction–diffusion equation for the bidomain myocardial model at the wavefront, while the solution to an eikonal–diffusion equation approximately satisfies the reaction–diffusion equation in the vicinity of the wavefront. The features of these two eikonal equations are discussed. A Petrov–Galerkin finite element method with cubic Hermite elements is developed to solve the eikonal–diffusion equation. The oscillatory errors seen when using the Galerkin weighted residual method with high mesh Péclet numbers are avoided by supplementing the Galerkin weights with C⁰ continuous functions based on derivatives of the interpolation functions. The ratio of the Galerkin and supplementary weights is a function of the Péclet number such that, for one-dimensional propagation, the error in the solution is within a small constant factor of the optimal error achievable in the trial space. An additional noinflow boundary term is developed to prevent spurious excitation initiating on the boundary. The need for discretization in time is avoided by using a continuation method to gradually introduce the non-linear term of the governing equation. A small amount of artificial diffusion is sometimes necessary. Simulations of excitation are performed using a model of the anisotropic canine ventricular myocardium with 23.55 degrees of freedom for the dependent variable, and results are compared with reported experimental observations. When it was assumed that Purkinje fibres influence propagation only on the endocardial surface, excitation of the entire myocardium was completed in 56 ms. Altering material parameters to represent penetration of the Purkinje fibres beneath the left endocardial surface reduced the completion time to 48 ms. Modelling the effects of the laminar structure of myocardium by reducing the propagation speed by 40% in the direction normal to the layers delayed completion of excitation by only 4%.