Whole document restricted, see Access Instructions file below for details of how to access the print copy. / Although pinched sluice concentrators have been used for the concentration of heavy minerals for many centuries, their mechanisms involved have not been fully understood. Previous studies on the performance of pinched sluices have been of a purely empirical nature. In the present analysis, an attempt has been made to explain the behaviour of a pinched sluice in terms of the established theories of fluid mechanics and minerals processing. In spite of the inherently complex nature of two phase flow, a method has been developed to calculate the underflow discharge by assuming a logarithmic velocity distribution and free gravity fall through the discharge slot. The concentration profile of solids over the depth of flow has been shown to comply with Bagnold's theory of dispersive shear, rather than turbulent sediment transfer. Even although the results can be explained qualitatively by the Bagnold's theory, their complete quantitative analysis will not be possible until more work is done. Consequently, an empirical equation has been developed to predict underflow pulp densities. The segregation process of the heavier mineral beneath the lighter has been shown to obey a first order law, as was originally proposed by Mayer in relation to jigging. In the light of the results obtained, a computer model of the pinched sluice has been developed. This predicts the underflow grade, pulp density and flow rate in terms of the feed and operating conditions. The model can also be used to determine the effect of a change in operating conditions, and for the optimisation of rougher, cleaner and scavenger circuits.

Reducing oil content, minimizing any carcinogenic acrylamide in the high temperature frying process for potato crisps, and producing good products with considerable crispiness and acceptable color were the objectives of this research. Vacuum frying with pre-treatment of potato crisps was investigated as an effective process for oil content reduction. Pre-drying and subsequent dipping (PSSD) in a sugar solution (‘sugar dipping’) were considered as an advantageous procedure for the treatment of potato crisps before frying in order to reduce oil uptake during frying. Vacuum frying was observed as an excellent process to decrease significantly the acrylamide formation at low temperature frying of potato crisps. In this study, potato crisps were respectively blanched, pre-dried, and dipped in a solution of sugar (23.07 wt %) for two seconds, before vacuum frying at 120oC, 110oC under different vacuum pressures (170mbars, 150mbars, 100mbars and 50mbars in separate experiments). Conventional frying at 180oC was also used as the control to benchmark the reductions in the oil contents and acrylamide formation among various techniques. There was a significant reduction in oil content of the potato crisps observed when the new techniques were applied. The crisps that had been pre-treated and fried with conventional frying have given the result of 30 wt % reduction. The crisps that were fried under vacuum frying achieved greater oil reduction with varying percentages when applying different pretreatments. The lowest oil content was achieved when the potato crisps were fried at 110oC and 150 mbars giving 58 % reduction on the dry basis compared with control samples. There are various advantages of the technique with PSSD as we have discovered: it is simple and can be applied in potato crisp industries in continuous mode in both vacuum and conventional frying systems. The crisps that had been treated with pre-drying and subsequent sugar solution dipping and then fried were crunchier and possibly had better perceived taste to the consumer, due to the small sugar addition. Pre-drying and vacuum frying have all turned out to be excellent techniques to reduce acrylamide formation in potato crisps as we have found in this study. Vacuum frying at 120oC and 150 mbars reduced acrylamide formation by 80 to 85%. The 95% reduction was obtained when the crisps had been pre-dried. Acrylamide was undetectable when crisps were pre-dried and vacuum fried at 110oC, 150 mbars. The crisps with pre-drying subsequent sugar dipping and vacuum fried at low temperature had improved color compared with the control samples, which were produced by conventional frying at high temperatures. / Note: Part 3 publication restricted due to copyright restrictions.

Three phase AC drives controlling cage induction motors have become widely accepted in industry, but one extant problem with this technology is that of increased acoustic noise emitted from the driven motor. This Thesis addresses the problem of the acoustic noise emitted from motors driven from voltage sourced PWM inverters and proposes a technique - Spread Spectrum Switching - for minimizing its effects. In the course of the work many other issues associated with real-time microprocessor-based PWM have also been advanced: • efficient microprocessor based PWM waveform generation, • harmonic analysis of generalized PWM waveforms, • compensation for the effects of power switch timing delays, and • compensation for the finite resolution of timers. The Thesis uses a variety of computational and analytical methods, backed by experimental observations, to quantify the improvement gained in each of these areas. Spread spectrum switching is a technique for eliminating the characteristically tonal structure of the acoustic noise emitted from a PWM inverter driven motor. Similar to the concept of spread spectrum communications, spread spectrum switching involves pseudo-randomly varying the instantaneous PWM switching frequency so that the energy of any PWM switching harmonics is dispersed over a wide bandwidth. This energy dispersion effectively eliminates any tonal components from the resultant motor acoustic noise while leaving the overall sound level largely unchanged; spread spectrum switching provides a significant qualitative yet minimal quantitative noise reduction. The PWM generation paradigm used in this Thesis is the recently reported Space Vector Modulation. A novel algorithm for microprocessor based space vector PWM generation is proposed, providing a basis for fast, efficient generation, even when overmodulating - a situation where many algorithms operate significantly more slowly. Furthermore, it is shown that the space vector method inherently generates a near optimum - in terms of motor harmonic loss - PWM waveform. However, when physically realized on a practical inverter such ideal PWM waveform s are corrupted by timing errors associated with both the inverter's power switches, predominantly the lockout time, and the finite resolution of hardware timers. Resolution corrected modulation is proposed for overcoming the problem of finite timer resolution and involves the use of integral feedback to account for any errors between ideal and physically realizable PWM switching times. This technique effectively provides 4 to 5 bits of added resolution to a given timer, allowing accurate waveform generation at low sinewave amplitudes and high switching frequencies using readily available, often microprocessor based, timers. Lockout times cause inverter output voltage errors, with consequent current zero crossing distortion, and a strategy for alleviating this problem is proposed and implemented in both a triangulation and space vector modulator. Two harmonic analysis techniques are proposed for analyzing PWM waveforms. The first technique is suitable for the analysis of regularly sampled PWM waveforms and has been used here to obtain closed form expressions for the harmonics of both space vector and asymmetrical triangulation PWM. These expressions show that PWM harmonics occur as a series of "combs" centered on multiples of the switching frequency. A second technique - the Directional Rotational Transform - is proposed for numerical analysis of general PWM waveforms. This technique uses an equivalent space vector representation of the PWM waveform, yielding the magnitude, phase and sequence (positive or negative) of the harmonics, and is useful in situations where each of the three phase waveforms is different, as in these cases Fourier Transform analysis of a single phase or line voltage only approximates the harmonics actually seen by the motor. The spectra generated using both these techniques compare favourably with those measured experimentally and, for synchronous PWM, those evaluated from Fourier Transforms. The culmination of modulation techniques presented in this Thesis yields a microprocessor based AC inverter drive featuring low acoustic noise emission at but a few kiloHertz switching rates and accurate PWM waveform generation using a single chip, low cost, micro-controller.

Studies of the families of variable length self-synchronising T-Codes are presented. The studies use Monte Carlo computer simulations to analyse the synchronising properties of the T-Codes and the relationships between these and their coding efficiency. Software and hardware implementations of the algorithms which are used to support these simulations are documented, and one of the encoding/decoding techniques presented is shown to be capable of operating at very high speed while being simple to implement. This technique is also shown to be applicable to the encoding and decoding of any variable length, exhaustive, instantaneous code. From the results of the simulations it is shown that some T-Codes consistently outperform others in the family with respect to their synchronising properties, and that the best of these codes have an average synchronisation delay of approximately 1.5 codewords. More importantly, it is shown that the T-Codes with the best synchronising performance are also the most efficient when encoding symbols from a specified information source, and that the coding efficiency of these codes is only nominally less than that of an optimal Huffman code generated for the source. A theoretical analysis of the synchronising properties is presented, and this is used to explain the relationships which exist between the average synchronisation delay and coding efficiency. These results are used to demonstrate that it is possible to choose a T-Code which has both the desirable properties of unrivalled synchronising performance and optimal coding efficiency, and guide-lines are given for choosing such a T-Code for a specified information source. This combination of a fast and simple encoding/decoding technique with codes which have unrivalled synchronising performance without sacrificing coding efficiency is offered as a solution to many of the problems normally associated with variable length coding techniques.

The work in this thesis investigates the nature of the two dimensional nonlinear seismic ground response of alluvial basins. Computer programs are developed to analyse both the out-of-plane (SH) and in-plane (PSV) two dimensional solution spaces. A finite difference approach is utilised. The seismic input motion may originate from either below or from within the two dimensional mesh modelled. The analyses are performed in terms of total stresses and strains, and pore water pressures are not taken into account. A transmitting boundary allows energy to radiate from the solution space. The computations are performed with a nonlinear soil model which incorporates hysteretic material damping. The shape of the initial loading curve of the soil model may be arbitrary, but the majority of the analyses presented utilise a hyperbolic initial loading curve. Alluvial basins of constant L/H ratio are analysed subject to both vertically propagating seismic waves and seismic waves inclined at angles to the vertical. Both simple displacement pulse and complex transient earthquake acceleration input forms are utilised. Varying levels of excitation are employed to study the effect of strain level on the basin response. Two dimensional basins of varying L/H ratios are analysed subject to vertically propagating waves, and the results compared to a one dimensional nonlinear formulation. The results obtained using a hyperbolic initial loading curve are compared to those produced using initial loading curves derived from empirical relationships for dynamic soil properties. Results from the two dimensional nonlinear analysis are compared to those obtained from a two dimensional linear visco-elastic solution. A detailed case study is investigated with the two dimensional nonlinear analysis forming part of the Ashigara Blind Prediction Test. Elastic closed form solutions for simple two dimensional configurations are calculated, and time domain results compared to the nonlinear analysis. In-plane Rayleigh wave and out-of-plane Love wave characteristics in the nonlinear medium are investigated. A study of soil-structure interaction in the nonlinear medium is made. The feasibility of including discrete fault source models in the two dimensional analysis is investigated, with both dislocation and stress drop methods of input. The two dimensional nonlinear site response analysis method presented in this thesis is found to be a very flexible tool in calculating the ground response of alluvial basins to seismic waves. The method is relatively inexpensive computationally in the light of present computer capabilities. The method is therefore preferred to one dimensional and linear visco-elastic analyses in calculating the response of alluvial basins, given sufficient site data.

This study compares the effects of viscous and coulomb damping on the dynamic response of single and multidegree of freedom structures. It was found that coulomb damping was less effective than viscous damping in reducing the steady-state resonant amplitude of all non-linear structures when the steady-state amplitude was greater than two. Also, there is no single, simple relationship relating the amount of viscous damping to coulomb damping for equal resonant steady-state response of non-linear structures. For the earthquake excitation of the single-degree-of-freedom structure it was found that coulomb damping was less effective than viscous damping in reducing the velocity and displacement spectral response values for short period structures whereas for longer period structures coulomb damping was much more effective than viscous damping. Both forms of damping had a paradoxical effect on the acceleration response of non-linear structures in that an increase in damping generally causes an increase in the acceleration response. The closed solution of a multidegree of freedom structure with viscous and coulomb damping subjected to a sinusoidal forcing function is derived and used to obtain approximate values of viscous and coulomb damping from small amplitude vibration tests. It is clear from the results obtained that if coulomb damping is present in small amplitude vibrations of a structure then the concept of equivalent viscous damping will result in the structure being overdamped when subjected to an earthquake ground motion.

The problem of local scouring at a circular cylinder in sandy material under threshold conditions was investigated experimentally. The aim of the study was to obtain a better understanding of the mechanism causing scour. Three fixed-bed scour models were constructed: the initial flat-bed model, an intermediate scour model and the final equilibrium scour hole model. The experimental results have shown that although scour is initiated by the high local shear stresses which result from flow acceleration about the cylinder, the subsequent development of the scour hole is due to the establishment of a strong downflow ahead of the cylinder. The scour hole grows in the form of a frustrum of an inverted cone at a slope angle equal to the dynamic angle of repose of the bed material. Erosion occurs in the bottom part of the scour hole. Bed particles from the upper part of the hole slide down into the erosion area as the slope angle is increased by erosion of material from below. The equilibrium depth of scour is attained when the downflow becomes incapable of further erosion. For a particular bed material the downflow should be primarily a function of the mean approach flow velocity and cylinder diameter. Hence the study has shown that the equilibrium depth of scour should also be a function of these two parameters. Additional measurements have shown that the horseshoe vortex, which is initially small, roughly circular in cross-section, and comparatively weak, increases dramatically in size and strength as the scour hole forms. During the development of the scour hole, the horseshoe vortex expands and moves down into the hole, increasing its circulation throughout the scour process, but at a diminishing rate. The shape of the vortex follows that of the scour hole-cylinder combination. Measurements in the wake have added to existing information concerning the shedding and convection of wake vortices in shear flow. The results obtained are consistent with the occurence of span-wise cells of constant shedding frequency, separated at the discontinuities by longitudinal vortices. The vortices accelerate away from the cylinder at speeds initially less than the free stream but becoming constant and approximately equal to the free stream velocity at about 8 cylinder diameters downstream. Based upon a survey of existing material, a design recommendation for the estimation of local scour depths at bridge piers is also presented.

The mechanical properties of glassy poly (methyl methacrylate) have been examined by means of constant strain-rate tests at differing strain-rates and temperatures. Both fast-cooled and slow-cooled samples have been examined in order to determine the effect the rate of cooling has upon the mechanical properties. The ß and α’ relaxations were revealed in the experimental results. The difference in mechanical properties of fast- and slow-cooled samples could not be satisfactorily explained by the theory of Rusch.

The purpose of this research is the twofold one of attempting to answer some of the current problems in Engineering Hydrology and at the same time to provide analytical methods for the basic understanding of hydrologic systems. In order to design hydraulic structures such as spillways, dams, bridges, flood control and drainage schemes on a sound economic basis it is essential that accurate statistical data be available for the streamflow under consideration. Obtaining such data are: The two basic methods of (i) Statistical analysis of available streamflow records. (ii) Use of a deterministic catchment model together with statistical rainfall data.

Whole document restricted, see Access Instructions file below for details of how to access the print copy. / The stress-strain and strength properties of a residual soil sampled from the North Shore, Auckland, were investigated through stress and strain-controlled triaxial tests. Emphasis was placed on determining the behavioural characteristics of the soil under conditions of very low effective stress. The soil sampled was a silty clay, derived from the Waitemata Series, with the following average properties: natural water content 45.5%; initial bulk density l707 kg/m3; density of soil particles 2.63 t/m3; plastic limit 32; and liquid limit 60. The peak shearing resistance of the soil was observed to be accurately defined using the Mohr-Coulomb failure criterion, even at very low confining pressures. In addition, the Waitemata clay exhibited a measurable tensile strength of between 7.7 and 12.0 kPa. These results lead to the conclusion that the observed cohesion intercept for the soil could be relied upon for design purposes. The natural variation in void ratio of the Waitemata clay led to the use of total volumetric strain for improved stress-strain correlations. A modified critical state relationship for the soil was subsequently presented, with a unified soil model being used to predict the behaviour of the Waitemata clay. This model demonstrated the ability to replicate the general stress-strain and peak characteristics of the soil. The Waitemata clay did not display the yielding characteristics which are common to residual soils, rather the soil demonstrated continuous yielding behaviour. Anisotropy of the Waitemata clay was also found to be negligible. The use of volumetric strain in the calculation of consolidation properties required only simple modifications to existing consolidation formulae. Bender element tests enabled the small strain shear modulus of the soil to be evaluated. Comparisons of Gmax with the undrained shear strength produced a linear correlation (Gmax =284su) which was significantly lower than expected.