This thesis addresses the problem of analytical determination of the response behaviour of fibre reinforced composite materials, under both quasi-static and dynamic loadings. In the first part of the thesis (Chapters 2 and 3), the effects of microstructural parameters, such as fibre aspect ratio, fibre off-axis angle and fibre volume fraction, on the damping and stiffness of a fibre-composite system are examined. Quasi-static models are, then, developed by using a "Forced Balance Approach" to define mechanical response properties of discontinuous fibre reinforced composite materials. Subsequently, simultaneous optimization of damping, stiffness and weight is carried out by using the so-called "Inverted Utility Function Method". The obtained results show that discontinuous fibre-reinforced composites have superior design flexibility and higher damping properties as compared with those pertaining to continuous fibre-reinforced composites of the same material. In the second part of the thesis (Chapters 4 and 5), the determination of the impact response of laminated composite plates is dealt with. In this context, the "First Shear Deformation Theory (FSDT)" is employed to deal with the so called "Transient Wave Propagation Phenomenon". In this, the "Correspondence Principle" is, then, utilized to extend the obtained elastic solutions to corresponding viscoelastic problems. Here, the closed form displacement solutions are obtained first in the frequency-domain, then, the "Fast Fourier Transformation (FFT)" is applied to invert numerically the dealt-with solutions from frequency-domain to time-domain. The obtained results emphasize the importance of including viscoelastic effects in the analysis, for the prediction of the mechanical response of laminated composites under impact loading.

This study presents a strategy for position feedback control, a so-called self-adjusting adaptive sliding mode controller, to obtain a desired steady state error for a DC-motor servo in the presence of Coulomb friction and stiction. Sliding mode controllers are of the type of nonlinear controllers which have been studied extensively by Russian scientists, including V. I. Utkin and V. Itkis. The self adjusting sliding mode control method that this thesis is focused on is an adaptive discontinuous controller with an approximated sliding mode trajectory. The study is concerned with both analytical and experimental performances of such a class of control strategy and a PID (proportional integral and derivative) controller in the presence of dry friction for the purpose of comparison. The study also investigates the effect of nonlinear phenomenon such as torque saturation on the states of the variables of such a system. The result of the paper is finally based on the suitable performance of the suggested control methodology utilizing a new form of sliding mode controller for the second order class of systems, rather than the conventional forms from V. Itkis and V. I. Utkin.

This research examined three different diving stances during the competitive grab start of swimming--that of the standard position, called the Toes-Over position, the Toes-Back position where the swimmers were not permitted to curl their toes over the edge of the $-$10 degree inclined starting block and the Level position where the platform was levelled. A starting position was being sought which would increase a swimmer's projection angle from the blocks and thus flight time before entry. Eight female swimmers were filmed using a stationary cinecamera while reaction forces were collected, simultaneously, by a force platform mounted on the starting block. Net forces and moments of force at the three leg joints were calculated using inverse dynamics (Winter, 1979). The powers produced by these net moments were then computed to determine which muscle groups contributed to the work done during the start. Based on the results of this study there were no significant differences in the performances of female swimmers using the grab start technique in terms of takeoff velocity, takeoff angle or horizontal distance for the dive when starting from a level surface or $-$10 degree inclined surface. The hip extensor muscles provided the greatest amount of power during the propulsive (thrust) phase of the swim start.

The effects of buoyancy forces on liquid-liquid displacement processes occurring in porous media are important in a variety of practical situations, in particular during the displacement of oil from partially-depleted underground reservoirs by means of aqueous solutions. Most previous studies involving the visualization of water/oil displacements in porous media have been undertaken in horizontal two-dimensional porous medium cells. The objective of this work was to determine the effects of buoyancy forces on the fingering pattern and oil recovery by conducting immiscible displacement experiments in two-dimensional porous medium cells aligned in the vertical plane. A consolidated porous medium cell was utilized to perform the displacements, which permitted a wide range of experiments to be carried out within an identical porous medium. In order to obtain a clear understanding of the effects of buoyancy forces (both favourable and unfavourable) experiments were carried out in three different modes, namely horizontal, vertical upward, and vertical downward. As the effects of buoyancy forces are almost negligible, in the horizontal mode, recoveries obtained in this mode are used as a reference and compared to those obtained in the other two modes. For the system studied in this work, as the displacing liquid in all cases had a higher density than the displaced liquid, buoyancy forces were always favourable in the vertical upward mode and always unfavourable in the vertical downward mode. The immiscible system employed consisted of heavy paraffin oil and glycerol solution as the displaced and displacing phases respectively. The viscosity ratio was varied by changing the concentration of the glycerol solution. Displacements with five different viscosity ratios were studied. Breakthrough time was measured and fractional oil recovery was calculated. The effects of buoyancy, viscous and capillary forces as well as the injection flow rate were also observed. The results obtained indicate that the buoyancy forces are highly effective at very low flow rates and low viscosity ratios (or high density ratios), and even with a slight increase in the flow rate, buoyancy forces lose their importance quickly.

A systematic approach to the free vibration analysis of thin, flat, non-rectangular quadrilateral plates with combinations of simple and clamped supports is presented, using the parallelogram plate as an example. Modifications that Saliba made for the right-triangular plate to the building block superposition method developed by Gorman are implemented. The superposition method is an analytical solution. No simplifications are made to take advantage of the point symmetry of the parallelogram plate, keeping the solution general. The whole plate is divided into two right-triangular and one rectangular segment. Rectangular building blocks are superimposed for each of the segments to meet the required net boundary conditions and the conditions of continuity along the segment interfaces. The Levy-type solution to the eight building blocks used are given, along with the necessary Fourier expansions and a comprehensive guide to assembling the eigenvalue matrix. Numerical results for a wide variety of plates are presented, including numerous mesh and contour plots. Comparison is made to previously published data. The results for the fully clamped parallelogram plate are supported by experimental results. Six aluminum plates were tested for the first six resonance frequencies and the first three mode shapes. Details of the simple, yet highly accurate experimental method are included.

This study evaluated the ability of two different methods of measuring mechanical work, absolute power (AP) and absolute work (AW), to distinguish between normal and impaired gait. The relation between these two measures was examined as well as their relation to oxygen consumption. Global work measures from all three were compared and, in the case of the absolute power method individual joint power curves of the ankle, knee and hip, for normal and two impaired conditions were examined. Four subjects of each gender were examined for one full gait cycle, by three video cameras, over two AMTI force platforms, under three conditions; normal, locked knee and locked ankle. Oxygen consumption was measured with a TEEM 100 unit carried by the subject in a "fanny" pack. Five normal gait and one trial of each impaired condition were analysed. (Abstract shortened by UMI.)

During the hot-rolling of aluminium ingot into sheet, the material elongates in the rolling direction as it is reduced vertically. The spread which occurs in the lateral direction during the multiple pass schedules used in industry is minimal. However, the deformation on these edges is important. During the initial passes a concave profile develops - the material near the surfaces spreads outward while the material at the centre moves inward. The concave profile can lead to defects in the final product; these are the 'roll over' of material from the edges to the top and bottom surfaces, the fold over of material in the centre of the edge, and the formation of vertical edge cracks. To remove these the edges are trimmed at the end of the process. Research work in this area was motivated by the possibility of identifying means of reducing the amount of material that needs to be trimmed. The objectives of this thesis are to develop techniques of simulating the rolling, and to use these to investigate the deformation mechanisms which lead to the concave edge profile. Models of the rolling were developed using the general purpose, non-linear finite element code ABAQUS. To reproduce the edge profiles accurately requires large three-dimensional models, for which the explicit dynamic method was found to be the most suitable. The results of the analyses were used to investigate the mechanisms which lead to the concave edge profile. In the roll-gap the work-load arches through the ingot; and for roll passes with small reductions a stress pattern occurs which leads to the concave edge profile. In this pattern the stresses of highest magnitude at the surfaces are compressive stresses in the vertical direction, while in the centre of the ingot they are orientated in the rolling direction and are tensile. Thus deformation occurs by vertical compression near the surfaces, and by stretching in the rolling direction at the centre. At the edges the material is not constrained laterally; and due to the Poisson effect, the material spreads outward near the surfaces, and moves inward at the centre. The effect of certain variables on the edge profile were investigated with the modelling. The friction between the work-rolls and the ingot was found to have significant influence on the amount of lateral surface spread. Work hardening, strain rate and temperature effects in the material lead to variations in the yield stress through the height of the ingot. These effects were included in the modelling and were found to affect the shape of the profile, but to a lesser extent than the friction.

The novel Balanced Beam Tube Viscometer (BBTV), developed at the University of Cape Town, has been further developed and refined. Extensive work has been done in the following areas: (i) The effective length of the BBTV tubes. (ii) Interpretation of the data obtained using the BBTV in both the laminar and turbulent flow regimes. (iii) Comparison with the rotary type viscometer. Kaolin clay and uranium tailings slimes slurries of different particle size range and concentration have been successfully characterised by yield- pseudoplastic rheologies using the BBTV. The BBTV is in fact a miniature pipeline and it has been shown that it is capable of producing valid turbulent flow data and indicating the laminar/turbulent transition region in the two tube sizes .

Bibliography: pages 132-135. / In deriving asymptotic error estimates for a conforming finite element analyses of static thin elastic shell problems, the French mathematician Ciarlet (1976) proposed an approach to the formulation of such problems. The formulation he uses is based on classical shell theory making use of Kirchhoff-Koiter assumptions. The shell problem is posed in two-dimensional space to which the real problem, in three-dimensional space, is related by a mapping of the domain of the problem to the shell mid-surface. The finite element approximation is formulated in terms of the covariant components of the shell mid-surface displacement field. In this study, Ciarlet's formulation is extended to include the eigenvalue problem for the shell. In addition to this, the aim of the study is to obtain some indication of how well this approach might be expected to work in practice. The conforming finite element approximation of both the static and eigenvalue problems are implemented. Particular attention is paid to allowing generality of the shell surface geometry through the use of an approximate mapping. The use of different integration rules, in-plane displacement component interpolation schemes and approximate geometry schemes are investigated. Results are presented for shells of different geometries for both static and eigenvalue analyses; these are compared with independently obtained results.

No description available.