The drag of backward-facing steps was experimentally measured in a series of turbulent boundary layer flows and in a laminar flow. The main objective of the investigation was to study the influence of the freestream pressure gradients on the drag values for backward-facing steps in turbulent boundary layer flows. The measured boundary layer characteristics of all the established flows are in very good agreement with other published results and their two-dimensionality was ascertained. Two different techniques have been used to measure the drag of such steps. The momentum thickness technique was not suitable for determining the drag of such small irregularities, since the incremental increase in the momentum thickness due to the irregularities was small and the method of calculation was crude. The pressure distribution technique was found to be a more suitable method of estimating this drag. When applied appropriately the measurement uncertainty was small. The drag results published by Gaudet and Johnson for backward-facing steps in a zero-pressure gradient have been considerably extended for a number of turbulent boundary layer flows with values of pressure gradient parameter, a, from -0.97 X 10-3 to 9.14 X 10-3. For small steps results covered a range of irregularity Reynolds number of 150 to 900. For large steps in zero-pressure gradient flow this range was increased up to 3500, and up to 2000 in a mild adverse pressure gradient flow. The drags of backward-facing steps in a laminar boundary layer flow on a flat plate have been measured by the pressure distribution technique. No correlation was made for the drag of such steps in the laminar boundary layer, however a comparison between the total drag of the plate with and without the largest step showed that the total drag of the plate increased by only some 65 % of the clean surface drag value.

Intermediate diaphragms are invariably included in the design of overhead travelling crane box-girders. This study concerns the influence of these diaphragms and their spacing on the global characteristic behaviour of the girder. In particular the action of internal diaphragms in the control of stresses associated with distortional deformation is investigated. The details and results of experimental tests on scale models of two crane geometries are presented. A method of analysis is developed to describe the distortional deformation of crane box-girder geometries using discrete box section elements. This method is assessed by comparison with both the experimental results and finite element analysis conducted for a range of configurations. It is shown to produce adequate predictions for use in further investigations. The theory is applied (by means of computer analysis of different crane box arrangements) to perform a study of the influence of intermediate diaphragms on both transverse distortional bending and longitudinal distortional warping. The results of this study are then incorperated into a series of design recommendations for the selection of cross section geometry and the positioning of diaphragms with particular reference to the control of these distortional effects.

The main question raised in this study is that of whether under conditions of colonial domination, underdevelopment and integration into the world capitalist system there was a possibility for the emergence of a working class in Algeria. This study has shown that the conditions for the emergence and development of a working class existed in Algeria since the colonial period. In this early period the processes of pauperization and proletarianization of large sections of the population through land expropriation and destruction of crafts and local communities have led to the formation of the first groups of wage labour on colonial farms and enterprises. However, the process of working class formation was hindered by the uneven development of colonial capitalism, political repression, racial discrimination as well as internal cleavages based on ethnicity and religion. The post-independence period provided new possibilities for the process of working class formation yet it has, at the same time, revealed its limitations. These were related to the weakness of the working class and the hostile political and economic environment. The experience of Self-management and the struggles which developed around it highlighted the extent to which specific historical conditions have affected working class formation. However, a new impetus to this process was provided by the rapid and intensive process of industrialization. The working class-in-formation not only saw its size expanding may times over in a short period of time (1966-82), becoming one of the main social groupings in the Algerian social structure, but has also acquired a rich and varied experience through its struggles. Despite many unfavourable conditions such as, recency of industrialization, disorganization, subordination of unions, and continued influence of traditional structures the Algerian industrial workers have developed embryonic forms of class consciousness expressing their common identity and shared interests. They have also shown an awareness of societal division and cleavages based on an unequal access to resources, generating antagonisms and conflicts. Most importantly, a majority among workers developed positive orientations toward collective forms of resistance and were prepared given the "right" conditions to engage in forms of collective action. Although expressed views on radical forms of resistance such as strikes, were not too favourable, these must be understood in the historical and situational context of the time. Overall, Algerian workers despite differences relating to the environment, working conditions and management policies, have shown a great deal of cohesion and homogeneity. New conditions have emerged recently following the collapse of the one-party state, an achievement for which part of the credit, at least, must go to the Algerian workers. These emergent conditions offer the working class new possibilities for an autonomous development leading to the realization of its potentialities as a major force in the Algerian social structure.

No description available.

The high latitude ionosphere forms a highly dynamic and disturbed medium which can severely degrade the performance of hf radio links. Characteristics of the signal which may be affected include signal strength, fading rate and the frequency range over which signals may propagate. Furthermore, large Doppler frequency shifts and spreads may be imposed on the signal due to movements in the ionosphere near to the reflection point. To investigate these effects, signals from a transmitter located at Clyde River on Baffin Island in the Canadian North West Territories were received near Fairbanks, Alaska and at Alert, Elsmere Island. Doppler spread, signalling error rates and error distribution patterns occurring were measured during one month campaigns in summer 1988 and winter 1989. Several interesting features were observed: (a) Large Doppler spreads, often in excess of 10 Hz were frequently observed on the trans-auroral path and their occurrence was well correlated with the average position of the auroral oval relative to the path reflection points. (b) The bit error rate of low speed FSK signals was not influenced by the level of Doppler spreading observed. Error rate was well correlated with the received signal to noise ratio and was in good agreement with theory. Signal to noise ratio was well correlated with predicted variations in ionisation due to changes in solar zenith angle. (c) Distribution of errors were related to changes in Doppler spreading. Large Doppler spreads, were correlated with significantly shorter bursts of error was less than when Doppler spreading was small. However, there was no significant correlation with the length of guard space between errors. This work is of particular relevance to researchers developing high latitude prediction programs and those employing channel simulators to assess communication systems.

This thesis considers the use of variable structure and H-infinity control system designs for the improvement of the handling qualities of the Lynx helicopter, with full flight envelope operation and enhanced turbulence rejection capabilities. A model-following variable structure controller is designed, where the 'ideal model' was designed in four different ways using the following methods: eigenstructure assignment, Hinfinity minimum entropy, Hinfinity one degree-of-freedom loop shaping, and Hinfinity two degrees-of-freedom loop shaping. The combination of the ideal model and the loop shaping is seen to allow the time and frequency domain objectives to be specified during the variable structure control system design. The decomposition of the Hinfinity one degree-of-freedom and two degrees-of-freedom control laws into state-feedback and observer form allows the use of these observers in the implementation of the variable structure controllers. Extensive testing and evaluating of handling qualities, throughout the operating flight envelope, is performed on the non-linear Rationalised Helicopter Model. Successful Advanced Flight Simulator trials performed at the Defence Research Agency are described, which signify the first real-time 'flight' of a helicopter controlled by a variable structure control law design. A variable structure observer is designed to complete the variable structure observer/controller framework, and shows good handling qualities and time response characteristics throughout the flight envelope. A novel method of combining established Hinfinity control system design procedures with modelling of the turbulence entering the linearised system equations, enables generic Hinfinity control law designs with significantly enhanced turbulence rejection qualities to be successfully demonstrated. The turbulence effects are modelled as perturbing the helicopter's velocity equations, and are included as an extra input to the Hinfinity Standard Compensation Configuration. Therefore, no statistical knowledge of the turbulence was required. The variable structure control law designs are tested for their turbulence rejection capabilities, and exhibit high levels of handling qualities without having been designed explicitly for turbulence rejection in the design procedure.

The current state-of-the-art of in-vivo optical fibre sensors is reviewed. There then follows a review of techniques for pressure measurement and for diagnosis of obstructive sleep apnoea syndrome (OSAS). A catheter containing seven optical fibre pressure transducers for use in the diagnosis of OSAS is described which has been designed, modelled, built and successfully tested both in the laboratory and on six subjects. The transducer has a range of +/-5kPa, a resolution of 10Pa and a potential bandwidth of >1kHz. Oral and nasal breathing, snoring, peristalsis and airway collapse were distinguished using the system. After a review of angioplasty techniques and subsequent healing or arterial restenosis (AR), another optical fibre sensor is described which was designed and built for monitoring the healing of the endothelium and for the detection of AR following percutaneous transluminal coronary angioplasty. The sensor used a fluorescent antibody antigen reaction and its potential was successfully demonstrated both in-vitro and using mammalian models. The resolution was better than 107p Moles of antibody. It was shown that the use of a similar radio-labelled reaction was not feasible for in-vivo use. The study concludes that there is significant scope for development of optical fibre in-vivo physical sensors and biosensors.

This thesis considers several important issues in the implementation of an expert system for robust controller design. The work focuses on the architecture of the expert system, robust controller design methods, implementation of knowledge bases and issues concerning the integration of these to form a useful robust controller design environment. The main contribution of this thesis is the development of an expert system package to support industrial control engineers in solving their controller design problems. The expert system captures the experiences and skills of human experts, leaving the user of the expert system free to concentrate more on the creative aspects of the controller design. The expert system makes use of recent results on the Hinfinity loop-shaping design procedure (LSDP) of McFarlane and Glover. A two degree of freedom loop-shaping design procedure (TDF-LSDP) of Limebeer and co-workers is also considered to enhance the capability of the expert system. Based on these two LSDP approaches, a systematic controller design procedure has been developed in the expert system for tackling generic control system problems. In addition, the relationships between the closed-loop time/frequency domain performance specifications and the open-loop singular value requirements were also considered. Methods for performing systematic loop shaping design based on the closed-loop time/frequency domain specifcations are incorporated into rule knowledge bases of the expert system. The organization and handling of control related data by a frame system are explicitly described. Several numerical optimization techniques are also examined and incorporated to enhance the robust control system design approach used in the integrated environment. A systematic controller design procedure using Multi-Objective Genetic Algorithm is presented. A Multi-Layer Multi-Objective Genetic Algortihm is developed for designing controllers with varying structures. A number of case studies are carried out to demonstrate the feasibility of the expert system package.

Modern industrial applications often employ embedded processors – programmed with dedicated software – to perform some tasks in real time. In many such designs, the software running on the processor is developed according to rigorous industry standards. Even with such state-of-the art designs, problems can occur “in the field” due to unforeseen circumstances – such as electromagnetic interference – that could undermine the underlying assumptions made at design time. It therefore remains essential to monitor the system at run-time, in order to detect any deviations from the required system behaviour. However, monitoring embedded systems is a far from trivial process, not least because such systems are becoming increasingly complex. Also, variations in task execution times are likely to occur, and can have negative impacts on system predictability particularly in the presence of jitter-sensitive tasks. In addition, it is rarely possible (or cost-effective) to add precise monitoring capabilities to a system which has not been developed from the outset with such requirements in mind. The work described in this thesis seeks to address these issues by introducing and evaluating a “predictable time-triggered” (pTT) framework that combines: a pTT scheduling algorithm and a hardware-based pTT monitor. A novel jitter-reduction technique in a pTT algorithm allows jitter-sensitive tasks to be executed in constant periods without the need to re-compute the entire task schedule. The studies reported in this thesis show that, with existing jitter-reduction methodologies, a pTT algorithm can provide extremely predictable temporal behaviour. The studies also show that the novel low-cost pTT monitor – that operates by monitoring fluctuations in the processor power consumption through a simple hardware interface – adds an additional level of safety by allowing run-time errors to be detected at a time resolution of microseconds. These findings provide sufficient evidence that the pTT framework could be an appropriate model for safety-critical system design.

Following theoretical and experimental studies of multi-axial creep fracture with particular reference to the behaviour of copper at 250°C, a polycrystalline model simulating grain boundary cavitation is examined. In the model, a modified form of Kachanov's damage concept is combined with the Hull and Rimmer vacancy diffusion mechanism to yield a novel rate equation that is critically sensitive to the spacing between cavities. Adoption of various relationships between spacing and applied stress is shown to permit prediction of various stress criteria for creep failure time. The model also incorporates equations expressing the equilibrium of forces at grain boundaries, and compatibility of the displacements arising from mass transfer at cavities. With the aid of numerical integration, these equations show the model behaviour to be relatively insensitive to grain geometry, material properties, and initial and final states of damage, although marked changes in grain shape or ultimate strength can significantly change fracture times. Experimentally, fracture times for copper tested at 250°C in uniaxial tension, biaxial tension and torsion (tube and disc specimens) are found to be a power function of maximum principal applied stress. Model simulation of these fracture times is demonstrated on the adoption of a simple expression, relating void spacing to maximum principal applied stress, suggested by metallographic examination of tapered tensile specimens subsequent to creep tests. Apart from wide variations observed in the damage at any given stage of creep, the main microstructural features of cavitation under steady load are also well simulated. For prediction, the spacing-stress relationship is found inadequate on two counts: it cannot be independently determined by metallo-graphic techniques with sufficient accuracy, and it is inconsistent with the behaviour of tensile specimens briefly preloaded at twice the creep stress.