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A new model for piezoelectric ultrasonic transducers is proposed. Using a systems engineering approach, the concept of feedback is used to explain secondary piezoelectric effects and to clearly describe electro-mechanical interaction. The model is derived from the fundamental piezoelectric equations and it embraces the relevant practical situations where the transducer is subject to arbitrary electrical and mechanical loading. The following main features are incorporated within the model. a - It is valid over a wide range of frequencies, b - It is applicable in both transmission and reception modes, c - It involves realisable elements which are readily simulated, and d - piezoelectric, pressure and voltage interactions are clearly related. The model has been verified extensively in computer simulations and water tank measurements of transducer profiles. Extremely close substantiation of the theoretical analyses was obtained, and the model is considered to offer significant advantages over existing transducer analogies.

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This thesis is concerned with the development and testing of a dynamic simulation program for isolated, compact power systems of the type found in the marine and, off-shore environments. The modelling of electrical machines and their controllers is presented; the modelling of prime movers and governors is considered in detail and representations are proposed for the various driver; and loads encountered in these systems. The significant non-linearities in the systems are fully represented, A test procedure applied to an off-shore system is described and test results are presented. These are compared to simulated results for system and prime, mover responses to validate the simulation procedure adopted. In additions other validation procedures using data supplied by manufacturers are presented. These validation procedures are used to justify the mathematical representations of the, various subsystems and also to validate their co-ordination to form a complete system model. Results for a range of system studies are presented to indicate the range, flexibility and versatility of the overall simulation program.

In this thesis a thorough investigation of 4-reactor shunt compensated systems under unbalanced fault-transient conditions has been carried out. Mathematical models for incorporating 4-reactor compensators into single and multi-section feeder systems, together with the technique used to simulate reactor saturation, are developed. The techniques are very general, are applicable to transposed and untransposed multi-conductor lines of any configuration, and can take into account the frequency dependence of system parameters. Using these techniques computer programs are developed to study : a - Effect of shunt-compensation on primary system response. b - System and reactor overvoltages. c - The probability of reactor saturation and its effect on primary system wave forms and hence on the performance of distance protection. d - Effect of shunt-compensation on the performance of distance protection.

This dissertation is concerned with the improvement of the transient response of turbo-generator sets following a severe system disturbance. The improvement in response is obtained by the application of a single additional system state into the relevant controllers. The system state used is that of rotor acceleration. Theoretical studies are carried out to obtain the feedback gains required for single machine co-ordinate control of excitation and governing. The study is then extended to a multi-machine system. The control laws obtained from the theoretical studies are applied in the laboratory to micromachine systems. A method of obtaining a rotor acceleration feedback control signal is developed and applied to these laboratory micromachine systems. The acceleration transducer forms an essential part of a dedicated microprocessor data acquisition system, which, apart from the functions of data collection and processing, performs a real time simulation of the governor turbine model. The output of this simulation is then used to control the micro-machine prime mover torque. An essential feature of the microprocessor system is the determination of control laws for both the governing and excitations systems during transient conditions.

The synchronous reactances of a salient-pole synchronous machine are functions of the load of the machine because of the non-linearity caused by magnetic saturation. In the d-axis the machine is more saturated than in the q-axis, and for exact analysis appropriate saturated reactances have to be used. A three dimensional numerical solution of the field problem, based on network method is developed to calculate the reactance. The non-linearity of the magnetic materials, the complicated contours of the cross section of the machine, and the currents in the various windings are fully considered. The analysis is applied to the predetermination of flux and flux density in a homopolar linear synchronous machine. The flux densities are used to predict the magnetising inductances, by the use of a flux linkage method. The normal forces acting between the rotor and stator are also calculated in a number of different ways including the use of Maxwell's stress. The field is described and the simplifying assumptions arid boundary conditions are discussed. The governing equations for scalar potential in terms of network properties are developed from Maxwell's equations. The numerical solution of the linear set of network equations is obtained by successive over-relaxation and the nonlinearity is considered by an alternating relaxation procedure. The difficulties associated with the use of scalar potential have been overcome by considering the permeable region to be current free. All the current-carrying conductors are placed in the surrounding air. Equations for a simple air-gap calculation of the inductances and normal forces in a homopolar linear synchronous machine are derived. The leakage inductances produced by air-gap flux which fails to reach the rotor have been considered as parts of the magnetising inductances. Inclusion of these leakage components enables close agreement to be obtained with the measured voltages. The leakage components have no influence on the forces produced by the homopolar LSM. The good agreement achieved in a comparison between the calculated and experimental results for the homopolar linear synchronous motor, confirms the validity and accuracy of the network field calculation method. The mechanical and electrical characteristics of the homopolar LSM are compared with those already found for a heteropolar machine. The advantages and disadvantages of both these machines for advanced transport system are discussed in details. Methods for improvement of power factor and for reducing pole losses are also mentioned.

This thesis investigates the current approach to decision making in the construction industry with its background of uncertainty in relation to such factors as workload, production methods, resource availability and profitability. Given this situation, and the less than deterministic environment that usually surrounds the construction project, effective planning and control procedures are seen as a prime necessity and not as a luxury. Within this context, the most significant decisions relate to the time and cost parameters and more specifically to their interrelationship and the need to provide optimal or near optimal solutions to this relationship. A preliminary feasibility study was conducted in conjunction with six building construction companies operating in the United Kingdom. This indicated that the potential for substantial benefits exist and was further substantiated by replies received to a questionnaire circulated to one hundred additional construction companies. The time and cost parameters are investigated and the related decision problem formulated in a quantitative manner. Existing models are examined and three alternative models are postulated, viz. an integer linear programming model - this model, like the existing models studied, is difficult to implement due to the large number of variables and constraints involved; an integer linear programming model based on breakthrough points on the cost curve (since the number of breakthrough points is less than the number of points of discontinuity, there are fewer integer variables) and a heuristic model capable of dealing with the problems associated with nonlinear time cost curves using a microcomputer. Appropriate programs are developed for use on a CBM 32K microcomputer with a dual drive floppy disk system and high speed printer. Both the integer linear programming models and the heuristic model are tested using simulated project data. Comparative tests indicate that the heuristic model, although adopting a simpler method of analysis, is capable of providing a solution comparable in accuracy with the more sophisticated integer linear programming model. The computer system is designed to permit the data to be structured in several different ways depending on the needs of the recipient, ie., the person who makes the decisions receives only that part of the output that is relevant to their action.