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(1972)ThesisThe formulation of an adequate description of neutron populations in the presence of boiling moderator or coolant is attempted. Starting from a framework of comprehensive stochastic descriptions we concentrate on the special requirements of the boiling system such as the use of transport theory and the retention of heterogeneity in our model. Working equations are derived which show how adequate corrections for boiling can be made to the approximate models currently used. The detailed distribution of bubbles in a boiling system should be accounted for in accurate evaluations of criticality, especially where the bubbles are large. Evaluations of leakage, resonance escape probability and thermal absorption are modified by the detailed bubble distribution. Explicit corrections are given for simple examples, while inclusion of the effects into a practical criticality code, such as WIMS, is discussed. The second moments of the neutron population in the presence of boiling media are also described. The power spectral density arising from the fission process is evaluated, showing how this spectrum is affected by the boiling. Usually more important sources of neutron noise in a boiling reactor are the fluctuations in cross-sections and collision probabilities arising directly from random local void ages. This 'bubble noise' is evaluated with particular emphasis on the detection of onset of boiling in a channel or change in boiling regime. The use of Monte Carlo techniques in calculating neutron transport in boiling media is discussed in some detail. The applicability of the analyses of neutron means and variances to fast reactor situations is considered. The bulk of the work treats critical reactors. However, a treatment of transients and feedback effects is also included. A new analysis is suggested whereby means and variances throughout the transient can be evaluated without extreme difficulty. The concepts of stochastic stability are discussed.
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(1979)ThesisOwing to its excellent vibration isolation capability, the squeeze film damper is finding increasing use in industry, particularly in the gas turbine industry. Design information for squeeze film damper supported flexible rotors has been scarce and has been restricted mainly to small journal orbit eccentricity, and consequently to small unbalance loading. However, unbalance loading can increase in service, resulting in highly undesirable operation modes. This thesis analyses theoretically and experimentally the effect of the relevant system parameters on the possibility of such undesirable operation modes, on unbalance force transmissibilities, on rotor excursion amplitudes and on the orbit stability of squeeze film damper supported flexible rotors, with a view to aid the design of such rotor bearing systems. Assuming Reynolds equation with constant lubricant properties, the short bearing approximation and synchronous symmetric motions, the equations of motion are solved numerically. Rotor excursion amplitude and transmissibility data are presented for a wide range of operating conditions, showing the effect of the system parameters on the responses. It is shown that pressurization of the oil supply is conducive to smooth passage through the first pin-pin critical speed of the rotor. The system stability is investigated for small perturbations from the equilibrium solution (using Routh's criterion) and stability maps are superimposed on the journal eccentricity frequency response plots). Pressurization is shown to stabilize the rotor bearing system and supply pressure data are presented, showing the minimum pressure required to suppress the undesirable operation mode and to ensure stable operation. A theoretical model is developed for optimal fine tuned system design. Optimal support data and the system responses are presented on a single chart for a wide variety of rotors operating under the second bending critical speed. The design and commissioning of the experimental rig and the subsequent experimental investigation to verify the theoretical findings are described in detail. Very good agreement is obtained between theoretical predictions and experimental results. It is concluded that the theoretical model and predictions are valid.
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(1973)ThesisThe problem studied is the finding of the optimum fuel velocity during the approach to equilibrium for a bilaterally, continuously refuelled lattice using natural uranium fuel, as an idealised representation of a natural uranium heavy water pressure tube reactor at constant power. A burnup model is developed from a Green's Function solution of the neutron balance equations incorporating a Legendre polynomial solution of the burnup equation and a pov/er series representation of cross-sections as functions of burnup, and is used to assess strategies suggested by the analysis of simplified versions of the optimal fuel velocity problem. The simplified problems, based on linear dependence of local power and reactivity contributions on burnup, lead to analytical solutions, and are studied as optimal control problems by a discrete version of a continuous gradient optimisation algorithm.
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(1965)ThesisSince the turn of the century a considerable amount of experimental work has been carried out with a view to determining the efficiency with which man converts the fuel energy of his food to mechanical work. From such work, power output figures for extended durations of working have been accumulated, bicycle ergometers being commonly used to load the subject. However, comparatively few studies have been made on man’s ability to generate power for short periods of time e.g. less than five minutes, and little serious attempt has been made to develop a mechanism which would allow, for a given period of time, maximal power release. In the early 1960’s the need for such data was emphasised by workers attempting to design a successful man-powered aircraft. The aim of this work, which is both analytical and experimental in nature, is firstly to develop the design of an ergometer which will allow a subject to work in a wide variety of ways, some of which should allow the release of relatively large amounts of power. The second aim is to carry out an experimental investigation on such an ergometer, to compare the relative effectiveness of various ways of working, and to produce further data on short term man-power output. Chapters 1 to 4 are devoted to a discussion of material which is felt to be of importance in considering the design of an ergometer, and after a survey of some earlier models in Chapter 5> the more important design features of the ergometer which is the subject of the present work, are discussed in Chapter 6. Particular attention has been paid to the loading device, or brake, as it represents an important innovation. Instrumentation and calibration are covered in Chapters 7 and 8, while details of the experimental work are discussed in Chapters 9 and 10. The experimental results show that there are significant differences in the effectiveness of the various modes of working adopted, and that one in particular allowed the production of greater amounts of power up to two minutes, than have been so far recorded and published. The maximum output recorded, over a period of six seconds, was slightly in excess of 2 H.P.