Browsing by Author "Hennessy, Thomas Richard"

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    Characteristics of ocean gravity waves off the Cape South West coast
    (1974) Shillington, Frank Alan; Harris, T F W; Hennessy, Thomas Richard
    Ocean gravity waves have been recorded near Melkbosstrand with a Wemelsfelder float type wave recorder on a sea tower situated in water 13m deep and one Kilometre offshore. The half hour records, taken twice daily between July 1972 - June 1973, have been analysed in a format uniform with that of Draper (1966). Measurements have been made from the wave records to check the value of the statistical ratios of Longuet- Higgins (1952) and Draper (1963). Ratios of maximum wave height to root mean square amplitude are lower than the theoretical values and reasons for this are discussed in the light of the records being taken in shallow water. Ratios of maximum wave height to the average upper one tenth wave height and average upper one third wave height agree closely with the theoretical values. Spectral analysis using the methods of Blackman and Tukey (1958), with 36 degrees of freedom and 100 lags have been applied to half hour records digitized once per second. Frequency, time diagrams contoured at equal energy values have been constructed for the period May and part of June 1973 on the basis of twice daily spectral measurements at 5 mHz intervals. The wave events, which include generation of swell from near South Georgia, (54°S, 37°W), have been compared with the South African Weather Bureau synoptic charts in order to identify generation centres. Repeated energy values near the 50 mHz band seem to be generated by winds of a lower velocity than required by Moskowitz (1964). Predominant siting of fetches at distances of the order of 1000 nautical miles accounts for the bulk of wave generation between latitudes 40° - 50°S. One storm appears to have originated near the Drake passage, but no events have been detected with waves passing through the passage. Analysis of wave spectra from several storms generating maximum wave heights over 5 metres, show that fully developed seas are seldom, if ever, present in Cape waters.
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    New mathematical models of inert gas transport through biological tissue in hyperbaric environments
    (1973) Hennessy, Thomas Richard; Brundrit, Geoff; Van Zyl, J J W
    The thesis is concerned with a fundamental mathematical analysis of inert gas transport through biological tissue at a raised ambient partial pressure. Three basic time-scales of transport in tissue are defined and their relationship examined and compared with existing models, which e.re shown to be usually inadequate in one or more ways. As a result three new mathematical models are proposed and solved both asymptotically and numerically. The first is applied to experimental data for non-perfused tissue which yields an improved value of the intracellular diffusion coefficient for nitrogen. An expression is also derived which should be useful in evaluating this constant and the volume fraction of extracellular fluid. The second embraces a number of current models and is applicable to perfused tissue. It should be useful in interpreting inert gas uptake curves. The model is applied to experimental data, and a source of possible error is discovered in using experimental non-asymptotic time constants. The third is a model which claims to resolve the controversy between the diffusion and perfusion theories of gas transport in tissue. The result is that in the large, diffusion is more important than perfusion, except in muscle tissue where they interact. Three different methods of numerical inversion of the Laplace Transform are compared and one is shown to be the most useful for solving gas uptake problems. The main result of the thesis is a contribution to the establishment of a mathematical basis for gas transport in various situations in the biological sphere.