Thesis (doctoral)--Reale Accademia di Scienze e Belle Lettere di Mantova, 1784. / Attributed to Antonio Ludeña. Signatures: a-c⁸ d³.

A scroll vortex intake is a hydraulic structure that transfers water stably from one elevation to a lower one by generating a swirling vortex flow down a vertical drop- shaft. Scroll vortex intakes are applied widely in water supply, stormwater drainage and sewerage systems. For a good engineering design, a sufficiently large and stable air core needs to be maintained within the dropshaft. Although a number of the- oretical and experimental investigations have been conducted, the understanding and predictions of the vortex flow is still far from complete due to a lack of de- tailed velocity field and air core measurements. This study aims to achieve a better understanding of the scroll vortex intake flow. The hydraulic theory of scroll vortex intake is revisited and detailed measurements of air core and velocity field of the vortex flow is conducted. A 1:15 physical model of a scroll vortex intake has been designed according to dynamic Froude similitude and constructed. Experiments have been conducted to measure the head-discharge relation. Piezometric head and air core size are measured at the throat of the vortex flow. Velocity fields are measured using Laser Doppler Anemometry (LDA). The measurements show that the vortex flow in the chamber resembles a free vortex and the circulation is approximately equal to that at the inlet to chamber. The chamber flow is not affected by the bottom boundary effect at bottom above a depth of the order of the dropshaft diameter. The throat section of the vor- tex flow is located slightly below the chamber bottom and within the bellmouth at the entrance to dropshaft. For the vortex flow in and downstream of the bell- mouth, the tangential velocity distribution can be described by a Rankine vortex (combination of forced and free vortex); the transition from forced to free vortex occurs at around the middle of the vortex flow layer. The pressure is positive for all locations and all discharges. Due to viscous effect, the maximum circulation is found to be lower than the inlet circulation. Consistent with the free vortex theory, the vertical velocity in the dropshaft is approximately constant. By accounting for the loss of circulation between chamber inlet and the dropshaft, a new 1D theory is proposed. Unlike previous models, the new theory gives good predictions of head-discharge relation and minimum air core size without the need of physically unrealistic assumptions. This study has revealed the structure of a scroll vortex intake flow for the first time. Characteristic flow features of the scroll vortex intake have been elucidated. The findings have helped to explain and resolve the long-standing discrepancies between the theoretical predictions of three representative 1D hydraulic theories. The vortex flow measurements also provide a basis for the development of a new theory and the validation of 3D numerical models. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

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published_or_final_version / Physics / Master / Master of Philosophy

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This thesis is concerned with the steering and manoeuvring of surface ships. Recent developments in hull design have seen the introduction of the pram stern. This hullform has proved less directionally stable than more conventional stern shapes. Recent theoretical developments include the effect of stern vortices in a slender-body treatment of the ships hull. The inclusion of these vortex effects explains the discrepancy between the distribution of force and moment coefficients along a hull obtained experimentally compared to those determined using slender body theory alone. As yet this approach requires the position and strength of the shed vortices to be determined by other means. The theory also offers a means of explaining the relative instability of the pram stern. An experiment has been designed to directly test some of the predictions of this theory. The experiment entailed oblique towing of a set of 7 hullforms with segmented stern sections. The first group of five models are based on the British Bombardier with a variety of conventional and pram stem configurations. The remaining models were based on a simple elliptic hullform. The experiments provide detailed data of the longitudinal distribution of force and moment sway derivatives of the stem regions of these models. The experimental evidence provided support for the theoretical predictions, although some results were inconclusive because of the effect of additional flow phenomena. The physical insight provided by the generalised slender body theory has generated the impetus to use a semi-empirical approach to predict the manoeuvring derivatives from basic hull geometry. The equations developed for the linear velocity derivatives use predictors based on the physical phenomena and are formulated to recognise the interdependency of these derivatives. The new equations are statistically more satisfactory than previous analyses of this type.