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Title: The movement of solid particles by fluid streams
Author: Willetts, B. B.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1970
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The study begins with an examination of the literature, as a result of which it is concluded that the most significant impediment to further progress in the study of sediment transport is ignorance of grain dynamics. A simplified analysis is performed of the trajectory of a grain after dislodgement based on the assumption that the lift it experiences is due to circulation. The resulting grain path represents observed saltation paths with fidelity both in horizontal and inclined flow, but its utility is impaired by high sensitivity to the velocity gradient at the boundary, a quantity which can neither be calculated nor measured with great accuracy. To test the saltation model in an objective way, measurements of bed-load transport rate were made in a closed duct at a variety of angles of inclination and using four different materials. The results are compared with predictions made using the saltation analysis and a theoretical study of limiting equilibrium in the inclined duct. In view of the success of the comparison it is concluded that both the saltation analysis and the study of limiting equilibrium are probably correct in principle. The alternative, namely that both are wrong but that by coincidence they combine to give a reasonable, answer seems unlikely both inherently and by virtue of the observed fidelity of the saltation model. The validity of the study of equilibrium enables conclusions to be drawn about the manner of grain dislodgement. The bed-load transport rates measured in the duct are also-compared with partially theoretical treatments by earlier writers. These comparisons required that shear stress over the mobile bed be measured and this -was done with indifferent success. It is demonstrated that local shear, stress can be measured with a stagnation probe over the bed at the degree of grain mobility studied here. If the instrument-is placed at a nominated multiple of the grain diameter above a bed of uniform grains, then a "universal" calibration can be achieved in the plane Inadequate length of the experimental duct prevented a good calibration being achieved, in the study, yet even the curve obtained in these circumstances may improve on methods of estimating used hitherto. Those results for which direct comparison with earlier work was justified, agreed well with Yalin's prediction and, as might be expected from other work, showed greater bed mobility than would be predicted by Einstein. Little evidence was found that either.bed shear .stress or stream power is clearly to be preferred over the other .as independent parameter in sediment studies. Finally, it is suggested that further studies are needed of the lift force on a grain, of the interplay of this force with diffusion and of dislodgement. The strategies which might be adopted in such studies are outlined.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available