Lift and drag forces on a submarine pipeline in steady flow
Doctoral Thesis
1988
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University of Cape Town
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Abstract
This thesis describes an experimental investigation into the hydrodynamic forces induced on a cylinder placed transversely to a steady stream. Various cylinder locations near the bed of a water flume were considered. The work relates to pipeline design. The various flow phenomena around a cylinder are theoretically analysed and an explanation of the phenomenon of lift provided. A thorough literature review was undertaken regarding the classical theory, as well as experimental and theoretical studies carried out on the subject. This revealed that theoretical studies are virtually non-existent. Measurements have been done in intermediate water depths with both smooth and rough beds. Two different methods, comprising very simple yet novel techniques, were utilised in a water flume 18 m long x 600 mm wide x 450 mm deep. The methods involved a unique pressure determination method as well as the direct measurement of hydrodynamic forces, using a "weighing" method. Very ' accurate flow velocities were measured using a unique differential manometer. Experiments were performed in the Reynolds number range 6 000 to 26 000, using 30 and 50 mm diameter cylinders. comprehensive tests on cylinder roughening were carried out in a flow region which had not been well researched regarding this aspect. Cylinder locations were varied from a gap-to-cylinder diameter ratio of zero to 2,67. Results revealed that the force coefficients are not appreciably affected by bed roughness. Cylinder roughening produced somewhat contradicting results for the two different cylinders used. The influence on the lift coefficient was inconclusive, but the "rougher" 30 mm cylinder produced a slightly higher drag coefficient. Although the lift force was predominantly away from the bed, a downward lift force was measured on a few occasions with the cylinder situated further than one cylinder diameter away from the bed. A possible explanation is offered for this and other unexpected results. Flow visualisation tests were performed to confirm certain features of the flow around the cylinder. These as well as all the other results have been related to published work.
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Includes bibliography.
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Kok, N. 1988. Lift and drag forces on a submarine pipeline in steady flow. University of Cape Town.