Experiments were carried out with smooth sharp-edged rectangular cylinders with different aspect ratios. The cylinders were horizontally submerged and tested in wavy flow and in combined steady and wavy flows to simulate the presence of currents along with waves. These experiments aimed at measuring inertia, drag and other force coefficients corresponding to low Keulegan-Carpenter numbers up to a value of 4. They also aimed at examining the effects of varying the aspect ratio and the presence of a current along∼ with waves in the hydrodynamic coefficients. The current effects m waves were simulated by towing the cylinders along the middle of the towing tank at Glasgow University at various constant speeds through oncoming regular waves. The various flow parameters such as Reynolds and Keulegan-Carpenter numbers, the reduced current velocity and the frequency parameter were systematically varied and the forces were measured. In wavy flow the drag coefficient had large values at small KC numbers and decreased sharply when KC number increased. The inertia coefficient was found to be strongly affected by the variation of the cylinders" aspect ratio. In combined waves and current flow, the results showed that both inertia and drag coefficients decreased when a current was present. In wavy flow the calculated forces using the Morison equation through the use of measured inertia and drag coefficients were found in good agreement with the corresponding measured forces. The calculated forces using the modified Morison equation taking into account the presence of a current with waves and using inertia and drag coefficients measured under no current conditions overestimated the measured waves-current induced forces.


Regular waves The design of offshore structures requires calculation methods to translate a definition of environmental conditions into the resultant steady and time dependent forces exerted on the structure.

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