### Abstract

[Truncated] Accurate predictions of the hydrodynamic forces and their variations in the frequency are essential for the design, construction and maintenance of the cylindrical structures such as pipelines and tension leg platforms in coastal and offshore engineering. The present study is concerned with the effect of the cylinder yaw angle (α= 0°, 15°, 30° and 45°) on the flow topology, momentum transport and the hydrodynamic forces around a square cylinder in steady current and oscillatory flow. Based on these studies, the independent principle (IP) can be evaluated when applied to a yawed square cylinder under these two flow conditions.

For a yawed square cylinder in steady flow, the vortical structures at different yaw angles are investigated using hot-wire technique, numerical simulation and particle image velocimetry (PIV). The phase-averaging method extracts the coherent and incoherent components of velocity and vorticity fluctuations based on the hot-wire measurement at the intermediate wake of the cylinder. The maximum magnitudes of the coherent spanwise vorticity decrease as 훼 increases. The contours of the spanwise velocity, however, experience an increase in the maximum magnitudes with the increase of 훼. It is also found that the Strouhal number and the mean drag coefficient, normalized by the velocity component normal to the cylinder axis, follow the IP satisfactorily up to α= 40°. Besides, the comparisons with previous studies indicate that the cylinder yaw angle has a stronger effect on the square cylinder wake than that on the circular cylinder one.

For a yawed square cylinder in steady flow, the vortical structures at different yaw angles are investigated using hot-wire technique, numerical simulation and particle image velocimetry (PIV). The phase-averaging method extracts the coherent and incoherent components of velocity and vorticity fluctuations based on the hot-wire measurement at the intermediate wake of the cylinder. The maximum magnitudes of the coherent spanwise vorticity decrease as 훼 increases. The contours of the spanwise velocity, however, experience an increase in the maximum magnitudes with the increase of 훼. It is also found that the Strouhal number and the mean drag coefficient, normalized by the velocity component normal to the cylinder axis, follow the IP satisfactorily up to α= 40°. Besides, the comparisons with previous studies indicate that the cylinder yaw angle has a stronger effect on the square cylinder wake than that on the circular cylinder one.

Original language | English |
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Qualification | Doctor of Philosophy |

Publication status | Unpublished - Sep 2015 |