Turbulent flows past a cylinder is one of the most intensively investigated problem in fluid mechanics. The staggered shed vortices in the wake region exert oscillatory forces to the cylinder, and consequently excite the so called vortex-induced vibrations (VIV). Prediction and suppression of VIV are of special interest to the offshore industry because the cylinder represents a vast number of structural components in the offshore hydrocarbon exploitation. Our previous work, reported in the 20th Offshore Symposium of Texas SNAME by Wang et al, focused on the study of flow around rigid cylinders in uniform flow, with both Particle Image Velocimetry (PIV) experiment and Computational Fluid Dynamics (CFD) simulations. PIV measurements of the flow field at the downstream of the cylinder were first presented. The boundary conditions for CFD simulations were measured in the PIV experiment. Then the PIV flow was compared with both RANS (2D) and LES (3D) simulations performed with ANSYS Fluent. The velocity fields from PIV and CFD were compared in the time domain. In this work, the time-averaged velocity profiles and Reynolds stresses are analyzed. It is found that, in general, LES (3D) gives a better prediction of flow characteristics than RANS (2D). Subsequently, RANS simulations are performed in the case of alternating flow around a rigid cylinder and the results, for various combinations of Reynolds and Keulegan-Carpenter numbers, and the predicted drag force, as a function of time, is compared with that based on the classical Morison equation, as well as with experimental values reported in the API Manual.

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