Unsteady flow around a circular cylinder has long been an area of interest to scientists and engineers, due to its significance in the engineering practice of structural design. In this paper, we investigate the flow around a cylinder subjected to waves experimentally and numerically. The vortex patterns around the cylinder measured by flume test and predicted by a RANS solver are compared. The in-line forces on the cylinder in unbounded oscillating flow are then studied numerically over a wide range of Reynolds and Keulegan-Carpenter numbers and the in-line force correlations between numerical simulation and Morison equation are presented.
Submarine cylindrical structures have been extensively used today and the safety of these structures has been increasingly concerned, along with the boom of offshore industry. In harsh ocean environment, the elements of these structures (e.g. risers, tendons and mooring lines) are subjected to various loads caused by ocean currents, waves, icebergs, earthquakes, etc. Among them, the forces of wave are the most highly interested one on two aspects. First, the asymmetric vortex shedding induces significant alternating forces on the structures. The vortex shedding and the corresponding induced forces on a circular cylinder have been investigated by a large number of researchers. Williamson (1988) observed different patterns of vortex shedding behind a cylinder at different Reynolds number. Williamson and Roshko (1998), Zdravkovich (1982) and Gu et al(1994) studied the vortex shedding of a forced vibrating cylinder. Anagnostoulos and Bearman(1992) and Khalak and Williamson(1996) considered the fluid-solid interaction and investigated the flow around a self-exciting cylinder by experiments. Tokumaru and Dimotakis (1991,1993) studied the vortex shedding behind a rotating cylinder and observed the suppression of vortex shedding due to rotation. All these related studies aimed to understand the mechanism of vortex shedding, so that the shedding can be controlled and the induced forces on the structure can be reduced.