Under the effects of winds, waves and currents, the floating platform will harmonically oscillate in the water that generate the relative oscillatory flow. In this paper, numerical simulations on VIV of a flexible cylinder in the relative oscillatory flow are carried out by the in-house viv3D-FOAM-SJTU solver. Numerical results are in good agreement with experimental results. The specific "building-up – lock-in – dying-out" VIV developing process and the typical butterfly shape of vibration trajectory are observed. Three-dimensional vortex shedding and reattachment phenomena are observed during the reverse of the flexible cylinder when it reaches the leftmost or the rightmost position.
In deep sea oil and gas exploitation, Vortex-induced Vibration (VIV) phenomenon of marine risers is the main source of structural failure that contributes to severe damages to the ocean environment. During the past decades, VIV characteristics have been widely investigated by researchers and engineers all around the world, corresponding reviews can be referred to Williamson and Govardhan (2004), Sarpkaya (2004), Huang et al (2009), Ji et al (2015), Chen et al (2016), Wan and Duan (2017). Researches on VIV of a flexible riser exposed to the oscillatory flow are comparatively fewer than that in the steady flow conditions. Corresponding model experiments have been conducted to capture main VIV features of a rigid cylinder experiencing the relatively oscillatory flow under different Keulegan-Carpenter (KC) numbers, such as Williamson (1985), Sarpkaya (1986), Bearman (1989), Sumer and Fredsøe (1988) and Kozakiewicz et al (1997). Several representative vortex shedding regimes have been identified within a range of KC numbers. As for researches adopting the numerical method, Zhao et al (2012, 2013a, 2013b, 2014) carried out a series of simulations of a single circular cylinder and multiple circular cylinders in the oscillatory and combined flow respectively. Abundant valuable conclusions have been proposed in their researches. Similar researches can refer to Scandura et al (2009), Tong et al (2015), Pearcey et al (2017), Munir et al (2018) and Fonias and Grigoriadis (2018).