ABSTRACT

In this work, a series of tests was conducted in a recirculating water flume to investigate the dynamic behavior of a flexible catenary riser under the combination of internal liquid flow and external shear current. A non-intrusive high-speed imaging technique was employed to record the vibration displacement varying along the riser span. The experimental results illustrate that the response is enhanced with increasing the internal flow velocity except for the mode transition cases. When the internal fluid flows in the riser, the mode transition accompanying with the amplitude reduction occurs compared to the purely vortex-induced vibration response.

INTRODUCTION

Flow-induced vibration (FIV) of flexible structures is encountered in a wide range of engineering applications, especially in the offshore engineering. As oil and natural gas exploration extends to increasing deep waters, the flexibility of riser is enhanced. It is easy for flexible riser to experience an intricate vibration. The multi-mode vibration response of flexible risers has been the main object of a number of researches, as collected in Bourguet et al. (2011, 2013a, 2013b, 2020) and Fan et al. (2019). Mono- and multi-frequency vibrations may occur in both the in-line and cross-flow directions (Vandiver et al., 1996; Chaplin et al., 2005; Lucor et al., 2006; Bourguet et al., 2013b). As reported in Bourguet et al. (2013b), the profile of the normal component of oncoming flow is identified to control the mono- or multi-frequency nature of the response. In addition, the excitation region and the damping region correspond to the lock-in region and non-lock-in region, respectively. Owing to the multi-mode participation, the mixture of standing and traveling wave patterns often occurs in the flexible riser response (Bourguet et al., 2011; Bourguet et al., 2013a; Lucor et al., 2006; Newman and Karniadakis, 1997; Gao et al., 2019). Gao et al. (2019) reported that the aspect ratio can influence the wave patterns, which are dominated by standing waves for small aspect ratio cases. When the oncoming flow is a sheared one, the travelling wave usually prefers to propagate from the high inflow velocity to low inflow velocity (Bourguet et al. (2013a).

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