Vortex-Induced Vibration of a Free-Hanging Riser Under Irregular Vessel Motion

Abstract

In this paper, we focus on vortex-induced vibration (VIV) of a free-hanging riser attached to a vessel under irregular wave conditions. The global in-plane responses of the hanging riser are firstly studied numerically in order to generate the equivalent current profile under vessel motion, and a simplified irregular vessel motion-induced VIV prediction methodology is then proposed based on the understanding from previous experimental observations and literature review. Further comparison on irregular vessel motion-induced VIV and ocean current-induced VIV at the same operation site with the same return period is performed to emphasize the importance of vessel motion-induced VIV. Numerical results highlight that vessel motion-induced VIV can cause similar stresses, fatigue damage and drag amplification similar to the steady ocean current cases, especially to the operation site like Norwegian Sea where strong wave field exists with mild current condition. It should be mentioned that although the simplified methodology proposed in this paper requires further experimental validation, it is believed that the presented numerical pre-study would help the industry and the researchers to have initial understanding on the possible occurrence of vessel motion-induced VIV. We further show the similarities and differences of vessel motion-induced VIV with respect to the ocean current-induced VIV and its implications on riser design and operation.

Vortex-induced vibration (VIV) effects of a drilling riser due to vessel motion

“…In case of irregular vessel motions, Wang et al [14] have proposed a method to generate the equivalent current profile in which the standard deviation of the velocity time series at each point along the length of the riser is multiplied by √2 to get the representative maximum. Hence the timevarying velocity can be simplified into an equivalent current profile according to equation (2).…”

Coupling Effects of a Top-Hinged Buoyancy Can on the Vortex-Induced Vibration of a Riser Model in Currents and Waves

“…In order to take the important platform motion into account while evaluating the VIV of a free-hanging riser, Qu et al [28] modified the wake oscillator by introducing relative oscillatory flow velocity. In addition, Wang et al [29], Duan et al [30], and many other researchers have also focused on the motion of floating bodies in VIV studies and suggested that this factor should be considered in VIV response and fatigue evaluation.…”